Astronomy, Stars and Galaxies (2019)

1. Introduction to Astronomy

Humans have been fascinated by objects in the sky for thousands of years.

Different cultures developed different explanations for the existence of

cosmological objects, how they formed, and our place in the universe. The

understanding of the Earth's place in the universe improved over time as humans

become more scientifically advanced. Better instruments allow scientists to make

better observations leading to better models of the earth-sun relationship. The

most popular model and the model you are probably most familiar with is the

Copernican Model show below:

Astronomy is not to be confused with astrology. Astronomy is based on theories

and hypothesis. On the other hand astrology is based on the premise that the

date of birth defines the kind of person you are.

https://youtu.be/FmGBS1Q91RI

Big Bang Theory The most current theory of how the Universe formed is called the Big Bang

Theory which hypothesized that all matter and energy was compressed into one

tiny mass. In one instance the original mass exploded spewing subatomic

particles, and unleashing the four fundamental forces (gravity, strong nuclear

force, weak nuclear force, and electromagnetism) into the space. Within a very

short period of time after the explosion matter moved incredibly high speed to fill

the empty space. As time passes the subatomic particles combined and interact

with each other via the four fundamental forces to form new atoms, stellar

matter, stars, solar systems, and galaxies to occupy the Universe.

Evidence of the Big Bang

The Big Bang Theory is supported by observations. Firstly, the

electro-magnetic energy of quasars is highly red-shifted, as is the light from all

galaxies outside our local group. This red-shift caused Edwin Hubble to rightly

conclude that all galaxies are moving apart, and that the universe is

expanding. Scientists conclude that if all galaxies are moving apart today, then

at some point in the past they were all together.

Secondly, there is ambient level of cosmic radiation that seems be uniformly

spread out in space. Presumably this is the left over of the energy resulting

from the explosion.

Future of the Universe

What the future holds for the universe depends on the balance or competition

between gravity (pulling the universe back in) and momentum (pulling the

universe outwards):

● If the force of gravity wins then the universe is said to be "closed" and

will collapse in what some call the "Big Crunch". This could potentially

lead to a second Big Bang and Big Crunch, repeating forever in what is

called the Oscillating Universe Theory. It is possible that the most recent

Big Bang is not even the first, it could be anywhere from the first to the

43rd billionth!

● If momentum of the galaxies exceeds gravity's ability to slow, stop and

reverse them then the universe is said to be "open" and will expand

forever.

https://youtu.be/sZ59mBnWUEY

3. Studying the Universe

Astronomy would not be possible without scientific observations

made using the naked eyes. Civilizations throughout human

history have used these observations to record the passage of

time and to predict future cosmological events. As scientific

knowledge and technology improve, our understanding of the

properties of the cosmos also improve which helps us to

appreciate our place in the universe.

In this chapter you will be looking at various instruments that

help astronomer study the cosmos.

Optical Telescopes

Telescopes: Eyes to the Universe

Observing stars is done with many instruments. The most popular of which is an optical telescope. Optical

telescopes extends the power of the human eye as it gathers light from cosmological objects, resolves it, and

magnifies it making objects from outer space appear bright, in high contrast, and as large as possible.

Read about the

● history of the telescope.

https://www.nasa.gov/audience/forstudents/9-12/features/telescope_feature_912.html

● the locations of the world's largest optical telescopes.

https://en.wikipedia.org/wiki/List_of_largest_optical_reflecting_telescopes

●

Types of Telescopes

Optical telescopes are classified as refractors or reflectors. Each uses the properties of light and it interaction

with mirrors and lens to bring images of distant object to observable range.

Refractors:

Refractor telescopes make use of lenses to collect light and magnify it

The refracting telescope is basically a tube with a lens on each end as shown in the

link below, each part is important and you should be able to describe the shape

and purpose of each part. Some important notes are included with the diagram so

be sure to read those through.

Reflectors:

Reflector telescopes use mirrors to collect light and lenses to magnify it

A reflecting telescope uses two mirrors in its tube to collect and bend light. Again

a diagram is provided and you are responsible to determine the parts.

