Chapter 1

Speed of light

- 3 x 105 km/s - 3 x 108 m/s - 1,080,000 km/hour - 186,000 miles/second

How many meters in a light year?

- 60 seconds in 1 minute - 3 x 105 km/s x 60 s/min = 1.80 x 10^7 km/min - 60 minutes in 1 hour - 1.80 x 107 km/min x 60 min/hour = 1.08 x 109 km/hour - 24 hours in a day - 1.08 x 109 km/hour x 24 hour/day = 2.592 x 1010 km/day - 365.24 days in a year - 2.592 x 1014 km/day x 365.24 day/year = 9.46 x 1012 km/year - 1 LY = 9.46 x 1012 km (about 6 trillion miles!!)

Eagle Nebula

- 7,000 LY away - Within our Galaxy - Tallest pillar is about one light year long

Saturn

- 9.5 AU from Sun - Diameter = 9.5 x Diameter of Earth

Planet Earth

- About 13,000 km (8,000 miles) in diameter - Liquid water covers 2/3 of its surface - Supports life - One natural satellite o The moon

Light Years

- Astronomers use a convenient unit called "light-year" to describe distances in the universe - One Light-year o Noted 1 LY o Equals the distance that light travels in one year - Useful unit because o Light always travels at the same speed o Highest speed anything can travel through space o Makes for a good standard to keep tract of distances - Light travels 3 x 105 km/s (1 km = 0.6 mile).

Earth's moon

- Diameter is 3,476 km - 2,000 miles - 1/4 the diameter of the Earth - Moon to Earth distance is about 30 times the Earth's diameter - Light travels from the Earth to the moon in 1.3 seconds

Distances in the Solar System

- Distance from Earth to Sun: o About 150 million km (93 million miles) o Defines a unit of distance called an astronomical unit Note: 1 astronomical unit = 1 AU Used for distances within the solar system - Earth revolves around the Sun o Period about 3 x 107 s (1 year). - Speed of revolution: o Earth travels at approximately 110,000 km/hour (18.6 miles/second) in its orbit around the Sun - Light takes 8 minutes to travel from the Sun to the Earth o Our latest news from the Sun is always 8 minutes old

Numbers in Astronomy

- Distance in astronomy are huge - Use power-of-ten-notation o Sometimes called scientific notation - Examples o $5,200,000 = $5.2 Million = $5.2 x 10^6 o 0.000125 = 1.25 x 10^-4

Solar System

- Earth is one of eight major planets orbiting around the Sun that form the Solar System; Pluto as a dwarf planet -formed 4.6 billion years ago - Planet o A body of significant size that orbits a star and does not produce its own light - Star o Large body which (at some point during its life) produces light by nuclear reactions

How we learn about distant objects

- Information about distance objects comes to us via electromagnetic radiation o Light is one form of radiation among others - All such radiation travel at the speed of light o All radiation travels one LY per year

Jupiter

- Largest planet - Diameter o 143,000 km o 11 times the diameter of earth - Distance to Sun o 5 AU - Like many other planets, it has many natural satellites or moons

Local groups of galaxies

- M31 is part of a small cluster of over 400 galaxies called local group - At distances of about 10 to 15 million LY, one finds other small galaxy groups or clusters- Our local group and the Virgo cluster are part of one such supercluster which stretches over a diameter of 60 million LY - Farthest galaxy (red object) o 1.3 x 1010 LY - Galaxies o collections of ~ 1011 stars - Andromeda galaxy o distance 2 x 106 LY - nearest star o 4.3 LY = 9.6 x 1012 km o = 64,000 AU - Sun o 1 AU = 1.5 x 108 km

Planets (closest to farthest)

- Mercury - Venus - Earth - Mars - Jupiter - Saturn - Uranus - Neptune (My Very Evil Master Just Said Ur Next)

Beyond the Milky Way

- Our galaxy is not unique - Most are at enormous distances - Nearest large galaxy is Andromeda, or M31

Far Away and Long ago

- Sets a limit on how quickly we can learn about events in the Universe o If a star is 10 LY away, the light we see from it tonight left that star 10 years ago o If that star exploded today, we would learn about it only 10 years from now

Sun

- Star at the center of our solar system - Diameter: 1.5 million km - Typical size of a star -100 times larger than the diameter of the Earth

Milky Way

- Sun is ~ 30,000 LY from the center of our Galaxy. - From our location within the galaxy, we cannot see through to its far rim because the space between stars is not empty o interstellar dust or gas which absorbs visible light. - The interstellar gas is the substance that permits the formation of stars. - Yet, interstellar material is very sparse; the space between stars is quite empty o much more so than the best vacuum one can achieve in the laboratory on Earth. - Possibility of dark matter. - Star Clusters o contain up to hundreds of thousands of stars - light years across. - Star have a long life (billions of years) but not infinite o they die or collapse in spectacular ways.

AU

-Astronomical Unit -average distance from the Earth to the Sun

Virgo clusters

o At about 50 million LY, one finds a very large cluster containing thousands of galaxies

Super Clusters

o Some of the observed clusters