Survey of the Universe

Tom Burbinetburbine@amherst.edu

Readings

• Should start reading Units 1-4

Stellarium

• Everybody should download the program Stellarium

• http://www.stellarium.org/

• Need to change your location

Office Hours

• M-W 10-11 am in Kendade 221

Help Sessions

• 7-10 pm on Sundays and Tuesdays

• First Help Session will be Feb. 3 in Kendade (email on room number later)

HW #1

• HW #1 is due Feb. 6

Stars

• Stars are composed primarily of Hydrogen and Helium

• Generate energy through nuclear fusion

Sun

• Our star

• Typical star since the msses of stars range from 0.1 to 100 solar masses

• 1 solar mass is the mass of the Sun

http://www.aerospaceguide.net/solar_system/sun.html

Stellar evolution

• Stars are born

• Live

• And then die

Galaxies

• Galaxies are massive gravitationally bound systems of stars and stellar remnants, gas, dust, planets, and dark matter

• Dark matter is matter that you can’t see but whose gravity affects visible matter and background radiation

Milky Way Galaxy

• Our Galaxy

• 100-400 billion stars

http://www.astro.keele.ac.uk/workx/milkyway/page.html

Galaxies• Taken over 11 days

• Over 10,000 objects apparent (majority are galaxies)

• There are estimated to be more than 176 billion galaxies in the observable universe

Light-year

• Distance that light travels in a year

• Light travels at a speed of 300,000,000 m/s in a vacuum

• 1 light year = 10,000,000,000,000,000 meters

Local Group

• Gravitationally bound group of galaxies that the Milky Way is a member of

• Contains more than 30 galaxies

http://hendrix2.uoregon.edu/~imamura/123/lecture-3/lecture-3.html

Big Bang

• Explosion that started the Universe

Why do we use the metric system in science?

• A system based on multiples of 10 is much more intuitive for humans

• We are born with 10 fingers and toes

• The math system that we use is based on 10

Metric System

• Any system of measurement needs three fundamental units– Length - meter– Mass - kilogram– Time - second

• 1 kilometer = 1,000 meters

• 1 meter = 100 centimeters

• 1 centimeter = 10 millimeters

• 1 kilogram = 1,000 grams

Things you need to know because we will use the metric system

• one kilometer is 5/8 of a mile

• one meter is 3.28 feet

• one centimeter is 0.39 inches

• 1 kg (mass) is equivalent to 2.2 pounds (force) on Earth

• We will use the metric system in this class

• Does anybody remember the Mars Climate Orbiter?

Mars Climate Orbiter• Software calculated forces for the

thrusters in English units (pounds). • People controlling the spacecraft thought

the calculated forces were in Newtons (metric). (One English pound of force equals 4.45 Newtons.)

• Changes made to the spacecraft's trajectory were actually 4.45 times greater than what the JPL navigation team believed.

• The spacecraft missed its intended 140 - 150 km altitude above Mars during orbit insertion, instead entering the Martian atmosphere at about 57 km.

• The spacecraft was destroyedhttp://en.wikipedia.org/wiki/Image:Mars_Climate_Orbiter_2.jpg

• 1 kilometer = 1,000 meters

• 1 meter = 100 centimeters

• 1 centimeter = 10 millimeters

• 1 kilogram = 1,000 grams

• one kilometer is 5/8 of a mile

• one meter is 3.28 feet

• 1 kg (mass) is equivalent to 2.2 pounds (force) on Earth

Meter

• How is the meter defined?

Meter

• Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole

• International Prototype Meter was defined as the distance between two lines on a standard bar composed of an alloy of ninety percent platinum and ten percent iridium, measured at the melting point of ice.

Meter

• Now defined as equal to the distance travelled by light in vacuum during a time interval of 1⁄299,792,458 of a second.

Gram and Kilogram

• How are the gram and kilogram defined?

Gram and Kilogram

• How are the gram and kilogram defined?

Gram and Kilogram• A gram was first decreed to be equal to “the absolute

weight of a volume of water equal to the cube of the hundredth part of the meter, at the temperature of melting ice.”

• Now, the International Prototype Kilogram is used as the standard.

• It is made of a platinum alloy known as “Pt‑10Ir”, which is 90% platinum and 10% iridium

International Prototype Kilogram

• Photo of Danish national

kilogram prototype

Other Units used in Astronomy

• Solar mass – Mass of Sun

• Jupiter mass – Mass of Jupiter

• Light year – Distance light travels in a year

• Astronomical Unit – Average distance between the Sun and the Earth

• Speed of light (c) - 3 x 108 m/s

Scientific Notation

• 10000 = 104

• 100000000 = 108

• 10000000000 = 1010

• 100000000000000000000 = 1020

• 0.001 = 10-3

• 0.0000001 = 10-7

How do you write numbers?

• 31,700,000 = 3.17 x 107

• 2,770,000 = 2.77 x 106

• 0.00056 = 5.6 x 10-4

• 0.0000078 = 7.8 x 10-6

How do you do multiply?

• 106 x 108 = 10(6+8) = 1014

• 10-5 x 103 = 10(-5+3) = 10-2

• (3 x 104 ) x (4 x 105) = 12 x 10(4+5) = 12 x 109 = 1.2 x 1010

How do you divide?

• 108/106 = 10(8-6) = 102

• 10-6/10-4 = 10(-6-(-4)) = 10-2

• (3 x 108)/(4 x 103) = ¾ x 10(8-3) = 0.75 x 105 = 7.5 x 104

Always use units for your answers

Stars in the Universe

• Say there are 100 billion galaxies

• Each galaxy has 100 billion stars

• So how many stars in the universe

Answer

• Number of stars in universe

• = (100 x 109) x (100 x 109) = 10000 x 1018

= 1 x 1022 = 10,000,000,000,000,000,000,000

• This is about the same number of grains of sand in every beach in the world

Questions:

• How many of these 1022 stars have planets?

• How many of these planets have life?

Any Questions?