1. The Big Bang Thoery

2. The Big Bang theory is a commonly accepted theory of how the Universe began.
According to the Big Bang theory, our Universe burst into sudden existence in a massive explosion called the Big Bang and it's still evolving.

3. The Big Bang probably occurred around 13
The Big Bang probably occurred around 13.7 billion years ago if the theory is valid.

4. Matter and radiation from the fireball expanded and cooled
Matter and radiation from the fireball expanded and cooled. within seconds, protons, neutrons and formed. Minutes later, hydrogen, and other trace elements were created.

5. Millions and millions of years later, as matter and radiation separated, galaxies and stars started to form.

6. Galaxy: Galaxies are sprawling space systems composed of dust, gas, and countless stars. The number of galaxies cannot be counted—the observable universe alone may contain 100 billion. (use your chart now to take notes)

7. Some of these distant systems are similar to our own Milky Way galaxy, while others are quite different.
Galaxies with less than a billion stars are considered "small galaxies." In our own galaxy, the sun is just one of about 100 billion stars.
Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies.

8. Spiral:
-Their long twisting arms are areas where stars are being formed.
-Some of the new stars
created in the wave are very
large. Because of their size
these large stars glow brighter
than their smaller cousins,
causing the nearby dust
clouds to glow brightly.
Older stars reside in the bulge at the center of the galactic disk

9. Examples:
The Andromeda Galaxy (M31)
Triangulum
Whirlpool

12. 2. Elliptical: The stars found in Elliptical Galaxies are often very old. This is because elliptical galaxies don't actively create new stars. The only stars found with in them were created along time ago. The stars in an elliptical galaxy are often very close together making the center look like one giant star. If the Earth were inside an elliptical galaxy it would be bright both day and night.

13. Examples:
M87 (or Virgo A)
Maffei 1 (the closest giant elliptical galaxy)

14. 3. Irregular Galaxies All the galaxies which are not spiral or elliptical. They can look like anything and have many different characteristics.

15. Local Group