all about space book of the solar system - 2014

8/17/2019 All About Space Book of the Solar System - 2014

1/180


2/180


3/180

As Man continues to search for new discoveries in space, and answers to some of life’s

biggest questions – such as are we alone in the universe? – our desire to understand

more about our place in the universe has led to us gaining a better understanding of

the Solar System. In this book we take a closer look at the star that lies at the centre of

our Solar System. Discover the impact the Sun has on our lives and everything

around us, and nd out how this ball of hot plasma formed. Read about the eight

planets that make up our Solar System, whether you want to learn why Saturn has

rings, how life formed on Earth, if we could live on Mars, or why Neptune looks so

blue. On top of that, you can nd out about four of the most interesting moons of the

Solar System; Ganymede, Europa, Titan and our very own Moon. See what rolesthese satellites play, and why they are so important. Packed with essential guides and

incredible illustrations, this book will help bring the Solar System to life!

Welcome to the

SolarSystem

BOOK OF THE


4/180


5/180

Imagine Publishing LtdRichmond House33 Richmond Hill

BournemouthDorset BH2 6EZ

+44 (0) 1202 586200Website: www.imagine-publishing.co.uk

Twitter: @Books_ImagineFacebook: www.facebook.com/ImagineBookazines

Head of PublishingAaron Asadi

Head of DesignRoss Andrews

EditorJon White

Senior Art EditorGreg Whitaker

DesignerLauren Debono-Elliot

PhotographerJames Sheppard

Printed byWilliam Gibbons, 26 Planetary Road, Willenhall, West Midlands, WV13 3XT

Distributed in the UK & Eire by Imagine Publishing Ltd, www.imagineshop.co.uk. Tel 01202 586200

Distributed in Australia by Gordon & Gotch, Equinox Centre, 18 Rodborough Road, Frenchs Forest,

NSW 2086. Tel + 61 2 9972 8800

Distributed in the Rest of the World by Marketforce, Blue Fin Building, 110 Southwark Street, London, SE1 0SU

DisclaimerThe publisher cannot accept responsibility for any unsolicited material lost or damaged in the

post. All text and layout is the copyright of Imagine Publishing Ltd. Nothing in this bookazine maybe reproduced in whole or part without the written permission of the publisher. All copyrights are

recognised and used specifically for the purpose of criticism and review. Although the bookazine hasendeavoured to ensure all information is correct at time of print, prices and availability may change.

This bookazine is fully independent and not affiliated in any way with the companies mentioned herein.

All About Space Book of the Solar System © 2014 Imagine Publishing Ltd

ISBN 978-1909758483

bookazine series

Part of the

SolarSystem

BOOK OF THE


6/1806

ContentThe Sun The planets The moons10 The SunExplore the star keeps us all alive22 Solar ares

A look at how these can pose a real risk

28 The hole in the SunFind out more about NASA's discovery

30 Solar maximumRead about the activity of the Sun

134 The MoonEarth's only satellite explained

146 GanymedeDiscover the most planet-like moon

156 EuropaCould this moon be capable ofsupporting life?

166 TitanExplore one of Saturn's 63 moons

42 MercuryLearn about the planet closest to the Sun

52 VenusExplore Earth's twin planet

64 EarthFind out more about our home planet

76 MarsCould there be life on Mars?

88 JupiterUncover amazing facts about this gas giant

100 SaturnRead about how Saturn's rings formedand much more

112 Uranus Explore the solar system's

forgotten planet

122 Neptune Discover all you need to know about thefrozen planet


7/180


8/1808

10 All about the Sun Explore the star keeps us all alive

22 Deadly solar ares A look at the Sun's deadly activity

28 The hole in the Sun Find out more about NASA's discovery

30 Solar maximum Read about the activity of the Sun

Discover the star at the centre of our Solar System

The Su


9/180

“A solar flare is a suddenincrease in the brightness on

the surface of the Sun


10/180

10

The Sun

1010


11/180

The Sun

The vast nuclear furnace that we know as theSun is responsible for dictating the seasons

climate and characteristics of every planet inthe Solar System. Here, we take an in-depth

look at this source of power that has astoundehumanity since the dawn of existenc

THE

SUN

All About…


12/180


13/180

The Sun

Layers of the Sun

Scutum-Centarus arm

The Sun

Outer arm

rion spur

Perseus arm

Our Solar System is located in the outerreaches of the Milky Way galaxy, which hasroughly 200 billion stars

SpiculesThese supersonic jets ofhot plasma form in theSun’s interior and rise to aheight of around 5,000km(3,000 miles) above theSun’s photosphere

Coronal mass

ejectionsA coronal mass ejection(CME) is a burst of plasmaand magnetic fields,known as stellar wind,being thrown into spacefrom the Sun’s corona

FaculaeProduced byconcentrations ofmagnetic field lines,these bright spotsappear on the Sun’schromosphere inregions where asunspot will form

GranulationThe Sunoften appearsgranulated inimages becauseof convectioncurrents in itsphotosphere andchromosphere

ProminencesThese large loopsof energy extendoutwards from theSun’s corona. Theycan range over700,000km(430,000 miles),approximately theradius of the Sun

SunspotThese dark spots on the surfaceof the Sun are caused by intensemagnetic fields and are usuallyaccompanied by a solar flare or CME

PhotosphereThe visible surface of theSun, the photosphere,has a temperature of5,530°C (9,980°F)and is made mostly ofconvection cells,giving it a granulatedappearance

ChromosphereThis thin layer about 2,000km(1,240 miles) thick sits just above thephotosphere and is the area wheresolar flares and sunspots are visible

Radiative zoneThis area is full of electromagnetic

radiation from the core that bouncesaround as photon waves. It makes up

about 45 per cent of the Sun

Inner coreMost of the Sun’s fusion poweris generated in the core, which

extends outwards from thecentre to about a quarter of the

Sun’s radius

CoronaThe outer

‘atmosphere’of the Sun.

It is madeof plasma,

extends

millions ofkilometres

outwards andhas a higher

temperaturethan the inner

photosphere


14/180

14

The Sun

14

Like the Earth, the Sun has an atmosphere, but the two are very different. TheSun’s can be incredibly volatile with powerful magnetic activity that causesphenomena referred to as solar storms here on Earth

Solar storms are violent outbursts

of activity on the Sun that interfere

with the Earth’s magnetic field and

inundate our planet with particles.

They are the result of outpourings

of energy from the Sun, either in theform of a Coronal Mass Ejection (CME)

or a solar flare. The former is a release

of a large amount of material, mostly

plasma, from the Sun while the latter

is a sudden release of electromagnetic

radiation commonly associated with a

sunspot. While no direct connection

has been found between CMEs and

solar flares, both are responsible for

Solar stormscausing solar storms on Earth. The

reason why these two events occur

is due to the Sun’s atmosphere and

its turbulent interior, with all of its

components playing a part in bathing

our planet in bursts of energy.The lowest part of the atmosphere,

the part directly above the Sun’s

radiative zone, is the photosphere.

This is the visible part of the Sun that

we can see, it is 300400 kilometres

(180240 miles) thick and has a

temperature of about 5,530 degrees

Celsius (9,980 degrees Fahrenheit).

This produces a white glow although

from Earth this usually appears yellow

or orange due to our own atmosphere.

As you travel through the

photosphere away from the Sun’s

core the temperature begins to drop

and the gases become cooler, in turnemitting less light. This makes the

photosphere appear darker at its outer

edges and gives the Sun an apparently

clearly defined outer boundary,

although this is certainly not the case

as the atmosphere extends outwards

much further.

Once you pass through the

photosphere you enter the

chromosphere, which is about 2,000

kilometres (1,240 miles) thick. The

temperature rises to about 9,730

degrees Celsius (17,540 degrees

Fahrenheit), surpassing that of the

photosphere. The reason for this isthat the convection currents in the

underlying photosphere heat the

chromosphere above, producing shoc

waves that heat the surrounding

gas and send it flying out of the

chromosphere as tiny spikes of

supersonic plasma known as spicule

The final layer of the Sun’s

atmosphere is the corona. This huge

Solar wind and the Earth

Solar windAside from solar flares the Sunis continually emitting radiationand particles in all directions inthe form of solar wind

Solar flareThe formation of a pair of sunspotson the Sun’s surface creates amagnetic field line loop, which canin turn snap and send a violenteruption of material spewing out

MagnetosphereAs these particles travel towardsEarth they encounter themagnetosphere of our planet andtravel along the magnetic field lines

AuroraParticles from the Sun can exciteand heat particles at the poles ofEarth, forming fantastic displaysof light known as the auroraborealis and aurora australis in thnorth and south respectively


15/180


16/180

16

The Sun

16

Our Sun may be a great distance away

but its f luctuations and perturbations

are still felt here on Earth.

