Transcript Characteristics of Stars

Characteristics of Stars
19.1
Basics
• Star = body of gas
• Gives off heat & light
• Vary in size, color, composition,
temperature & brightness
Composition & Texture
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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