Characteristics of Stars

19.1

Basics

• Star = body of gas• Gives off heat & light• Vary in size, color, composition,

temperature & brightness

Composition & Texture

• Spectrometer: separates light into colors• Each element has unique spectra• Most stars are made of H, He, Fe, Na, Ca• Color indicates surface temp of star:

– Blue = hotter (30,000 C)– Red = cooler (3,500 C)

Motion

• Apparent motion id due to earth’s movement

• Circumpolar stars appear to move around the north star (Polaris)

Distances

• Light travels ~ 10 trillion km/yr• Proxima centauri is the nearest star at 4.3

l.y. away • Sirius is brightest star at 9 l.y. away • Polaris is 700 l.y. away• Andromeda Galaxy is 2.5 million l.y. away• Parallax

Magnitudes

• 6000 stars are observable to unaided eye• 3 billion stars can be seen with ground

based telescopes

Apparent magnitude

• Brightness of a star as it appears from earth

• Brightest stars have lowest #s• Dimmest stars have highest #s

Absolute magnitude

• True brightness as stars would appear if seen from 32.5 l.y. from earth

Classification

• H-R diagram• Absolute magnitude vs. temperature• For most stars the brightness increases as

surface temp increases• Main sequence stars are band in center