Every 11 years the Sun moves from

a period of low activity, known as a

solar minimum, to a period of high

activity, known as a solar maximum,

and back again. When it is at itsmost active the Sun is even more

violent than usual, with a greater

number of sunspots appearing on

its surface and therefore more solar

flares emitted into space. During its

minimum point it is still a raging

inferno firing material into space but,

by comparison, it is much quieter

and sunspots, and therefore solar

storms, are rare.

Cycles are observed by monitoring

the frequency and position of

sunspots on the Sun. When the Sun

reaches the end of its cycle, new

sunspots will appear near the equator.The beginning of the next cycle

will see su nspots appear at higher

latitudes on the surface of the Sun.

Solar cycles have been observed for

centuries, but a standardised method

of counting them was not devised

until 1848 when Johann Rudolf Wolf

started counting sunspots on the solar

disk and calculated the Wolf number,

which is still u sed today to keep track

of the solar cycle. Cycles vary in their

intensity. From 1645 to 1715 there

were few sunspots present on the

Sun, a period known as the Maunder

Minimum. The number of sunspots

has been relatively more uniformthis century, with cycles having an

average period of 10.5 years. The Sun

also has a 22-year magnetic cycle

where, every 22 years, its magnetic

field flips from pole to pole. This

doesn’t have a noticeable effect on

the Solar System, but indicates when

the solar maximum of the current

cycle has been reached. However,

the reason for these cycles remains

a mystery. No one yet has any clear

understanding as to why the Sun has

periods of varying activity.

Our Sun is ever-changing,affecting all life on Earth andour natural environmentThe solar cycle

10 years of the SunThese X-ray images were taken by Japan’s

Yohkoh Solar Observatory and show the changesin the Sun’s corona over a ten-year cycle between

30 August 1991 and 6 September 2001

19911993At the start of this solarcycle there were about 200sunspots on the surface ofthe Sun per month

19941996As the Sun’s activity began towane, the number of sunspots pyear dropped from about 100 pmonth in 1994 to 75 in 1996


17/180

The Sun

How we understand solar cycles“Sun-Earth interaction is complex, and we haven’t yet

discovered all the consequences of solar cycle variation

on Earth’s environment. We saw a large amount of

geomagnetic activity driven by recurring fast solar wind

streams during the recent solar minimum. A surprising

departure from the consistently low activity we’d come

to expect from previous minima, especially considering

the record low level of sunspots. These new observations

deepen our understanding of how solar quiet intervals

affect the Earth and how and why this might change

from cycle to cycle.”

The Scientist’s view

Solar cycles have been observed forcenturies, but a method of counting

them was not devised until 1848”

Sarah Gibson, UCAR, @AtmosNews

The Sun by

numbersFantastic figures and surprisingstatistics about our nearest star

The Sun’s percentage of massof the entire Solar System

99.86%

5%Lessthanof stars inthe Milky Way are brighter orlarger than the Sun

1

millionEarthsWould fit insidethe Sun

498second

How long it takes light to travel from the S

164 watts Is the amouof energy every squaremetre of the Earth’s surfareceives. That’s the equivaof a 150-watt table lamp every square metre of the Earth’s surface

100 BILLIONTons of dynamite wouldhave to be detonated everysecond to match the energproduced by the Sun

19992001The Sun’s activity increased againto a solar maximum, with up to 175sunspots appearing per month

19971998The Sun reachedits period of solar

minimum betweenthese years, fallingto almost zerosunspots per month


18/180

18

The Sun

The Solar and Heliospheric Observatory was launched inDecember 1995 and is helping us explore the Sun

The Solar and Heliospheric

Observatory, also known as SOHO, was

launched on 2 December 1995. It was

built in Europe by pri me contractor

Matra Marconi Space, which is now

EADS Astrium. The spacecraft is

operated jointly by the ESA and NASA.

It studies the Sun in depth, all the way

from its deep core to its outer coronaand its solar wind.

SOHO is made of two modules,

the Service Module and the Payload

Module. The former provides SOHO

with power, while the latter houses all

of the instruments on the spacecraft.

Overall, there are 12 instruments on

board SOHO, nine of which a re run

by Europe a s well as t hree from t he

United States.

SOHO is located near to Lagrangian

point 1, which is a point between the

Earth and the Sun about 1.5 million

kilometres (930,000 miles) from

our planet. It is the point where thegravitational attraction of the Sun and

the Earth cancel out, so a telescope

such as SOHO can remain in a stable

orbit to observe the Sun. SOHO is

one of the only telescopes currently

capable of detecting incoming solar

flares that could be potentially

hazardous to satellites and other

electronics on Earth.

Of the 12 instruments on board

SOHO one of the most interesting is

the Large Angle and Spectrometric

Coronagraph (LASCO), which

studies the Sun’s corona bycreating an artificial solar eclipse.

The LASCO instrument has been

largely responsible for inadvertently

discovering many comets near the

Sun, with over 1,800 found to date.

SOHO has three primary objectives

that it has been carrying out since

its launch. One of these was to

investigate the outer regions of the

Sun, specifically the corona.

At the moment it is st ill u nknown

why the corona is hotter than the

photosphere and chromosphere of

the Sun, so it is hoped that SOHO

might help to provide the answer inthe future. SOHO has also been used

to observe the solar wind, and also

to study the interior structure of the

Sun through a process known

as helioseismology.

The SOHO mission

Take atour of

SOHOSOHO is made up

of two modules.The Service

Module formsthe lower portion,while the Payload

Module sits above

On the scale of solar flares, X-class storms are most powerful. SOHO took this image onNovember 2003 showing the most powerful ever recorded, which reached X28

Payload ModuleThis sits on top of the

Service Module and housesall 12 of the instruments on

board the spacecraft

Service ModuleThe Service Module

provides power,telecommunications,

thermal control anddirection to the spacecraft

MalfunctionIn 1998 SOHO suffered

a major malfunction thatalmost rendered it unusable.

However, some smartthinking enabled scientists

to regain control of thetelescope, although it nowoperates without the help

of its gyroscopes, theonly three-axis stabilised

spacecraft to do so

SOHOprojectscientistBernhard

Fleck tells us whystudying the Sun isimportant to Earth

Interview

1. Understand life“The Sun provides the energy for alllife on Earth. It seems quite naturalthat we are curious to know moreabout the star from which we live.”

2. Understand climate“Solar radiation is the dominantenergy input into the terrestrialecosystem. The Sun provides a

natural influence on the Earth’satmosphere and climate. Tounderstand mankind’s roles inclimate change, the Sun’s impactmust be understood.”

3. Predict space weather“Our Sun is very dynamic andproduces the largest eruptionsin the Solar System. These solarstorms can reach our planet andadversely affect technologies suchas satellites and power grids. Spaceweather becomes increasinglyimportant as our society dependsmore on modern technologies.”

4. Learn about stars“If we want to understand theuniverse, we have to understandthe evolution of galaxies. Tounderstand galaxies, we need tounderstand the evolution of starsthat make up the galaxies. If wewant to understand stars, we betterunderstand the Sun, the only starwe can resolve in great detail.”

5. Stellar physics lab“The Sun lets us study basic physicalplasma processes under conditionsthat can’t be reproduced on Earth.”


19/180

The Sun

The SOHOspacecraft hassurvived 17years in space,15 more thanits initialmission length

“SOHO is located near to Lagrangian 1 which is a point between the Earth

and the Sun about 1.5 million km(930,000 miles) from our planet

LASCOSOHO’s Large Angle andSpectrometric Coronagraph(LASCO) produces detailedimagery of the solar corona bycreating an artificial eclipse

Solar panelsSOHO’s only source of energyis from the Sun, but as it is inorbit around it it has a large

supply of energy

AntennasSOHO transfers data back toEarth at a rate of between40Kbits/s and 200Kbits/s usinits high and low gain antennas

Solar and

HeliosphericObservatory (SOHO)

MissionProfile

Mission dates: 02/12/9512/12/14

Details: SOHO is a joint project

between the ESA and NASA. It

was designed to study t he origin

of the solar wind, the outer

atmosphere of the Sun and its

internal structure. SOHO has

found over 1,800 comets to date

and discovered that quakes on t

Sun’s surface are caused by solar

flares. It has also made the most

detailed map of features on the

solar surface.


