Universe

Life Cycle of Stars 

1. Nebulae ➡️ protostar ➡️ main sequence star ➡️ red giant or supergiant ➡️ red giant or supergiant

➡️ white dwarf, neutron star, or black hole

2. The stars mass determines what route it takes.

3. Stars are born in cold clouds of dust and gas (nebulae) 

4. Sun's Life Cycle: Nebulae ➡️ Protostar ➡️ Main Sequence Star ➡️ Red Giant ➡️ Planetary Nebula ➡️ White Dwarf

HR Diagram 

1. The purpose of the H-R Diagram is to classify stars. The two variables found on the X and Y-axis are surface temperature and luminosity.

2. There are four groups of stars found on the H-R Diagram, they are Main Sequence, Giants, Supergiants, and White Dwarfs. Our Sun belongs to the Main Sequence group.

3. The relationship between temperature and brightness for the Main Sequence stars is the hotter the star the brighter it is. The X-axis is unique because it is inverted.

4. Top left corner - Hot & Bright, Top right corner - Cool & Bright, Bottom left - Cool & Dim, Bottom right - Hot & Dim

Galaxies 

1.  A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity (according to NASA Space Place).

2. Galaxies are classified by their shape and structure using the Hubble sequence. The 3 main types are spiral, elliptical, and irregular. 

3. Spiral - Disk shaped, with arms, full of dust and gas, and active star formation. Elliptical - Spherical in shape, contains older stars, with little dust or gas. Irregular: Chaotic, no definite shape, has a lot of gas and new stars.