Because of the high cost of making perfect mirrors, and any tiny flaw will make the objective in a reflector

useless, many new telescopes use many smaller mirrors to collect the light. These are known as MMT or

multiple mirror telescopes. Each smaller mirror is specially shaped to collect the light and reflect it to the

same focal point. The main advantage is an enormous cost savings on making more small mirrors rather than

one big one.

Maximizing telescope clarity

Various conditions are required for an optical telescope to operate

well; as a result only certain locations are good for placing an

optical telescope. Some of the conditions include: stable night

temperatures, clear weather or being above the weather, far from

the background light of cities and as little atmosphere to block

the light from stars as is possible. As a rule high mountains and

deserts make good locations for optical telescopes.

Hubble Telescope

The Hubble Space Telescope is capable of viewing all wavelengths

and is stationed in orbit around the earth. Because it is in space

its temperature is constant, there is no light pollution in image

from cities, no light is blocked by cloud, no light is absorbed by

the atmosphere and it is always able to point to night somewhere

in space. The Hubble gives excellent image all day every day.

While it is nearing the end of its useful lifetime new technology

will see us one day place a new observational satellite in space

and on the International Space Station.

https://youtu.be/joDtVFGa1-g

Radio Telescopes

Need for Radio Telescopes

Notice that visible light is a very very narrow band of the full electromagnetic

spectrum. Using optical telescopes only, astronomer would miss out on a HUGE

amount of information emitting from stars, galaxies in the non-visible range.

Additionally, a star's maximum brightness is based on temperature. As energy

increases in a star its temperature also increase causing its brightness to increase

as well. However, a star's brightness only shows the visible wavelengths of the

EM. Besides visible light, stars also emit EM waves NOT in the visible range

A radio telescope detects the radio waves given off by stars

and can "see" things our eyes can't. Radio waves can pass

through the atmosphere easily. Unlike visible light which is

lost in daylight, radio waves can be measured 24 hours per

day. Radio telescopes are satellite dishes which collect radio

waves given off by stars and galaxies.

Radio Telescope Array

A radio telescopic array makes use of many satellite dishes

over a long baseline but the multiple dishes can make for a

clearer image. Other telescopes that collect and view X-rays,

gamma rays, infra-red and ultra-violet rays but are not used

on the surface of the Earth due to absorption of these waves

by the atmosphere.

3.3. Other Instruments

Non Optical Telescopes

The Electromagnetic Spectrum

Visible light is characterized by its energy, wavelength and frequency. Light is

only a small part of what is known as the electromagnetic, or EM, spectrum.

Other forms of electromagnetic waves are not visible to human eyes. Some

you may have heard of such as infra-red, ultraviolet, microwaves and X-rays.

The EM spectrum diagram below shows the energy, frequency and

wavelength of each type of EM wave.

All stars produce light. Using a spectroscope to observe their spectra closely

we see dark lines. These are caused by specific elements in the star absorbing

energy at certain wavelengths. Looking closely at the dark lines and their

wavelength we can determine what sort of elements are in the star. Spectra

with dark lines are called absorption spectrum as the light from the spectrum

has been absorbed (leaving black lines) at certain wavelengths. An example of

the absorption spectrum of a gas is below.

Astronomers take the absorption spectra and compares it the emission

spectra to determine the elements in the star.

This is the absorption spectra of

a star which has an unknown

element.

The absorption spectra is

compared to this emission

spectra of a known element.

Using this comparison

astronomers can determine the

elements in the star.

The Spectroscope

You have probably seen a picture similar to one below in which white light is pass through a prism which

breaks down visible white light into seven bands of colours. Astronomers use this principle in an instrument

called the spectroscope to determine the elements in a star.

Emission Spectrum

All atoms and elements will emit light when they are highly energized. Viewed through a spectroscope,

the light generate a pattern called an emission spectrum. Each element will generate a unique emission

spectrum.

In the lab supercharged gases to generate a emission spectrum. The diagram below shows the emission

(bright line) spectra of hydrogen, sodium, helium, neon and mercury.

