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Chapter 21
Section 2
Page 752
Discover Activity-Parallax
Notes
Classifying Stars
Stars are classified by:
 Color and Temperature
What color stars are the hottest? _____________ Coolest? ______________
 Size
The sun is a medium-sized star. Stars that are much larger than the sun are called ______________
or __________________.
 Composition – The chemical composition of most stars is about 73 % ______________ and 25 %
____________________.
How can astronomers infer which elements are found in stars? ____________________________
_______________________________________________________________________________
 Brightness- This depends on both its _________________ and ___________________.
Apparent Brightness- a star’s brightness as seen from Earth.
( How bright it ___________ to be)
Absolute Brightness-a star’s brightness if it were a standard distance from Earth.
(How bright it _____________is.)
Measuring Distances of Stars
Astronomers use a unit called a ___________________ to measure distances between the stars.
A light –year is the distance that light travels in one _____________.
Astronomers often use ___________________ to measure distance to nearby stars.
Parallax is the apparent change in position of an object when you look at it from different places.
To measure parallax shift, astronomers look at the same star at two different times of year, when Earth is
on different sides of the _______________.
The Hertzsprung-Russell Diagram
Look on page 758 at Figure 10. Write what is measured on each of the two axes of the diagram.
a. x-axis (horizontal axis) _______________________
b. y-axis (vertical axis ) ________________________
An area on the H-R diagram that runs from the upper left to the lower right and includes more than 90
percent of all stars is called the ______________________.