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Chapter 30.1: Characteristics of Stars Star: ball of gas that gives off a tremendous amount of energy in the form of heat and light. Our own ‘Sun’ is considered an average star! Characteristics: 1. 2. 3. 4. 5. 6. 7. Starlight- light given off by stars. Composition- what elements make up the stars. Temperature- how hot; how cold? Size & Mass- how big; how small? Motion- actual motion vs. apparent. Distance- how close; how far away? Brightness- apparent vs. absolute magnitude. Starlight: -by analyzing the light stars emit, we can determine the star’s composition (elements present) and temperature. Composition: -Star composition is determined by analyzing the light being emitted. Equipment is called a spectrometer. -Since different elements absorb different wavelengths of light, elements can be determined. -Stars are made up of gas elements. (Hydrogen is the most common!) Temperature: -temperature is determined by the star’s color. -temp.’s range from 2,800 to 50,000 oC. Size & Mass: -Some dwarf stars are as small as the Earth. -Our sun is a medium size star (1,390,000 km). -Some stars are 1,000 times larger than our sun. -Density affects mass…no relationship between size and mass. Example: a star can be smaller than our sun, but have a greater mass…meaning it is more dense! Motion: 1. Actual motion- what we see with telescopes. 2. Apparent motion- This is motion visible to the unaided eye in a dark sky; due to movement of Earth. Stars have three actual motions: 1. rotate 2. revolve 3. move toward (blue shift) or away (red shift) from Earth Distance: -Light Year = 9.5x1012km; Distance that light travels in one year. Example: light from the sun takes 8 mins. to reach the Earth -Astronomical Unit (AU) - A unit of length used to measure distances in solar system. Example: Sun to Earth = 1 A.U. Brightness: a.ka. Stellar Magnitude -Absolute Magnitude: true brightness -Apparent Magnitude: brightness of a star as it appears to us on Earth. Brightest stars have lowest numbers. (negative #’s) Dimmest stars have highest numbers. (positive #’s)