Ch 26-2

Characteristics of Stars

5 Common Characteristics of Stars

• 1. Size

• 2. Mass

• 3. Color

• 4. Temperature• 5. Brightness

Size of a Star• Stars are divided into 5 main Groups by size

1. Neutron Star• **Can be the distance you travel to

school 2. White Dwarf Star

• **Can be the size of Asia• 3. Medium-sized Star

• **Our own Sun

Size of a Star• 4. Giant Star

• *The diameter 10 to 100X larger than our sun

• 5. Super-giant Star• *The diameter 1000X larger than sun

• ** If our sun were replaced with a SGS the star would extend beyond

Mars and Earth would be burned up• **Die quickly—Short lived stars

Composition • Astronomers use a spectroscope to

determine what stars are made of by their spectral lines

•  All stars have the similar composition• Most common element = Hydrogen 60-

80% of total mass of a star

• 2nd most common element = Helium • Trace elements = O, Ne, C, N -- 4%

of total mass of a star

Surface temperature • Star color indicates surface

• temperature 3,000* k = Red star = Cool

• Sun= 6,000*k = Yellow star = Hotter

•  

• 50,000*k = Blue-white light = Hottest

Brightness

• Brightness of a star depends on 3 things

•  

• 1. Size of a star

• 2. Surface temperature

• 3. Distance from Earth

Apparent Magnitude • The brightness of a star as observed from

Earth 

• Absolute Magnitude• Put two stars at equal distance from each

other you can see which is brighter• Can’t move stars so must calculate

brightness• A CALCULATION OF ACTUAL

BRIGHTNESS• Brightness for most stars is constant

Hertzsprung- Russell Diagram

• Shows the relationship between Absolute magnitude and surface temperature