1. Stars, Galaxies, and Constellations
Stars = objects in space, made of gases, which produce their own light and heat.
Earth’s nearest star is the sun (149,600,000 km away)
The next nearest star is Proxima Centauri (4.24 light years away)
Light year = the distance light travels in 1 year
Light travels at 300,000 km/s, or about trillion km in one year.

2. Measurement in Space
Parallax - the apparent shift in the position of an object when viewed from two different positions

3. Nuclear Fusion = reactions occur when hydrogen atoms combine to form helium atoms. *this produces great amounts of light and heat*
Different stars produce different amounts of energy.
The amount of energy produced by a star determines the star’s color and surface temperature.
Stars differ in composition, age, and size. *young stars are rich in hydrogen *older stars use up hydrogen to produce more helium

4. Classifying stars
Based on brightness and temperature
Hertzsprung-Russell Diagram

5. Evolution of Stars
Nebula - Stars begin as a large cloud of gas and dust
Main sequence – pressure from heat is in balance with gravity
Giant – outer layers of the star expand and cool
Supernova – star explodes
White dwarf – outer layer contracts (about size of Earth)
Neutron star – only neutrons can exist in the dense core
Black hole – gravity is so strong that nothing can escape, not even light

6. Apparent magnitude – how bright the star appears from Earth.
Absolute magnitude – how bright the star really is (if all stars were the same distance from Earth)

7. Galaxy = system of stars, dust, and gas held together by gravity.
Three major classes of galaxies:
Spiral Galaxy (Milky Way Galaxy) -disk-shaped with arms
Elliptical Galaxy -shaped like a football
Irregular Galaxy -no distinct shape

8. Constellations – groups of stars that form pictures in the night sky.
Orion

9. Astronomers recognize 88 constellations.
View of the north sky