Galaxies shaped round, like a ball, or oval, like an egg and vary greatly in size. Contain billions of stars, but have little gas and dust between the stars, so stars or no longer forming. Only old stars.
Galaxies with a bulge in the middle and arms spiraling outward, like a pinwheel. Spiral arms contain many bright, young stars as well as gas and dust. Very few stars are forming in the bulge.
Galaxies with no regular shape. Typically smaller than other galaxies.Generally, have many bright, young stars and lots of gas and dust to form new stars.
Have a loose, disorganized appearance and contain no more than a few thousand stars.
A large, round, densely-packed grouping of old stars.
An enormously bright, but very distant galaxy with a giant black hole at its center.
eclipsing binary star
A binary star system in which one star periodically blocks the light from the other star,at regular intervals.
A huge group of single stars, star systems, star clusters, dust and gas bound together by gravity.
Groups of two or more stars-more than half of all stars
Big Bang Theory
The theory astronomers have developed to describe the formation of the universe.
The observation that the farther away a galaxy is the faster it is moving away.
How long ago was the universe formed?
Approximately 13.7 billion years ago
A mysterious force that appears to be causing the expansion of the universe to accelerate.
Matter that does not give off electromagnetic radiation, but is quite abundant in the universe (up to 90% of matter).
Milky Way galaxy
spiral galaxy.Our solar system is found on one of the outer arms.
A distant star that moves back an forth may indicate what?
That a planet or secondary star may exist near the star, even though we can't see it.
How did our solar system first begin to form?
Five billion years ago a huge cloud of dust and gas called the solar nebula collapsed.
cosmic background radiation
The electromagnetic radiation left over from the big bang.
diameter of the Milky Way galaxy
about 100,000 light years