CHAPTER 21Characteristics of Stars

21.2

Distances to stars

Parallax is the method used by astronomers to study the distance to relatively nearby stars.

Parallax is the apparent change in position of an object when it is observed from a different place

Classifying Stars

The 3 Characteristics used to classify stars are Size, Temperature, & Brightness.

Sizes of Stars

The Sun is a medium size very ordinary star

Giant Stars are stars much bigger than our star the Sun A star like Betelgeuse would reach as

far as the orbit of Jupiter if it was where our Sun is.

Dwarf Stars are stars that are much smaller than our star Dwarf Stars are only about 20

kilometers in diameter.

Color & Temperature of Stars

A stars color tells you its temperature, their color indicates the size of the wavelength. The spectrum is used to indicate

temperature Red/Orange stars have the longest

wavelengths, thus they have the lowest temperatures

Blue/White stars have the shortest wavelength and have the highest temperatures

Brightness

How bright a star looks from Earth depends on how close it is and how much light it is actually giving off

Brightness

Apparent Magnitude is how bright a star is as seen from Earth Star’s brightness is compared to all the other

stars you see in the sky. Sirius is the brightest star in our night sky

Absolute Magnitude is how bright the star would be if it were as far away as our sun. To find the absolute magnitude an astronomer

must first find the apparent magnitude of the star and then find its distance.

H-R Diagram

It classifies stars according to absolute magnitude (brightness) and temperature (color). A diagonal band called the main sequence is

where 90% of all stars fall. Giant stars are to the upper right, and dwarf

stars are to the lower left.

H-R Diagram