20/180

20

The Sun

Humanity has been fascinated by theSun for thousands of years and evenprimitive records still prove useful.Discover more about the past, presentand future of studying the SunObservations of the Sun have

been used for both scientific andreligious observations for millennia.

Civilisations have used the Sun

to keep an accurate count of days,

months and years since at least

300BC, while scientists such as Galileo

studied the Sun through telescopes to

discern some of its characteristics.

At the Chankillo archaeological site

in Peru can be found the oldest solar

observatory in the Americas, a group

of 2,300-year-old structures used to

track the motion of the Sun known

as the Thirteen Towers. These towers

provide a rudimentary solar calendar

through which the Sun can be traced.The towers, each between 75 and

125 square metres (807 and 1,345

square feet) in size, run from north

to west along a ridge along a low hill.

From an observation point to the west

of the ridge the Sun can be seen to

rise and set at different points along

the ridge, which allowed ancient

civilisations to track the number of

days it takes the Sun to move from

tower to tower.

Much later, in 1612, the renowned

Italian astronomer Galileo Galilei

(15641642) used his telescope to

make one of the first observations of

sunspots on the surface of the Sun. In1749 daily observations began at the

Zurich Observatory and, since 1849,

continuous observations have been

made to count the number of sunspots

“Civilisations have used theSun to keep an accurate

count of days, months andyears since at least 300BC

present on the Sun’s surface at any

one time.Fast forward to today and, aside

from SOHO, one of the primary

telescopes used to observe the sun

is the Japanese Hinode spacecraft.

Hinode is a telescope in sun-

synchronous Earth orbit, which allows

for nearly continuous observation

of the Sun. It was launched on 22

September 2006 and was initially

planned as a three-mission study of

the magnetic fields of the Sun, but its

mission has since been extended as it

continues to operate nominally.

Another important Sun-observ ing

telescope is the Solar DynamicsObservatory (SDO), launched by NASA

in 2010. The goal of the SDO is to

study the influence of the Sun near

Earth, predominantly how the Sun’s

magnetic field is responsible for the

solar wind once it is released into the

heliosphere. It should help scientists

further understand the Sun’s influence

on the Solar System.

In the future, NASA’s Solar Probe

Plus will be the closest spacecraft to

Observing

the Sunthe Sun, approaching to within just 8.5

solar radii (5.9 million km, 3.67 millionmiles, 0.04 AU) after its launch in

2018. It will probe the outer corona of

the Sun in unprecedented detail, while

also becoming the fastest spacecraft of

all time in the process at up to 200km

per second (120 miles per second).

Apart f rom million dollar telescopes,

many amateur astronomers around

the globe today observe the Sun either

for entertainment or educational

benefit. Using specially designed

glasses people can look at the Sun

from Earth, although caution must be

taken to limit time spent looking at

the Sun and it should never be lookedat with the naked eye. Other methods

of solar observation include using a

telescope to produce a trace of the

Sun, a method similar to that used b Aristotle and his ca mera obscura in

the 4th Century BC. Again, precautio

must be taken here, as under no

circumstances should the Sun be

directly observed through a telescop

Whatever the method, and whatev

the mission, observations of the Sun

have been a long tradition and will

continue to be so for the foreseeable

future. Astronomical events such as

planetary transits and solar eclipses

provide amateur astronomers with

opportunities to see extraordinary

solar phenomena, while agencies

throughout the world will continue tstudy the Sun and learn more about

how the fantastic star works.

The history ofobserving the Sun

400BCThe world’s oldest solarobservatory, the Thirteen Towersof Chankillo, is built in Peru totrack the motion of the Sun.

350BCAristotle uses a cameraobscura to project animage of the Sun andobserve a partial eclipse.

1612Galileo Galilei uses histelescope to make one of thefirst observations of sunspotson the surface of the Sun.

Solar eclipses are apopular time to view theSun but using the correct

viewing equipment is veryimportant for safety


21/180

The Sun

1749Daily observations of theSun begin at the ZurichObservatory in Switzerland.

1849New observatoriesaround the world allowcontinuous observationsof sunspots to be made.

2006The Japanese telescopeHinode is launched to studythe magnetic fields andatmosphere of the Sun.

2010NASA launches the SolarDynamics Observatory, itsprimary goal being to study theinfluence of the Sun near Earth.

2018NASA’s new Sun-observitelescope Solar Probe Pllaunch and become the cspacecraft to the Sun.

Different ways toobserve the SunOn Earth we perceive the Sun to

be a yellow ball of gas in the sky but, like anything as hot as the

Sun, it is actually closer to being

white hot when viewed from

space. There are several telescopes

currently observing the Sun but

the large majority of our images com

from the STEREO telescope andthe SOHO observatory, both in orbit

around the Sun. By viewing the Sun

different wavelengths we can study i

different characteristics and see som

of its main features in a different ligh

UltravioletImages of the Sun in ultraviolet light arebetween wavelengths of about 19.5 and 30.4nanometres. Such an image of the Sun is at thelower end of this scale, and allows us to seewhere the lower part of the corona and upperpart of the chromosphere combine. The lightin this image comes from active regions in theSun’s chromosphere.

X-rayLight with a wavelength shorter than tennanometres (ten billionths of a metre) is knownas X-ray light. X-rays are emitted from the Sun’scorona, the hottest visible layer of the Sun’satmosphere. The visible areas of brightness areplaces where more X-rays are being emitted,around areas of increased activity on theSun’s surface.

VisibleVisible light images commonly refer to thoseviewing the Sun in white light, which showsthe true colour of the white-hot Sun. In visiblelight images we can see the Sun’s photosphere,which is about 6,000 degrees Celsius (10,832degree Fahrenheit) and therefore appearswhite-hot. Here, we can see dark spots on thesurface of the Sun, known as sunspots.

InfraredInfrared light is responsible for more thanhalf of the Sun’s power output, typicallyaround wavelengths of 1,080 nanometres.Infrared images show features of the Sun’schromosphere and corona. The dark featureson the image are areas where the gas is moredense, absorbing more infrared light than inother areas.

A telescope witha digital screencan be used tosafely observethe Sun


22/180

22

The Sun

What would become of the Earth if a large solar storm was directed our way,and would we be able to survive such an event? We take a look at how theSun’s activity has threatened life on Earth before, and how it might again

SOLAR FLARESDEADL


23/180

Deadly solar flare

The Earth is under constant threat from a whole

host of things in space, from asteroids to comets.

However, the one thing that is essential to life on

our planet, the Sun, may also be the most dangerous

threat of all to life as we know it. “[A large solar

flare] would certainly have a widespread ubiquitous

footprint all the way around the world,” said JoeKunches from the National Oceanic and Atmospheric

Administration’s (NOAA) Space Weather P rediction

Center (SWPC), which provides solar weather

forecasts to satellite operators and agencies across the

globe. “The question is, how deep would the effects

be, and how long would it take to recover from that?”

The Sun is a volatile and dangerous ball of gas

that, while it is the heart of our Solar System, also

has the potential to wreak havoc on not only our

world but the other planets and moons as well. It is a

constantly churning furnace of energy that releases

radiation into its surroundings. As our closest star it

is the perfect laboratory to observe how such stars

behave, and indeed we have been studying the Sun

for centuries to try to further our understanding of it.

While the Sun is constantly emitting energy andradiation, it goes through a period of cycles that tend

to govern how active it is at any given time. The

solar magnetic activity cycle has a period of 11 years,

and at its peak it significantly increases detectable

changes and emissions from the Sun including

sunspots and solar flares. It is at these times, during

a solar maximum, that the Earth’s infrastructure

is under greatest threat. In the last few decades

organisations like the SWPC have used a multitude of

observatories both in space and on Earth to monitor

these cycles and to predict when a large solar event

could endanger our planet.

“There have been plenty of cases of serious

damage to satellites,” said Kunches. “It happens

mostly when the Sun is active and very eruptive atthe peak of the solar cycle, and right now we’re at the

peak of the current solar cycle, although this one has

been pretty uneventful.” However, based on previous

experiences, Kunches knows that the SWPC cannot

take anything for granted. “During the last solar

maximum era, around Halloween in 2003, there was

a two-week episode of very turbulent space weather

conditions,” he said. “There were documented cases

of satellite failures, and some total failures.”