Absorption Spectrum

All stars produce light. Using a spectroscope to observe their spectra closely we see dark lines. These

are caused by specific elements in the star absorbing energy at certain wavelengths. Looking closely at

the dark lines and their wavelength we can determine what sort of elements are in the star. Spectra

with dark lines are called absorption spectrum as the light from the spectrum has been absorbed

(leaving black lines) at certain wavelengths. An example of the absorption spectrum of a gas is below.

Astronomers take the absorption spectra and compares it the emission spectra to determine the

elements in the star.

This is the absorption spectra of a

star which has an unknown

element.

The absorption spectra is

compared to this emission spectra

of a known element.

Using this comparison astronomers

can determine the elements in the

star.

Cameras

Cameras and CCD (charge coupled devices) are used

to capture film and digital images of stars for later

study. They can also be used to determine

variations in brightness and position from hour to

hour or night to night. A digital camera set on a

time long exposure can capture star trails.

Blue and Red Shifting

We know when a sound source is moving towards or away from us its volume changes. We also know that its pitch changes in a phenomena call The Doppler Effect. Light exhibit a similar

behavior called Blue shifting or Red shifting.

You'll learn more about these later on.

https://youtu.be/Kg9F5pN5tlI

3.4. Modern Space Exploration

In 1957 Sputnik I was the first artificial satellite launched into space by the USSR.

The satellite was small, battery powered and could barely manage to send a radio

signal back to Earth. Later that same year the USSR sent the first dog, Laika, into

space on Sputnik II. In 1958 Gordo the monkey was launched by the USA into

space aboard a rocket. Unfortunately when his craft landed in the ocean it sank

and Gordo was never to be seen again. 1959 saw the USSR send an unmanned

rocket around the Moon and brought back the first images of the far side (recall

from last lesson that the same side always faces Earth).

Human's first ventured into space was in 1961 when the USSR sent Yuri Gagarin

around the Earth in a rocket. The early 1960's saw several unoccupied probes land

on the moon, the first woman in space. In 1967 the USSR landed Venera probes

on Venus, sending back images of Venus beneath the clouds. 1969 saw the USA

successfully land Neil Armstrong and Buzz Aldrin of the Apollo 11 mission on the

surface of the moon. Budgetary cut backs in both the USSR and USA saw space

exploration slow to a crawl but the two countries staged joint meetings and

research on Skylab and Salyut space stations in orbit.

During the late 1970's and 1980's space research focused on launching

communication satellites, spy satellites, and research into space based weaponry.

The invention of the space shuttle changed the path of exploration by allowing

re-usable spacecraft and rockets to drop costs and re-initiate opportunity.

Satellites were used to carefully map and measure the Earth. With increasing

ultraviolet, infra-red, and radio wave technologies in the EM spectrum we were

able to look at and view the Earth differently from above.

The invention of the Global Positioning System, GPS, by the US military in the

1990's was made possible with the use of 24 satellites in fixed orbits above the

earth. Any ships, aircraft, tanks, personnel and supplies across the surface of the

Earth with a GPS transponder can calculate its distance from any 3 satellite. Then,

comparing the three measurements it can locate itself on Earth's surface to within

2 meters.

Most recent advances include the Mars rovers, unmanned, robotic explorers we

have landed on Mars, the Cassini and Huygens probes for studying Jupiter, the

Hubble Space Telescope, satellite probes showing desertification, ozone layer

holes, weather systems, hurricane structure, carrying telephone and television

signals to name a few.

Space exploration is not without risk. Financially, billions of dollars every year

from many governments around the world are spent on telescopes, rockets,

space stations, astronaut training, probes etc. Additionally, 21 people have lost

their lives over a period of 50 years. Notably, in the 1967 Apollo 1 disaster, a fire

onboard the rocket killed three USA Apollo astronauts. Then in 1986 the space

shuttle Challenger blew up when it launched, killing the seven astronauts aboard.

https://youtu.be/4s4AlG44EKc