1. Stars

2. What is a star?
The objects that heat and light the planets in a system
A star is a ball of plasma held together by its own gravity
Nuclear reactions occur in stars (H  He)
Energy from the nuclear reactions is released as electromagnetic radiation

10. Characteristics of Stars
Magnitude (brightness)
A measure of brightness of celestial objects
Smaller values represent brighter objects than larger values
Apparent magnitude
How bright a star appears to be from Earth
Absolute magnitude (luminosity)
How bright a star actually is

11. Temperature & Color
The color of a star indicates the Temperature of the star
Stars are classified by Temperature
Decreasing T (bright to dim)
O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ]

12. Classification of Stars
Temperature
Color O
20, ,000 K
Blue B
10,000 – 30,000 K
Blue-white A
7,500 – 10,000 K
White F
6,000 – 7,500 K
Yellow-white G
5,000 – 6,000 K
Yellow K
3,500 – 5,000 K
Orange M
2,000 – 3,500 K
Red

21. Life Cycle of Stars Life span of a star depends on its size.
Very large, massive stars burn their fuel much faster than smaller stars
Their main sequence may last only a few hundred thousand years
Smaller stars will live on for billions of years because they burn their fuel much more slowly
Eventually, the star's fuel will begin to run out.

22. One light-year is equal to 6,000,000,000,000 miles
Closest Star
Proxima Centauri
One light-year is equal to 6,000,000,000,000 miles
(9,500,000,000,000 kilometers.

23. What Do We Know
About The Universe
Hubble Telescope

24. Nearest Galaxy