Characteristics of Stars

1. Characteristics of Stars Constellations – imaginary patterns of stars Circumpolar – five constellations in the Northern Hemisphere that circle the pole star (Polaris) Classification of Stars • Stars are classified by their color, temperature, size, brightness, and composition

2. Composition is determined by a spectrograph – a device that breaks light into colors and produces an image of the resulting spectrum Brightness depends on size and temperature and there are two types • Apparent – brightness as seen from Earth • Absolute – brightness the star would have if it were at a standard distance from Earth Measuring Distance Astronomers use light years – the distance that light travels in one year, about 9.5 million million kilometers Astronomers use parallax – the apparent change in position of an object when you look at it from different places

3. Hertzsprung-Russell (HR) Diagram • graph used to determine a stars classification • it helps identify stars by color, size, temperature and brightness. • about 90% of stars fall on the main sequence. • the other 10% of stars were once main sequence stars. • can help determine where a star is in its lifecycle