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Bell Ringer 9/29 • What are stars made of? 29.2 - Stars Star • A star is a body of gases that gives off a tremendous amount of radiant energy in the form of light and heat • Appear to be tiny specks of white light • Most vary in color and are much larger than Earth Motion • Stars move through the night sky towards the west • Stars rotate around the North Star, Polaris – Circumpolar = stars that circle around Polaris • Because of the earth’s rotation, some stars are not visible during particular seasons Constellations • Pattern of stars • Location changes throughout the year due to Earth’s orbit – Classified by season • 3000 years ago, people observed and recorded shifting patterns – Knew when to plant, harvest, and celebrate rituals based on location of constellations Constellations • Astronomers recognize 88 constellations • Constellations are named for animals, ancient gods, & legendary heroes – Most do not look like what they are named for Common Constellations • • • • • Ursa Major (Big Dipper) Ursa Minor (Little Dipper) Draco the Dragon Orion Zodiac Animals Constellation stars • Astronomers use constellations to locate particular stars • Stars within a constellation are named according to apparent magnitude – Brightest star is labeled alpha – Next brightest beta and so on • Some constellation stars have individual names – Polaris (North star) in the Little Dipper Constellation Project • Starting September 25, we will being a class project on Constellations • You will pair up and pick a constellation • Do some research on the constellation • Make a visual aid about the constellation Constellations to choose from • • • • • • Aquarius Aries Cancer Capricornus Gemini Leo • • • • • • • • • • • Libra Pisces Sagittarius Scorpius Taurus Virgo Ursa Major (Big Dipper) Ursa Minor (Little Dipper) Draco the Dragon Orion Cassiopeia • • • • • • Cygnus Hercules Pegasus Hydra Lyra Centaurus Star Clusters • Stars appear to be close to each other because the human eye cannot distinguish the distance a star is from earth • Clusters are stars close to each other due to gravitational attraction Binary Stars • Multiple-star systems – Pairs of stars that revolve around one another – Gravitationally bound & orbiting a common center of mass • Used to determine stellar mass • Appear as a single star to the human eye Distance • Astronomers use different methods to measure the distance between stars and Earth Distance to Stars • Distance to stars from Earth is measured in Light-years – Light-year = distance light travels in one year – Light-year = 9.461 x 1015 m Light • Light travels 9.5 trillion km in one year – Speed of light = 300,000 km/s – Sun is 8 light-minutes away because it takes 8 minutes for the sunlight to reach Earth • Parsec = 3.26 light-year = 3.086 x1016 m Parallax • Apparent shift in position caused by motion of observer • Change in position of Earth as it orbits – Closer stars have larger change in parallax – Farther stars have smaller change in parallax • Distance determined by angle of change Parallax Example of Parallax • Extend your arm and hold up your left thumb • Close your right eye and note location of thumb as compared to classroom wall • Now close left eye and note location of thumb Example of Parallax • You will see your thumb appears to move • This movement is because your eyes view everything at different angles, since they are a couple centimeters apart on your face • If you move your thumb closer to your face you will see a bigger change in thumb location In-Class Assignment/Homework • WKT 29.2 29.2 B Notes Properties of Stars • • • • Mass Diameter Luminosity (Magnitude) Temperature Magnitude • Apparent Magnitude = how bright a star appears • System established by Greeks • Brightest stars = +1 Magnitude • Absolute = how bright a star would appear at 10 parsecs (30 light-years away) • Allows for comparison based on how bright stars would appear at equal distances Magnitude • Luminosity = Energy output from surface of stars • Measured in watts – Think light bulbs Temperature • Stars are assigned spectral type then further subdivided into numbers – O stars have a temperature of ~50,000 K – M stars have a temperature of ~2000 K • Based on temperature and pattern of spectra lines – Sun = G2, temperature = ~5800 K • Temperature also related to luminosity and absolute magnitude Composition • • • • All stars have nearly identical compositions ~73% Hydrogen ~25% Helium 2% - other elements Classification of Stars • H-R diagram = graph showing pattern between absolute magnitude and surface temperature of a star – Charts absolute magnitude, temperature & spectral type • Brightness of stars increases as surface temperature increases H-R Diagram H-R Diagram • Main-sequence stars = band of stars running through middle of diagram – Sun and most stars in our sky are mainsequence stars • Band extends from cool, dim, red in the lower right corner to hot, bright, blue stars in upper left corner Main Sequence • Fusing Hydrogen in core • As stars evolve they begin to fuse Helium and burn hydrogen – High mass stars burn Hydrogen faster than low mass stars H-R Diagram • Other types of stars – Giants= very large, cool, bright star – Supergiants = extremely large, giant star – White Dwarfs = small, hot, dim star In-Class Assignment/Homework