A solar flare is a sudden increase i n brightness

on the surface of the Sun. It occurs when built-up

magnetic energy in the solar atmosphere is released,

resulting in a huge emission of energy equivalent to

millions of 100-megaton nuclear bombs exploding

simultaneously. This energy is usually the result ofclosely occurring loops of magnetic force extending

out from the Sun’s surface and, if they ‘snap’, a burst

of solar wind combined with magnetic fields known

as coronal mass ejections (CME) will be emitted. A

solar flare itself is an ejection of clouds of electrons,

ions and atoms, with a CME usually following the

flare. Solar flares and CMEs both usually result

from the collapse of magnetic field loops, but the

relationship between the two is not fully understoo

The breaking of a magnetic field loop is usually

indicated by the appearance of sunspots, visibly

dark areas on the Sun occurring in pairs. The reason

for 11-year solar cycles, when these emission events

increase, is still under debate.

The study and detection of these solar phenomenhas been carried out for decades by various

observatories and telescopes. These include the

space-based Solar Dynamics Observatory (SDO) and

the Solar and Heliospheric Observatory (SOHO), the

InsideSDOThere are a multitude of

telescopes and observatori

constantly observing the

Sun, but NASA’s Solar

Dynamics Observatory

(SDO) is currently able toget some of the highest-

resolution images of our

Solar System’s central star

from its orbit around the

Earth. Launched on 11

February 2010, the SDO’s

main goal is to understand

the influence of the Sun

on Earth and surrounding

space by measuring in

several wavelengths

simultaneously.

MassAt launch the SDOweighed 3,100kg(6,800lb), withthe instrumentsweighing 300kg(660lb), thespacecraft itself1,400kg (3,090lb)and the fuel1,400kg (3,090lb)

Extreme UltravioletVariability Experiment (EVE)EVE measures the extreme ultraviolet emissionof the Sun to understand the relationshipbetween its ultraviolet and magnetic variations

Solar arraysThe solar panelsspan 6.25m(20.5ft) andsupply 1,540watts of powerto the SDO at anefficiency of 16%

Helioseismicand MagneticImager (HMI)

The HMI producesdata that helps to

determine howactivity inside

the Sun producesvisible effects on

its surface

Atmospheric ImagingAssembly (AIA)The AIA allows for continualobservations of the entireSun in seven extremeultraviolet channels from atemperature of 20,000 to20 million Kelvin

“We rely on infrastructure that is knownto have sensitivities to space weather”

Joe Kunches, far right, is part of the SWPCteam that provides space weather forecasts

for satellite operators around the world


24/180

24

The Sun

It takes about 60 hours for theEarth to feel the effects of asolar flare or CME

former run by NASA and the latter run jointly by ES

and NASA. “In the satellite world there are at least te

spacecraft that provide real-time information to the

SWPC,” said Kunches. “Then in addition to that ther

are ground-based observatories, and also ground-

based sensors like mag netometers. If you put a roun

number on it there would be about 50 to 100 senso

contributing to the real-time information stream tha

we tap into here.”

The work of the SWPC, and other similar

organisations, is hugely important in protecting

ourselves from the Sun. Although predicting the

occurrence of world-changing solar events is

important, it is largely everyday satellite operators

that rely most on the solar weather predictionorganisations in ensuring that their spacecraft rema

operational and continue to provide the service the

are intended to. They use regular bulletins from

places like the SWPC to know when to prepare for

a solar event. However, contrary to popular belief,

satellites are not shut down if a solar storm is

incoming because the danger of a satellite failing if

is turned off and on is fairly high. Some instrument

can be turned off and ground teams can prepare for

the worst but, as Kunches put it, “you can’t run and

you can’t hide.”

The SWPC is able to produce accurate forecasts fo

up to the next 27 days detailing what sort of activity

the Sun is expected to go through. If a solar flare or

CME is seen by one of the many active telescopes,

it takes about 60 hours for the Earth to feel theeffects of such an event. However, as Kunches

explained, just detecting the event is not enough.

The SWPC must track the emission as it makes its

way towards Earth to discern when it will arrive an

how powerful it will be, with the latter known as th

magnitude. “Ten years ago we could get the timing

down to plus or minus 12 hours,” said Kunches. “No

we’ve cut that in half, but it’s not easy being accurat

It’s 150 million kilometres (93 million miles) from th

Sun to the Earth and a lot can happen in-between.”

While working out the timing of an incoming

solar flare is becoming more accurate, it is the size

of such an event that proves the most troublesome.

Inside asolar flare

ProminenceA loop of plasmaextends fromthe Sun’s surfaceinto its hot outeratmosphereduring a solarflare event

Magnetic fieldThe prominence has twocontact points with the Sunas it flows along the magneticfields created inside the Sun

CharacteristicsA coronal mass ejection(CME) usually followsa flare, containing abillion tons of matter andtravelling at millions of

kilometres per hour

RadiationThe flare releasesradiation acrossthe entireelectromagneticspectrum, from radiowaves to X-rays

TemperatureInside a solar flare thetemperature can reachanywhere from 10 milliondegrees Kelvin to 100million degrees Kelvin

The SWPC is one of nineNational Centers forEnvironmental Prediction, but the only one dedicated tospace weather forecasting


25/180

Whathappenswhen

a solarflare hitsEarth?

ObserversA variety ofobservational spacecrincluding the SDO,STEREO and SOHO areused to predict whenthe Sun will erupt andhow powerful theeruption will be

SpacecraftelectronicsHard X-rays from anincoming solar flare candamage the internalelectronics of spacecraftand prevent instrumentsfrom working

Telephone mastEven cell phones are not adverseto the effects of solar flares, asthe increased activity can preventdevices communicating withtelephone masts

GPS failureIncreased solar activity can prevent GPSnavigation satellites operating functionallyand, as most are in a similar orbit, one is notable to provide backup for another

PipelinesTelluric currents, thosefound in long pipelines,can be affected by solarflares when systemsdesigned to protect pipelines

from corrosion areoverloaded

AircraftIn the event of increased solaractivity aircraft must avoidflying near the poles and athigh latitudes to ensure thatcommunications aren’t affecte

AtmosphereSoft X-rays from X-class flarescan increase the ionisation ofthe atmosphere so that, whileit might produce fantasticauroras, it also interferes withradio communication

Orbital decayIncreased ionisation ofthe atmosphere causedby solar storms canincrease the drag onsatellites, decaying theirorbit, as was the casewith NASA’s Skylabspace station in 1979

Power gridIncreased solar activity cancause geomagnetic storms,which have been known toknock out power grids toentire cities in the past

International Space StationRadiation risks for astronauts onthe ISS are minimal, but for futureastronauts travelling to deep spacelocations like Mars they could bemore severe


26/180

26

The SunThe Sun

How asolar flareinteracts

with Earth

EmissionA solar flare sendsa stream of chargedparticles and radiationtowards Earth

“The hardest thing for us to predict is the magnitude,”

said Kunches. “There’s a key element that plays into

the magnitude, how disturbed the Earth’s magnetic

field is going to get, and that’s the strength of the

embedded magnetic field that’s contained within the

CME. Think of a hurricane; if the weather forecasters

knew the direction of it, and they had some sense of

how fast it was moving, but they had no idea of the

strength of the eye of the storm, it’d be very difficult

to know how much of an impact it was going to have

as it made landfall, and that’s kind of analogous to

what we have in space weather forecasting.”

Solar flares are classified in magnitude according

to the number of watts per square metre they carry,

and their frequency. A-class flares are the most

frequent and the least powerful, increasing in powerthrough B, C, M and finally X. The latter are the ones

that are the most dangerous to Earth. The magnitude

of a solar storm will determine how much of an

impact it will have on Earth.

The largest recorded geomagnetic solar storm

caused by a solar flare was the Carrington Event

in 1859. Observed by British astronomer Richard

Carrington, the storm was noticeable around

the world. Auroras reached as far south as the

Caribbean, while it was reported that residents of the

northeastern US could read a book by the light of the

aurora. Of most concern, however, was that telegraph

offices all over Europe and North America failed,

with some throwing sparks or catching fire. This led

to much speculation about the effects a similar stor

would have in the modern world, where electronics

are a much more integral part of our lives.

In March 1989 that question was answered when

large CME coupled with a solar flare caused a sever

geomagnetic storm on Earth. Although it temporari

knocked out some satellites and spacecraft, the wor

effects of the storm were felt in Québec, Canada.

The variations in the Earth’s magnetic field, coupled

with Québec’s location on a large rock shield that

prevented the flow of current through the Earth,

tripped the circuit breakers in the power grid of the

Hydro-Québec power station and knocked the statio

offline, sending 6 million people into a blackout

lasting nine hours.The geomagnetic storm of 1989 served as a

reminder that solar flares can cause widespread

damage, and since then numerous power stations

have taken measures to ensure such an event does

not occur again. “In the past few decades, the grid

has undergone major changes to make it more robu

and better able to neutralise the geomagnetic effect

of solar storms,” a spokeswoman for the Hydro-

Québec power station told us. “Since 1989, solar

activity has not disrupted the performance of Hydr

Québec’s transmission system.”

