Download 24-2 Characteristics of Stars

24-2 Characteristics of Stars
• Galaxy – a giant
cluster of stars, gas,
and dust held
together by gravity
– Milky Way Galaxy,
Andromeda Galaxy
• Universe – all of
space and
everything in it.
Contains billions of
galaxies.
Distance to Stars
• Astronomical Unit (AU) –
average distance from earth
to sun (150 million km)
• Light year – distance that
light travels in one year (9.5
million million km)
Measuring Distances to Stars
• Use parallax to measure distances from earth to
stars
– Parallax – apparent change in position of an object
when you look at it from different places
– Look at star when earth is on one side of the sun and
look at same when earth is on other side of the sun
– Measure how much the star has appeared to move
– The less the star appears to move, the farther away
it is
Classifying Stars
• Classify stars according
to size, temperature and
brightness
– Stars give off own light
due to nuclear fussion
– Moon/planets reflect light
from stars (sun)
Size of Stars
•
•
•
•
•
Supergiant star
Giant star
Medium-sized star (our sun)
White dwarf star
Neutron star
Color and Temperature of Stars
• Coolest stars = red
• Hot stars = white
• Hottest stars = bluewhite
Brightness of Stars
• Brightness = amount of
light given off
• Depends upon size and
temperature
• How bright a star looks
from earth depends
upon how far away it is
and how bright it is
Apparent Magnitude
• Is a star’s brightness as seen from earth
– Depends upon distance
Absolute Magnitude
• Brightness star would have if it were at
a standard distance from earth
– True measure of brightness
Hertzsprung-Russell Diagram
• H-R diagram plots brightness vs
temperature and shows the relationship
between these two characteristics
– Main sequence – 90% of all stars;
brightness increases as temperature
increases (our sun)
– Giants and supergiants are at the top and
right
– White dwarfs are at bottom center