Properties of the Stars

Distance

Stellar distances are measured in:

• Light Years - Distance light travels in one year (about 6 trillion miles or 9.5 trillion km).
• Parsecs - Distance at which 1 AU subtends 1 arcsecond (3.26 light years).

Distances to nearby stars are measured via parallax - the apparent shift in position as Earth orbits the Sun.

Magnitude

• Apparent Magnitude - How bright a star appears from Earth. Lower numbers are brighter (e.g., Sirius = -1.44, naked eye limit ≈ +6).
• Absolute Magnitude - How bright a star would appear at 10 parsecs. Allows comparison of intrinsic brightness.

Color and Temperature

Star color indicates surface temperature:

• O, B - Blue-white, hottest (30,000+ K)
• A - White (10,000 K)
• F, G - Yellow-white to yellow (6,000-7,500 K); Sun is G2
• K - Orange (4,000-5,000 K)
• M - Red, coolest (3,000 K)

The H-R Diagram

The Hertzsprung-Russell diagram plots stellar luminosity vs. temperature. Most stars fall along the Main Sequence. Giants and supergiants are above; white dwarfs are below.