That, however, does not mean we are safe from

a future huge outburst from the Sun. “We are so

“Right now we’re at the peakof the current solar cycle,although this one has beenpretty uneventful”Joe Kunches, Space Weather Prediction Center

Classifying solarradiation storms

Minor

50 per 11-year solar cycle

25 per cycle

10 per cycle

3 per cycle

Less than 1 per cycle

Moderate

Strong

Severe

Extreme

A minor solar radiation storm causesminimal impact on high-frequency (HF)

radio in the polar regions, but otherwisecauses no damaging effects.

A moderate storm affects navigation at thepolar caps and may, in rare instances, causeproblems in satellites, but poses no threatto humans.

During a strong storm astronauts areadvised to seek shelter, while satellitescould lose power and instrument usage. HFradio will degrade at the poles.

Astronauts and passengers on planes maybe exposed to radiation, while satellitescould experience orientation problems. HFradio blackout at the poles.

Astronauts and aeroplane passengersexposed to high radiation. Satellites maybe rendered useless. HF communicationsblackout in polar regions.


27/180

The Sun

MagnetosphereThe magnetic field lines ofthe Earth’s magnetosphere

divert most of the solarwind around the Earth

InteractionThe incoming sola

particles excitethose in our ownatmosphere, causiauroras at the pole

IonisationThe incoming particles canalso ionise the atmosphere,which can have hazardouseffects on satellites,communications and more

TrappedSome of the chargedparticles are trapped

and guided by theEarth’s magnetic field

Solar space observatories

SOHOThe Solar and Heliospheric Observatory (SOHO)

launched on 2 December 1995 to observe the Sun

from a position between the Earth and the Sun, the

L1 Lagrange point, and it continues to operate today.

A joint project between ESA and NASA, it is currently

the main source of data for space weather predictors.

ACENASA’s Advanced Composition Explorer (ACE) has

been in space since 2 5 August 1997, with its main

goal being to study the composition of solar wind.

Like SOHO it is located at L1, and it is expected to

continue operations until around 2024 when its fuel

will be depleted.

STEREOThese twin spacecraft, known as the Solar

Terrestrial Relations Observatory (STEREO),

launched on 26 October 2006 and, through

their respective solar orbits, they are able to get

stereoscopic images of the entire Sun. This has

proven useful for detecting solar flares.

way to deflect solar flares and not much we can do

a particularly powerful one interacts with the Earth

While we can estimate when a storm will arrive,

determining its power as it travels from the Sun to

the Earth will be of most importance for the future

of predicting solar storms in order to try to minimis

the effects of a large solar flare. “The next big step t

be taken is in the science to better understand the

information that’s available to us now,” said Kunche

“I think that’s the challenge of the next generationof space scientists, to try and understand better tha

we do now which of all the remarkable features we

see back at the Sun are going to be the ones that

really impact the systems we depend on.”

reliant on satellite-based technology, like GPS-based

applications, and you look at them and they’re all

very similar,” Kunches said. “One really couldn’t be a

backup for a nother because they all f ly at about the

same orbits. And then you get to the electrical power

grids and how interconnected they are, and if you

get induced currents that cause transformers to be

damaged and the ripple effects from those could be

quite strong. We rely on infrastructure that is known

to have sensitivities to space weather.” And while the general public may not have much

of an interest in space weather, a large solar storm

would certainly be noticeable to the layman on

Earth. “I think everyone would agree that if you had

a Carrington-like event there’s no doubt that normal

citizens, who have no awareness of space weather

and really don’t care about it, would wake up in

the morning and they would see that something

is different,” said Kunches. “They would find that

something, be it their electricity or their television or

their cell phone, is not available as they wish it to be.”

With space weather prediction agencies like the

SWPC we are able to prepare for the worst when

it comes to solar storms but, ultimately, if a hugeemission event were to occur we don’t have much

of a defence. In extreme cases we can power down

equipment, and prepare our electronic infrastructure

to deal with an increase in energy, but there is no

Deadly solar flare


28/180

28

The Sun

28

The Sun

NASA spots an enormous coronal hole opening upand expanding above the surface of the SunThis image was taken by NASA’s Solar Dynamics

Observatory in mid-June last year. It shows the

electromagnetic activity of the Sun in extreme ultraviolet,

with the colder regions in blue. There’s a remarkabledifference between the hot, dense atmosphere in the

southern hemisphere and the north, which is considerably

cooler. This is because a huge coronal hole has opened

up in the Sun’s atmosphere, around 650,000 kilometres

(400,000 miles) in diameter, or the distance of more than

50 Earths wide.

In this region, solar winds can emerge at furious

velocities, typica lly up to around 800 kilometres per

second (500 miles per second), which is about twice the

speed of solar winds in the regions where the coronal hole

isn’t present. It kicks up a hell of a lot of dust in its wake

too, carrying material from the Sun far out into the Solar

System in every direction.

The holein the Sun As d ramatic as this sounds, coronal holes are actually

a regular part of the Sun’s 11-year cycle, growing larger

and moving closer to the poles the nearer to the solar

maximum we get. The most recent solar maximumoccurred towards the end of 2013, when we saw such huge

coronal holes converging.

During this peak, the Sun’s increase in activity

can affect normal weather patterns on Earth,

telecommunications can be disrupted and solar flares

can get particularly large. In addition, early in 2014 the

Sun’s magnetic field weakened to zero and then flipped,

with mag netic north becoming ma gnetic south and

vice versa , creating solar storms. Incredibly, a huge

solar storm during the maximum of 1859 resulted in the

aurora borealis stretching way beyond its normal limits,

and for a period could be seen as far south as Italy and

the Caribbean.

The Sun, shot in UV in 2010, several years earlier in itscycle and showing no substantial coronal hole


29/180

The hole in the

As it approaches solar maximum, the Sunmagnetic field is about to completely fl

while a huge coronal hole (the big blue patcopens up in its northern hemisphe


30/18030

The Sun

30


31/180

Our local star might seem to be an unchanging ball of blazing light, but in reality its uppe

layers are seething with extreme activitythat varies in a period of around 11 years, and

whose influence reaches as far as Earth

Solar maximum


32/180

“There is acuriosity that is

part of humannature thatmakes us wantto understandhow the Sunand otherstars work”Dr Giuliana de Toma

The Sun is the dominant force

shaping conditions on Earth and

throughout our Solar System – a

brilliant ball of gas powered by

nuclear fusion in its core, whose

influence reaches out across billions

of kilometres. Radiation at both visibleand invisible wavelengths provides

heat and light to the planets, and from

the point of view of a casual observer,

seems more or less constant –

certainly seasonal changes as a planet

moves around its orbit and changes its

orientation and distance from the Sun

have a far greater influence over its

climate than any slight fluctuations in

the Sun’s behaviour.

But nevertheless, these changes

are real – and while they do little

to change the Sun’s heating effect

on Earth, they can be spectacularly

violent in other ways, threatening

orbiting satellites, distant spaceprobes and even reaching down to

the surface of the Earth itself. The

Sun is unpredictable and can produce

extreme outbursts at any time, but in

general, the frequency and intensity

of these events varies in a ‘solar cycle’

of around 11 years. The cycle, as we

shall see, is fundamentally driven

by the Sun’s changing magnetic

field and, through improving their

understanding of it, astronomers hope

to learn more about the deep structure

of all stars.

Dr Giuliana de Toma, a solar

physicist at the National Centerfor Atmospheric Research (NCAR)

in Boulder, Colorado, has made a

career of studying the Sun’s cyclical

behaviour. She puts it this way:

“There is a curiosity that is part of

human nature that makes us want to

understand how the Sun and other

stars work. The Sun is a very special

star, not only because the life on Earth

depends on it, but because the Sun is

the only star that we can observe in

detail. What makes the Sun (and other

active stars) very interesting is the

presence of a magnetic field. One of

the great challenges in solar physics is

to understand, and ultimately predict,

solar magnetic activity.”The solar cycle was first identified

in 1843 by German astronomer

Heinrich Schwabe – the result of a

17-year project to map the number and

size of dark spots on the bright disc

of the Sun. A few years later, Swiss

astronomer Rudolf Wolf used historical

records of these dark sunspots to

trace Schwabe’s cycle back as far as

1745, confirming a period of around 11

years with distinct peaks in sunspot

numbers (solar maxima) separated by

intervening minima.

