Characteristics of StarsConstellations – imaginary patterns of starsCircumpolar – five constellations in the Northern Hemisphere that circle the pole star (Polaris)

Classification of StarsStars are classified by their color, temperature, size, brightness, and composition

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

Composition is determined by a spectrograph – a device that breaks light into colors and produces an image of the resulting spectrum

Measuring DistanceAstronomers 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

• 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