Chapter 1.1-1.2 1.3-1.4

Front 1

galaxy clusters

Back 1

groups of galaxys with more than a few dozen members

Front 2

Milky Way Galaxy

Back 2

a great island of stars in space

realatively large galaxy, containing more than 100 billion stars.

Located a little over halfway from the center to the edge of the galactic diski

Front 3

How are galaxies and galaxy clusters arranged? What are superclusters?

Back 3

they appear in giant chains and sheets with huge voids between them. Superclusters are the regions in which galaxies and galaxy clusters are most tightly packed.

Front 4

What is the universe?

Back 4

the univers is the sum total of all matter and energy, encompassing the superclusters and voids and everything within them.

Front 5

What are two astronomical distance measurements? Describe.

Back 5

AU- is Earth's average distance from the sun, which is about 150 million kilometers. Commonly used.

Light Year- the distance that light can travel in 1 year, which is about 10 trillion kilometers (6 trillion miles) used to describe the distances of stars and galaxies. We measure in light years because light from stars takes ~8 years to reach us.

Front 6

Speed of light

Back 6

So fast that it could travel earth nearly eight times in a single second. takes one second to reach earth from the moon and 8 minutes to reach earth from the sun.

the farther away we look in disance the further back we look in time -- pg 4. We see stars in the sky as they looked the amount of years ago it takes their light to travel to earth.

when we study the universe it is impossible to seperate space and time.

Front 7

How old do astronomers estimate the earth is? why?

Back 7

14 billion. 14 billion years marks the horizon of our observable universe. since we cannot see anything past 14 billion light years away we deduct that 14 billion years ago the earth must have been conceived.

Front 8

What is the Voyage model?

Back 8

It is a model of our solar system that shows the planets along a straight path.

shows planets and the sun at one 10-billianth of their actual sizes and distances. The sun is about the size of a large grapefruit, jupiter a marbel, earth the ball of a pen. The moon lies only about 4 cm from earth in the voyager model.

Front 9

Space looks empty why?

Back 9

Because only the sun, our moon, and a few planets are big enought to see. the rest looks virtually empty because other matters are so small.

Front 10

On the voyager model how close is the nearest star system, what is it?

Back 10

Alpha centauri, which is about 4.4 light years away. that distance is about 4400 kilometers on the 1-10 billion scale. Roughly equivilant to the distance across the united states.