While it may appear superficially

solid, the Sun’s visible surface, or

photosphere, is in fact a layer a fewhundred kilometres deep marking the

region where the Sun’s gases finally

become transparent a nd allow l ight

and other radiations to escape into

space – temperatures in this region

average approximately 5,500 degrees

Celsius (9,930 degrees Fahrenheit),

but sunspot regions are up to 2,000

degrees Celsius (3,630 degrees

Fahrenheit) cooler, and so appear dark

in comparison.

“Sunspots are regions of strong

magnetic fields that appear dark when

the Sun is observed in visible light,”

says Dr de Toma. “At solar maximumsunspots are more numerous than

at solar minimum. Larger and more

complex sunspots are more commonly

seen near solar maximum.”

But while you might think that

dark spots on the Sun’s surface would

cause its overall energy output to

fall, the opposite is actually the case:

“The Sun’s radiative output peaks at

solar maximum. This seems counter-

The violent SunThe terms solar flare and coronal

mass ejection (CME) are often used

interchangeably, but in reality

they refer to distinctly separate

phenomena. A flare is a huge release

of energy created when magnetic

field lines looping through the solar

corona reconnect or ‘short-circuit’at a lower level. The event heats the

surrounding electrically charged

plasma up to 10 to 20 million degrees

Celsius (18 to 36 million degrees

Fahrenheit) causing it to emit intense

radiation across the electromagnetic

spectrum, and also accelerating

subatomic particles such as protons

and electrons to speeds close to that

of light. These particles escape the

Sun still travelling at tremendous

speed, and give rise to ‘radiation

storms’ as they pass the planets.

Hot spotsPlages and faculae are

bright, hot regions causedby concentrations of

magnetic field around theedge of emerging sunspots

Cutting looseThe CME is preceded by a

magnetic reconnection eventin which the loop of magnetic

field short-circuits closer tothe solar surface, leaving its

upper regions isolated

Rapid expansionFreed from their magnetic

ties to the Sun, gasesin the filament expand

rapidly, blowing outacross the Solar System at

hundreds or thousands ofkilometres per second

While flares have been studied

for over 150 years, CMEs were first

conclusively detected in 1971. They

are usually associated with flares, an

are thought to be generated when

loops of magnetic field ‘cut loose’

by a magnetic reconnect ion, and

the filament material within them,expand violently outwards. CMEs

form billowing clouds of relatively

dense material within the general

‘solar wind’ of particles flowing

out from the Sun, but compared

to radiation storms they travel at

comparatively sedate speeds of a few

hundred kilometres per second. As

a result, they may take days to reach

Earth, but when they do, the magne

field still carried within them can

interact with Earth’s own magnetism

to cause major geomagnetic storms.

32

The Sun

32


33/180

The Sun’s magnetic fieldThe Sun’s magnetic field is believed

to form beneath its visible surface

– specifically in the ‘convective

zone’ extending down to about 0.7

solar radii, where bulk movements

of charged gas bring heat to the

surface. Details of this mechanism,

known as the solar dynamo, are not

certain, but at the start of a cycle it is

capable of generating a fairly orderly

magnetic field whose poles roughly

align to the Sun’s axis of rotation.

Over time, though, the solar interior

experiences ‘differential rotation’,with equatorial regions rotating faster

than high latitudes. As a result, the

magnetic field becomes distorted,

and interactions between different

regions force magnetic loops, the

focus of sunspots and flares, out of

the surface. As the cycle progresses,

some of the magnetic field starts to

cancel out across the equator, while

part is carried towards the poles

where it plays a role in reversing the

magnetic field for the next cycle.

N

S

N

S

N

S

Active centresAs the magnetic field becomes morecomplex, neighbouring field lines startto interact and magnetic loops arepushed out of the photosphere, whilethe overall dipole field becomes weakand more complex.

Differential twistingEquatorial regions of the Sun completeone rotation every 25 days, whilethose at high latitudes may take 30days or more. This differential rotationgradually pulls the Sun’s magnetic fieldout of shape.

TIME TIME

Orderly fieldAt the beginning of a solar cycle, theSun’s magnetic field has a clear andfairly orderly ‘dipole’ arrangement,with magnetic field lines entering andemerging from the Sun’s visible surfaceat high latitudes.

Filament structureCMEs often begin life asfilaments – regions ofrelatively dense gas thatarc along loops of magneticfield in the corona

Magnetic rootsSites where the magnetic field

emerges from and re-entersthe Sun’s visible surface are

marked by sunspots (unseen atthis wavelength)

Solar maximumSolar maximum


34/180

Effectson Earth

AurorasBrilliant northern and southern lightscovered the sky at high latitudes,making the night appear brighterthan a full Moon. Aurorae werevisible across the planet, almostdown to equatorial latitudes

SatellitesA variety of orbiting spacecraft wereaffected, as the storm blocked contact witgeostationary weather satellites for severahours. At lower altitudes, the Space ShuttDiscovery and other satellites reportedfaults and anomalies

Telegraph polesElectric currents induced in overhead wiresgave some telegraph operators electric shocks,while telegraph pylons threw sparks

Ground systemsElectric power networks were not yetin use, but flowing currents in telegraphwires caused some systems to continuesending and receiving signals evenwhen they were switched off

The stormAn enormous CME associated with the Carrington Event created a geomagneticstorm as it swept past Earth, creating strong electromagnetic fields and pushinghuge numbers of particles out of Earth’s radiation belts into the upper atmosphere.

The stormThe CME which caused the 1989 storm wareleased from the Sun on 10 March, a fewdays after a major flare. The storm passed

Earth on 13 March, causing aurorae thatcould be seen as far south as Florida

intuitive, but sunspots are surrounded

by bright features called faculae and

plages that make the Sun brighter at

solar maximum.”

Another aspect of the su nspot cycle,

meanwhile, gives rise to one of the

most iconic diagrams in all of science.

By recording not just the number

and size of sunspots, but also their

latitude on the surface of the Sun,

English astronomer Edward Maunder

discovered a steady drift in latitude

throughout each cycle, with spots first

appearing in small numbers at high

latitudes in each hemisphere, peaking

around mid-latitudes, and dying away

as the remaining spots converged on

the equator. The beautiful symmetric

pattern produced when sunspot

latitudes over a full solar cycle or more

are plotted on a graph is known as a

‘butterfly diagram’.

While sunspot activity is by

far the most obvious indication

of the solar cycle at work, it is far

from being the only one. Since the

beginning of the space age, new

technologies for studying the Sun at

invisible, high-energy wavelengths

such as the ultraviolet and X-rays

have revealed far more spectacular

outbursts that are also linked to

the cycle. “The magnitude of the

solar radiative variation over a solar

cycle is a function of wavelength. In

visible light, the change is very small,

but it is much larger in the shorter

wavelengths of ultraviolet and X-ray

radiation,” outlines Dr de Toma.

Much of this higher-energy radiati

is associated with solar flares – sudde

brightenings of the Sun’s sur face tha

typically last for just a few minutes

but can release enormous amounts

of energy – equivalent to a billion

megatons of TNT. They occur in the

solar corona – the Sun’s thin outer

atmosphere where gas is far more

tenuous than at the photosphere, but

temperatures can soar up to 2 million

degrees Celsius (3.6 million degrees

Fahrenheit), and are often seen

1859

1989

UtilitiesFluctuations in Earth’smagnetic field induced electriccurrents in the crust, which inturn tripped circuit breakersand caused blackouts inQuébec and elsewhere

How solar storms have affected ourevolving technology across history

34

The Sun

34

The Sun


35/180

Ground systemsBeneath Earth’s protectiveatmosphere, ground-based electroniare mostly protected, and vital systemin aircraft and cars also have robustdesigns. However, power networks,by their nature, remain vulnerable topower fluctuations and surges

Hydro-Québec power gridThis major electricity network

covering much of eastern Canadasuffered a complete blackout

and could not be restarted fornine hours. It was particularly

vulnerable due to local geologyand the length of its power lines

ISSAstronauts on the InternationalSpace Station can expect to seetechnical glitches and anomaloureadings, but should be shieldefrom the worst of the radiation,since they are well within Earthmagnetic field

above active sunspot regions. Flares,

too, are thought to be connected to

changes in the Sun’s magnetic field,

specifically ‘reconnection events’ in

which a loop of magnetic field arcing

high into the corona ‘short-circuits’ at

a lower level to release an enormous

amount of energy and a burst of high-

energy radiation. Flares are also often

associated with huge releases of high-

speed subatomic particles known as

coronal mass ejections (CMEs – see

‘Solar flares vs coronal mass ejections’

boxout on page ww). Travelling at

millions of kilometres per hour, the

particles from a CME can reach Earth

within a couple of days.

