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Stars Chapter 2 Section 1 What does the color of a star tell you? The color of a star will tell you it’s temperature Colors such as red and yellow = cooler temperature stars Blue and white stars = hotter temperature stars All stars are different, but how are they classified? Stars are classified by brightness and temperature. Stars are classified in order of highest to lowest temperatures.(OBAFGKM) hottest stars being classified as O coolest stars being classified as M. Star’s are also classified according to their brightness. Luminosity is the amount of energy emitted by a star each second How do we tell what stars are made of? Each star is made up of specific gases. Astronomers can tell what elements a star is made up of by observing the light given off. The inner layers of a star are very dense and hot. The outer layers are made up of cool gases. How do they observe the light? Astronomers use a tool called a spectrograph, which breaks down light into its different wavelengths. The different wavelengths create what is called a spectrum. How do different elements look? If you look at gases such as: nitrogen, oxygen, hydrogen…. through a spectrograph it will create emission lines. Gases only give off certain colors of light or certain wavelengths, these are emission lines. Why don’t stars give off bright line emissions? The cool atmosphere of a star absorbs certain colors of light or wavelengths. This creates dark line emissions. These types of spectrums are known as absorption spectrums. They help scientists to identify the elements that make up a star’s atmosphere Spectroscope Lab Fluorescent light krypton Sunlight Neon Helium Nitrogen How do we determine the brightness of a star? The brightness of stars from earth is known as its apparent magnitude. This depends on size and energy output This is not it’s true brightness In order to find a star’s absolute magnitude (how bright it actually is) astronomers use the star’s apparent magnitude and it’s distance from earth. Distances and Motion of Stars. Distance can be measured in either light years or Kilometers. In order to determine this number astronomers use a star’s parallax and simple trigonometry. Parallax is the apparent shift of a star’s position when viewed at different locations. The North star is 431 light years away Motion of Stars Star’s seem to move at night due to the rotation of earth on it’s axis. Know as a stars Apparent Motion Because of this all the stars appear to rotate around Polaris (North Star) Star Trails Orion star trails Big Dipper star trails Orion star trails North Pole star trails Apparent motion But stars actually do move in space, this can be seen by the movement of stars over a time period of thousands of years. This is called Actual Motion Actual Motion Focus Questions How is color related to star temperature? What produces an absorption spectrum? Explain two ways in which stars are classified. What the difference between apparent magnitude and absolute magnitude? Why do stars seem to revolve around Polaris? Doppler effect- as a car approaches it sounds higher in frequency (pitch). The same thing occurs with light. Moving Away - redshift Moving Towards - blueshift Doppler Effect