Stars
How bright a star is depends on the temperature and size of the star. Absolute brightness of stars are measured by how bright a star is if it was 10 parasecs away whereas apparent brightness is how bright the star looks from the earth. For apparent brightness, the farther the star is the less bright it will be. Apparent brightness depends on how bright the star is, the size of the star, and how far the star is from the earth. However, absolute brightness lets us know the actual brightness of the star. The luminosity of the star can also depend on it's size. Most likely, larger stars are more luminous.
Star's Temperature
Star colors can range from red, blue, white, and gold. Stars that appear red are cool stars. In the electromagnetic spectrum, cool stars radiate energy mostly in the infrared and red regions. Meanwhile, stars that radiate most of their energy at the blue and ultraviolet regions of the electromagnetic spectrum are called hot stars. These stars look white or blue. To determine the temperature of a star, the blackbody temperature and where the spectrum peaks for the wavelength of light is needed.
Hertzsprung–Russell Diagram
Diagram of stars on a scatter graph displaying how the absolute brightness relates with the spectral classifications and temperatures. This diagram can classify a star as main sequence, white dwarf or red giant on the basis of its brightness and color.
Main Sequence Stars
Main sequence stars are also known as dwarf stars. These stars contain hydrogen in or near their cores that turn into helium. The helium increases at a steady pace. This is from high temperatures and pressure reactions. These stars can increase in temperature and luminosity and can lose solar mass.
History and Future of the Universe
Below is a great source to learn about the history and the future of the universe (better than I can explain)! It has videos and pictures to help explain.
http://www.space.com/13352-universe-history-future-cosmos-special-report.html
http://www.space.com/13352-universe-history-future-cosmos-special-report.html