Characteristics of Stars p. 775 - 780 Chapter 30 Characteristics of Stars p. 775 - 780

What is a star? Body of gas that gives off light and heat vary in: color size temp, composition distance brightness

Analyzing Starlight spectrometers separate light spectra can tell the composition and temperature of a star

Star Composition Mostly hydrogen and helium

Star Temperature Blue – Hot Yellow - Medium Red - Cool

Apparent Motion of Stars Looks like all stars are moving westward around the North Star Due to earth movement Circumpolar Stars – circle North star , never go below horizon

Actual Motion of Stars Rotate on Axis May revolve around another star

3. Revolve around center of galaxy

4. Some Move toward earth (blue shifted) Some move away from earth (red-shifted)

Distance to Stars about 9.5 trillion km/year 300,000 km/s Measured in LIGHT- YEARS or the distance that light travels in one year

Distance to Close Stars (within 1000 light years) Measured with PARALLAX -shift in the apparent position of the star when viewed from different angles

Stellar Brightness Apparent Magnitude - brightness as it appears from earth - more negative = brighter

2. Absolute Magnitude – brightness if all stars were the same distance from Earth.