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Transcript
24-2 Characteristics of Stars • Galaxy – a giant cluster of stars, gas, and dust held together by gravity – Milky Way Galaxy, Andromeda Galaxy • Universe – all of space and everything in it. Contains billions of galaxies. Distance to Stars • Astronomical Unit (AU) – average distance from earth to sun (150 million km) • Light year – distance that light travels in one year (9.5 million million km) Measuring Distances to Stars • Use parallax to measure distances from earth to stars – Parallax – apparent change in position of an object when you look at it from different places – Look at star when earth is on one side of the sun and look at same when earth is on other side of the sun – Measure how much the star has appeared to move – The less the star appears to move, the farther away it is Classifying Stars • Classify stars according to size, temperature and brightness – Stars give off own light due to nuclear fussion – Moon/planets reflect light from stars (sun) Size of Stars • • • • • Supergiant star Giant star Medium-sized star (our sun) White dwarf star Neutron star Color and Temperature of Stars • Coolest stars = red • Hot stars = white • Hottest stars = bluewhite Brightness of Stars • Brightness = amount of light given off • Depends upon size and temperature • How bright a star looks from earth depends upon how far away it is and how bright it is Apparent Magnitude • Is a star’s brightness as seen from earth – Depends upon distance Absolute Magnitude • Brightness star would have if it were at a standard distance from earth – True measure of brightness Hertzsprung-Russell Diagram • H-R diagram plots brightness vs temperature and shows the relationship between these two characteristics – Main sequence – 90% of all stars; brightness increases as temperature increases (our sun) – Giants and supergiants are at the top and right – White dwarfs are at bottom center
