Classifying Stars Color Temperature Size Composition/Mass Brightness

Less than the distance to school Size Comparison Size Classification Approximate Size (km) Examples Neutron Star 16 km Less than the distance to school pulsar White Dwarf Less than the distance across Asia Sirius B Van Maanen’s star Medium star 109 X size of Earth or 1,392,000 km Sun Giant star 100 X size of Sun Aldebaran Supergiant 1000 X size of Sun Rigel, Betelgeuse, Arcturus

Color and Temperature Star Color Surface Temp (oC) Blue or Blue-White Yellow 6,000 oC Red-Orange 5,000 oC Red 3,000 oC

Chemical Composition Most stars are made of 73% Hydrogen 25% Helium 2% Other elements Astronomers use spectrographs to determine elements found in stars Spectrograph is a device that breaks light into colors and produces an image of the resulting spectrum

Brightness of Stars The brightness of a star depends upon both its size and temperature How bright a star looks from Earth depends on both its distance from Earth and how bright the star truly is

Brightness of Stars Apparent magnitude- The brightness of a star as it appears on Earth Absolute magnitude- The amount of light a star actually gives off (uses formulas)

Why do stars twinkle? The scientific name for the twinkling of stars is stellar scintillation Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.

Measuring Distances to Stars Astronomers use a unit called the light year to measure distances between the stars Light travels at a speed of 300,000 km/s Light year- distance that light travels in one year =9.5 trillion km Light year=unit of distance

Parallax Astronomers use parallax to measure distances to nearby stars Parallax= the apparent change in position of an object when viewed from two locations

Parallax is larger for closer objects