AstronomyContents of the universe

We live in the solar system. Earth orbits the sun every yr in

elliptical orbit.Distance Earth to sun 1 AU

Birth of the Solar SystemSolar system born ~4.5 BYA

2 min

http://www.youtube.com/watch?v=qfdDWdZcpOw

Our Solar Systemplanets/moons/asteriods

Asteroid Belt mars-Jupiter

Icy Comets-All orbit the sun

-very elliptical orbits

Solar system is part of the milky way galaxy. Orion Arm.

The galaxy revolves around black hole. Sun revolution ~ 250 million y.

Galaxies –large aggregates of stars, gas, & dust containing ~ 100 billion (1011) stars ranging in diameter from 1,500 to 300,000 light-years across. Orbit central point. Av distance btw stars 10 ly.

Stars can form stellar clusters w/i galaxies – smaller groups of stars held by gravity. ~ 1000’s of stars.

Constellations – star groups not necessarily near each other.

Galaxies form groups too.Galactic Clusters

• Nearest cluster = Virgo cluster

It’s a long way btw stars.Use Light Years LY Calculate the d light travels in 1 yr.

1 LY = 9.46 x 10 15 m.

Relative DistancesUniverse ~1.5 x 1026 m

15 Billion LY

Between galactic clusters ~10 8 LY

Betw galaxies ~106 LY

Local group (20 gal) 2 x 106 LYradius

Milky Way 105 LY dia, 104 LY thick10 LY btw stars

Powers of 10 Film

http://www.youtube.com/watch?v=tnhken4_-A0

Earth’s Rotation makes stars appear to rotate on fixed

sphere.

Rotation is around Polaris on 24 h cycle.

Sun/planets wander through stellar backdrop.

From Earth Stars Appear to be embedded in sphere.

Stars rotate around Polaris24 hr cycle rise east set west

Stars appear fixed on sphere relative to each other.

http://www.youtube.com/watch?v=JCr_Pz4h2Bw

Planetary Motion Wanderer & Retrograde

Hwk Sheet: Intro to Astrophysics