19th Century scientists puzzled for

some time over the cause of the solar

cycle, but a key breakthrough came

in 1908, when US astronomer George

Ellery Hale made the link between

sunspots and powerful magnetic

fields. Since the Fifties, this has given

rise to a ‘solar dynamo’ theory that

describes how the Sun’s initially

smooth magnetic field, deep beneath

the visible surface, becomes twisted

during each solar cycle by its fluid

rotation, and eventually gives rise to

magnetic loops that push out throug

the photosphere and are associated

with sunspots, flares and other kinds

of activity (see ‘The Sun’s magnetic

The stormWe can expect any future geomagnetic storm to be preceded by one or morepowerful solar flares. Spacecraft such as NASA’s STEREO probes, viewing the Sunfrom different angles, should give a few days’ warning that a CME is on its way.

2014

SatellitesSince the 1989 storm, many lessons

have been learned about satellite design.Electronics are typically ‘radiation

hardened’ to reduce short circuits causedby particle strikes, but some satellites may

have to be shut down and restarted

” A direct hit by a powerful CME can causesignificant disruption to our planet’smagnetic field”

Solar maximum


36/180

field’ boxout on page 33). By the end

of the 11-year cycle, the Sun’s magnetic

field has been converted back to a

simple ‘dipole’ arrangement, but with

its north and south poles reversed, and

the cycle begins again.

However, a detailed understandingof the dynamo remains elusive,

since it relies on an accurate model

of the Sun’s interior. Such models

have only become possible in recent

years thanks to developments in the

field of helioseismology (using sound

waves on the Sun’s surface to map its

structure, just as geologists use seismic

waves to explore our own planet’s

inner layers) and, as a result, many

questions remain unanswered.

A direct hit by a powerful CME ca n

cause significant disruption to our

planet’s magnetic field. This kind of

event, known as a geomagnetic storm,

can send particles pouring into Earth’supper atmosphere where they cause

stunning displays of aurorae (northern

and southern lights). However,

the combination of high-energy

radiation and energetic particles can

also have more serious effects for

modern civilisation, affecting orbiting

spacecraft and even ground-based

power networks.

Perhaps the most famous

geomagnetic storm is the ‘Carrington

Event’ of 1859, associated with a

brilliant flare f irst spotted by Engl ish

astronomer Richard Carrington

on 1 September 1859. The ensuingcoronal mass ejection, travelling at

tremendous speed, reached the Earth

barely a day later, trig gering northern

lights that were visible as far south

as the Caribbean, and bright enough

for people at higher latitudes to read

newspapers in the middle of the

night. As the Earth’s magnetic field

warped under the onslaught, telegraph

systems around the world went

haywire as they were overloaded with

unexpected electric currents.

While both flares and CMEs can

occur throughout the solar cycle,

their frequency and average strength

rises significantly around the solarmaximum (the Carrington Event, for

instance, is acknowledged as the peak

of ‘Solar Cycle 10’). Despite the energies

A history of solar activityTracking solar activity prior to the

last couple of centuries is difficult.

Even after the invention of the

telescope, sunspot records were

patchy at first. Ironically, when

astronomers did begin to collect

consistent observations, it was during

the Maunder Minimum period of thelate 17th Century, when spots were

notably reduced. Long-term rises and

falls in solar activity are known as

grand maxima and grand minima –

the Maunder Minimum was followed

by a spike in activity duri ng the 18th

Century, and the short, sharp Dalton

Minimum between 1790 and 1830.

From 1900 to the present, activity

has been high, during a period called

the Modern Maximum that was at its

most intense in the late 20th Century.

Before 1610, solar activity is even

harder to track directly, since only

the very largest sunspot groups were

seen or recorded with the naked eye.

However in 1976, US astronomer

Jack Eddy demonstrated a direct

link between solar activity and the

quantity of radioactive carbon-14 in

Earth’s atmosphere. Since carbon-14 is

preserved in ancient tree rings, it can

be used as a proxy for solar activity,and studies using this method have

revealed a Medieval Maximum

around 1100 to 1250, bracketed by the

Oort Minimum in the 11th Century,

and the Wolf Minimum from around

1280 to 1340. Intriguingly, just as the

Maunder Minimum seems to coincide

with the ‘Little Ice Age’ across Europe

and North America, the Medieval

Maximum also coincides with a

period of mild North Atlantic climate

known as the Medieval Warm Period.

Could a decline from the current

Modern Maximum lead to another fall

in temperatures?

Maunder MinimumDuring the deepest part of theMaunder Minimum in the late 17thCentury, almost no sunspots wereseen, despite careful studies byexperienced observers such asGian Domenico Cassini.

Dalton MinimumThe Dalton Minimum, between around 1790 and

1830, was a relatively brief period of depressedsolar activity. Global temperatures at the time were

also cooler, but this may have been coincidental.

Modern MaximumThe Modern Maximumbegan around 1914and lasted throughoutthe rest of the 20thCentury, with peaks inthe Fifties and Nineties.The subdued activityseen in the currentSolar Cycle 24 may bea sign that it has nowcome to an end.

involved, Dr de Toma points out that

the total solar irradiance (TSI) – the

amount of solar radiative energy that

reaches the Earth’s upper atmospher

– varies by just 0.1 per cent over a so

cycle, but recent research has shown

that within this overall pattern, solaroutput at different wavelengths can

vary by much greater amounts.

Not all cycles are the same, and

some can be much stronger or

weaker than others. Occasionally,

the cycle can barely be detected at

all, as famously happened during

the ‘Maunder Minimum’, a period of

suppressed sunspot activity lasting

from around 1645 to 1715. This event

famously coincided with a so-called

‘Little Ice Age’ of severe winters acros

northern Europe and North America

and while it’s impossible to know if

TSI fell significantly more at this tim

researchers have recently shown thatlong-term fluctuations in the Sun’s

ultraviolet output could have triggere

changes to the regional climate.

So what of the current solar cycle?

Following strong and well-defined

cycles in the past few decades, Solar

Cycle 24, which officially began in

January 2008, has been somewhat

quiet, but also rather puzzling. High-

latitude spots were slow to appear in

the early months of the cycle, and aft

an active 2011, the Sun surprised mo

experts by slumping back into a lull

rather than building to an anticipated

peak in activity. However, some havespeculated that Cycle 24 might show

a double peak, with another burst of

activity in early 2014.

“This cycle is different from the

recent cycles,” explains Dr de Toma.

“During the space age we have seen

period of high solar activity, but Cycl

24 is a very weak cycle. Such weak

cycles have happened in the past,

but this is the first t ime we have the

opportunity to observe a weak cycle

with modern instrumentation.”

Another intrig uing feature

is that the Sun’s northern and

southern hemispheres seem to be

behaving rather differently: “Thetwo hemispheres are never perfectly

synchronised, but the hemispheric

difference in Cycle 24 is very

“The ensuing CME reachedthe Earth barely a day later,triggering northern lightsthat were visible as far southas the Caribbean”

These twoimages, with

October 2010on the left and

October 2012on the right,

show how theSun becomes

more active as itnears the peakof a solar cycle

36

The Sun


37/180

The solarcycle

19982000As the cycle continued,increasing numbers of bright,complex features appearedin each hemisphere, with theregions of activity graduallymoving towards the equator

2001Cycle 23 peaked between 2000 and2003. In March/April 2001, the Sunreleased huge CMEs and one of themost powerful flares ever recorded

20022004Centres of activity begin to

converge on the equator,forming a broad band of bright

features at low latitudes. TheSun’s overall magnetism starts to

lose its simple ‘dipole’ structure

20052006As masses of magnetisedgas meet at the equator,some start to cancel outand solar activity fadesaway. Other magneticmaterial is carried back tothe poles to regenerate anew dipole field

This sequence of images from NASA’s SOHspacecraft captures an entire solar cycle at extrem

ultraviolet wavelengths, highlighting hot featur

such as flares above the Sun’s visible surfa

19961997At the start of Solar Cycle 23, the Sun’sappearance was almost uniformly dark,with just a few bright hotspots of magneticactivity at relatively high latitudes

pronounced. Most of the activity at

the beginning of the cycle was in the

north, while now it is in the south.”

