Ch 26.2 Properties of Stars

1. Color & Temperature

Blue = Hottest (30 000 K surface temp.)

Yellow = (5000 – 6000 K; sun like)

Red = Coolest (3000 K)

Properties of Stars

2. Star Brightness (Magnitude)

Why might one star appear brighter than another?

1.Closer

2.Bigger

3.Hotter

Properties of Stars2. Brightness or Magnitude Ratings

Magnitude = Brightness rating

1st 2nd 3rd 4th 5th 6th

Brightest Dim(Negative #s are VERY BRIGHT)

Apparent Brightness (Magnitude)

The brightness of a star as it appears from Earth (Decreases w/ distance)

Sun (-26.72), Betelgeuse (-0.50)

Absolute Brightness (Magnitude)How bright the star REALLY is.Sun (4.8), Betelgeuse (-7)

Properties of Stars 3. Size & MassOnce astronomers know a star’s temp &

absolute brightness, they can estimate its diameter & calculate volume.

Properties of Stars4. Composition

Stars vary in their chemical compositon.

Young stars start off as mostly hydrogen.

As stars age, they consume lighter elements like hydrogen and increase their abundance of heavier and heavier elements.

Spectroscopes are used to determine a star’s composition.