1. Milky Way and other Galaxies

2. Galaxy- a collection of stars, dust, and gas
bound together by gravity
-Galaxy contain millions or billions of stars
-There are more than 100 billion galaxies
-Galaxy contain young stars( found near nebular gas) and older stars( in regions that contain no gas and dust)
-Gravity holds galaxies together in clusters
Cluster- a group of stars or galaxies bound by gravity

4. Edwin Hubble used the telescopes to explore galaxies beyond the Milky Way galaxy
The Hubble Space Telescope, now probes the depths of the universe from its orbit above Earth

5. Types of galaxies Spiral Galaxy (side view) Spiral Galaxy (top view)
Elliptical galaxy (end view)
Elliptical Galaxy (side or top view)

6. Interstellar matter- gas and dust between the stars
Edwin Hubble divided all galaxies into three major types: spiral; elliptical, and irregular
We live in Milky Way Galaxy, what is a spiral galaxy, the nucleus is very dense and has many old stars, the arms have both old and new stars
Interstellar matter- gas and dust between the stars
Irregular Galaxy

7. Elliptical galaxies have no spiral arms, they contain mostly older stars and have little interstellar matter
All other galaxies are irregular galaxies, they don’t have a well-defined structure
Milky Way Galaxy, can be seen as a faint, narrow band of light and dark patches across the sky, this band consist in stars, gas and dust in our galaxy

9. Quasar- quasi-stellar radio sources; very luminous objects that produce energy at a high rate, ant that are thought to be the most distant objects in the Universe
Each quasar has a huge center black hole and a large disk of gas and dust around it
They can be the central parts of distant galaxies

11. Origin of the Universe
Universe- the sum of all space, matter, and energy that exist, that have existed in the past, and that will exist in the future
Most of the Universe is empty space, space is a vacuum with no aer and no air pressure.
The Big-Bang theory states that the Universe began with a gigantic explosion 10 billion to 20 billion years ago, the explosion released all of the matter and energy that still exist today

12. Big-Bang theory- theory that all matter and energy in the universe was compressed into an extremely small volume that 10 to 20 billion years ago exploded and begun expanding in all directions
The future of the universe is uncertain: will keep expanding forever, or expansion of the universe will gradually slow down and the universe-will approach a limit size, or the universe will stop expanding and start to fall back in on itself

13. The fate of the Universe depends on mass:
-if is not enough mass, the universe will keep expanding forever
if there is the right amount of mass, the expansion will continually slow down but never stops
-if is more mass than this right amount, gravity will overcome the expansion and the universe will start to contract

14. New technologies helps scientist test theories, by making observations to see whether the theories make accurate predictions
Astronomers estimate the mass of the universe by measuring , stars, galaxies, and matter in the interstellar medium.
There is more matter than what is visible, is called dark matter, may be planets, black holes or brown dwarfs
90% of Universe may be composed of dark matter