1. Stars

2. A Star is….
A ball of matter that is pulled together by gravity, and that gives off energy as a result of NUCLEAR FUSION.
Nuclear fusion- when two atoms bond together to make one heavier atom. The process releases large amounts of energy.

3. 1. Composition of Stars
The two most abundant elements in stars are HYDROGEN and HELIUM.
Scientists determine the composition by studying the LIGHT that comes from a star.

4. How Light shows composition
When elements in a star burn, they give off certain colors of light. The color of light corresponds to a specific wavelength of the light.

5. How Light Shows Composition
Scientists look at the light from a star through a SPECTROSCOPE. A spectroscope breaks light apart and shows the wavelengths of the light.
Example: Color Spectrum of calcium:
The bright lines on the spectrum tell you the wavelength of the light given off.

6. How Light Shows Composition
Each element gives off a unique pattern, or color spectrum. If scientists find that pattern in a stars light, then they know that element is present in the star.
Example: When you burn sodium, it produces a yellow flame.
If a star’s spectrum has two lines in the same place, that star contains sodium.

8. How Light Shows Composition
Astronomers match up the lines on the spectrum coming from a star with the dark lines different elements produce when they burn to determine the composition of the star.

9. 2. Temperature
Scientists estimate the temperature of stars by the COLOR of the star.
Hottest:
Coldest:
Blue
White
Yellow
Orange
Red

10. 3. Magnitude Size Temperature Distance from us
The Brightness of a star depends on three things:
Size
Temperature
Distance from us
Apparent Magnitude: How bright a star is when viewed from Earth. A very large, hot star could look dim just because it is so far away. (how bright we see it)
Absolute Magnitude: the amount of light that is actually given off by a star. (how bright it actually is)

11. 4. Measuring Distance in Space
Light-Year- The DISTANCE that light can travel in one year. 5,865,696,000,000 miles
Astronomical Unit (AU)- the distance between the sun and the earth (93 million miles)

12. 5. Constellations Constellations are patterns of stars in the sky.
Circumpolar Constellations: Constellations that appear to revolve around the North Star.
Major constellations:
Orion
Big Dipper

14. 6. Important Stars
Polaris: The North Star: The star directly above the earth’s axis of rotation, or the north pole. It appears to stay in the same place all year, and other constellations revolve around it.
Alpha Centauri: Closest star to us (other than the sun)