2. Stars
• What is a star ?
• Stars are made up of …………………..
• Stars vary in size, color, temperature and
brightness.
• Stars can be bound together by gravity to form
multiple star system.
3. Characteristics of stars
1. Size
The Solar radius (radius of the sun 695,000km)
is used to describe the size of other stars.
White dwarf 0.01 solar radius
Giant stars 10-100 solar radius
Super giant up to 1000 solar radius
4. 2. Brightness & luminosity
Apparent magnitude is a measure of star’s
brightness as seen from Earth
Ancient astronomers, using only their eyes,
described star brightness by magnitude.
Absolute magnitude is a measure of how bright
a star would be if seen at a standard
distance. It measures luminosity
5. • Absolute magnitude is a measure of the
brightness of a star whose distance from Earth
is known.
• When astronomers use the word luminosity,
they mean the actual brightness of a star. They
measure it on a scale called absolute
magnitude.
6. 3. Color & Temperature
• Stars have different colors.
• The differences in the colors of stars are due
to differences in their surface temperatures.
• Stars that have the lowest surface
temperatures (below 3,500 °C) are red.
• Stars that have the highest surface
temperatures (above 25,000 °C) are blue.
7. Red orange yellow yellow-white white blue-white blue
Coolest Hottest
• Blackbody is an object that changes color
when temperature changes.
• As the temperature of a blackbody rises, it
glows brighter and brighter.
8. The Sun
• Composition : Hydrogen & Helium
• Size: 695,000 km
• Temp : 5,500 degrees
• Color: yellow
• Apparent magnitude: -26.8
• Absolute magnitude: +4.8