Indeed, the strange features of Cycle

24 illustrate the difficulty of making

predictions about the Sun’s behaviour,

as Dr de Toma points out: “Cycle 24

was the first time that physical models

of the Sun were used to predict a

solar cycle. Before that, the solar cycle

strength was usually predicted using

simple correlations between sunspot

numbers and other solar activity

proxies, or by extrapolating recent

solar behaviour into the future. Solarcycle models are still relatively simple,

and in spite of the progress in recent

years in modelling the solar cycle as

a hydromagnetic dynamo process,

we still do not have a realistic solar

dynamo model. This is an area where

I expect a lot of progress in the future,

both in terms of improving the models

and of obtaining new observations to

better constrain them.”

The weakness of Solar Cycle 24 has

even inspired some solar physicists

to suggest that we might be on the

Experts at the Space Weather Center at NASA’sGoddard Space Flight Center track solar

disruptions to predict their impact on Earth

Solar maximum


38/180

Weatheringstormsfrom spaceProfessor Mike Hapgood explainshow solar storms can affect Earth

What are the various ways solar

activity can influence Earth?Well space weather, like weather

on Earth, is very diverse. We have

geomagnetic storms that are caused

by the solar wi nd coming out from

the Sun, and they have a lot of

diverse effects all over the Earth

including changes to the upper

atmosphere, changes in the magneti

field that affect power grids, and

changes in the environment in near

Earth space that affect spacecraft

and so on. But we also have radiatio

storms – which are related, but a

Solar weather can have

an adverse effect on

satellites in Earth orbit

What is asunspot?Sunspots are dark patches of less

dense, relatively cool material.They form where loops of the solar

magnetic field emerge from and

re-enter the visible photosphere – the

magnetic field opens up a ‘clearing’

that can be up to 2,000 degrees

Celsius (3,630 degrees Fahrenheit)

cooler than its surroundings. For

this reason, spots or groups of spots

usually come in pairs, with a leading

and a trailing spot of opposite

magnetic polarities. The leading spots

in a given hemisphere always have the

same polarity as the general magnetic

field of the hemisphere itself, and lie

closer to the equator. A dark central

region known as the umbra shows

where the magnetic field lines emerge

vertically out of the photosphere, while

a less intense penumbra marks the

surrounding area where the magnetic

field lines are tilted and their cooling

influence is weaker.

Leading spotThe ‘leading’ sunspot liescloser to the equator andhas the same polarity to thehemisphere in which it lies.Magnetic field lines emerging

through the photosphereforce open a low-density‘clearing’ in the Sun’s gases

Trailing spotThe trailing spot is usuallysmaller than the leading spot,and often more complex instructure. Both spots aredepressed in relation to thesurrounding photosphere

Fine structureThe Sun’s photosphereis covered with fine cellscalled granules. Within thepenumbral region, they aredistorted by angled lines ofmagnetic field

Professor Mike Hapgood is headof the Space Environment Group

at the Rutherford AppletonLaboratory in Oxfordshire. As an

internationally recognised expert inthe eld of ‘space weather’, he has adeep interest in understanding the

practical impacts of solar activity onour planet and its technology.

INTERVIEW BIO

38

The Sun


39/180

quite different phenomenon – and

then there are also X-ray and radio

flashes – bursts of radiation that have

different effects. There’s a whole grab-

bag of environmental phenomena,

and these have all sorts of effects on various systems.

What are radiation storms?

These are particles that are

accelerated to very high speeds and

energies. What we call the ‘solar wind’

is the average flow of particles coming

out from the Sun, and while it might

be average, it can still be moving at

hundreds or thousands of kilometres

per second. But radiation storms

involve particles travelling very

close to the speed of light – almost a

thousand times faster. Light travels

from the Sun to the Earth in a little

over eight minutes, and radiationstorms are not much slower, while

the solar wind can take a day to three

days to reach the Earth. Because

they’re travelling much faster,

radiation storm particles can do more

damage – they can penetrate quite

deeply into spacecraft electronics, and

enter Earth’s atmosphere to produce

neutrons in the stratosphere. They

produce quite detectable levels of

radiation at aircraft altitudes, and

when there’s a really big burst we can

even detect it on the ground.

How much danger is there to

satellites in Earth orbit?

Geostationary satellites are by far the

most exposed – they’re orbiting in

the outer parts of Earth’s magnetic

field and get almost no protection,so they have to endure a lot of solar

radiation. The key is good design – on

computer chips for instance, a lot of

the challenge is about very careful

layout of the circuit, and maybe not

putting quite so much on the chip as

a whole. If you’re drawing all these

tiny electrical circuits what you don’t

want is a situation where a radiation

hit could cause a short circuit.

What influence can solar storms

have on ground-based electronics?

Well once again, the key is good

design – if the engineers are aware of

it, they can deal with it, and there’s alot of good work already being done.

For instance, aircraft are already very

robust to such issues, and even cars

are designed with this in mind – you

can hardly warn people not to drive

their cars today because there might

be a solar rad iation storm.

What about the risk of another

Québec-style incident?

Well that’s a very different effect, and

that comes from the geomagnetic

storms. Part of what they do is

cusp of a new long-term minimum

in sunspot numbers. In 2010,

astronomers from the National Solar

Observatory at Kitt Peak, Arizona,

reported evidence for a steady decline

in the strength of the magnetic fields

associated with sunspots over severaldecades, perhaps leading to a new

Maunder Minimum. Dr de Toma,

however, disagrees: “Solar activity has

been weak lately, but t his does not

make Solar Cycle 24 anomalous. We

had weak cycles before, for example

at the beginning of the 20th Century,

without going into a Maunder

Minimum. We still do not know how

and why the Sun went into a Maunder

Minimum, so we cannot predict one.”

What’s more, according to recent

research by Dr de Toma’s group at

NCAR and colleagues at California

State University, Northridge, the

sunspot claims may not stack up:“These observations are very accurate,

but the dataset suffers by serious

selection effects with only a very

few observations taken near the

beginning. Many have questioned

these results, and they have not been

confirmed by other observations.” Dr

de Toma herself was at the forefront of

one effort to crosscheck the evidence,

using detailed sunspot records from

the San Fernando Observatory dating

back to 1986 in a search for long-term

changes. “We did not find that spots

are becoming less dark over time,” sheexplains. “The original researchers

found a decrease in sunspot darkness

of about two per cent each year, but

we found a less than three per cent

change across the entire 27-year span

of the SFO observations.”

Nevertheless, it now seems quite

likely that the Sun does indeed have

longer activity cycles modulating the

11-year sunspot pattern. “There were

weak solar cycles at the beginning of

the 1800s and 1900s. We still do not

know for sure if there is a 100-year

modulation in solar activity, but this is

a very interesting idea.”

One thing is for certain, however– the Sun and its various cycles will

continue to influence everything from

technology to climate. We can do

nothing to influence our local star, so

we must learn to at least understand

it more accurately, and be prepared for

its occasional outbursts of violence.

disrupt the natural electric currents

that flow around the planet. It’s

the fluctuations in the current that

create changes in the magnetic

field, and that in turn can produce

electric currents through Earth’scrust. Those currents can get into

things like power grids through the

earth connections, and if they get

too big, they can upset the operation

of transformers. This can produce

heating, vibration and, in the worst

case, do serious physical damage –

but more li kely the grid collapse s

and they have to do a ‘black start’,

restarting the grid with the power

completely off. That’s something

that’s very heavily rehearsed, but

of course even having the grid off

for a few hours would be a major

disruption. The power grid is the

fundamental infrastructure of modernsociety, and if it’s not there then that’s

a real problem – but we should be able

to cope with other forms of heating

and lighting for a few hours.

Some people have warned about

the risk of a big event in the fairly

near future?

Well it’s always hard to predict – the

big events ca n happen any time in a

solar cycle and we prefer to talk abouonce-in-a-hundred-year risks. It’s not

a good idea to assume that you’re

safe from a major event just because

it’s solar minimum, though it might

be a bit less l ikely. Fortunately the

Sun’s been very quiet for most of the

past few years. On 23 July 2012 there

was a very la rge event, but that wen

off behind the Sun and there’s a lot

of research into what the effects on

Earth might have been if we had bee

in the way.

Finally, we guess that one positive

side effect of these major storms

for skywatchers would be somespectacular aurorae?

Well that’s certainly true – though

they might just have to watch them

with al l the lights out!

The Solar Max satellite, inoperation from 1980 to 1989

was one of the first spacecraft toclosely study solar cycles

“It’s not a good idea toassume that you’re safe froma major event just becauseit’s solar minimum”

Solar maximum


40/180

42 M

all about space book of the solar system - 2014

Documents