Chapter 21, Section 2 Characteristics of Stars. Distance to Stars Light-year- The distance that...
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Transcript of Chapter 21, Section 2 Characteristics of Stars. Distance to Stars Light-year- The distance that...
Distance to Stars• Light-year- The distance that light travels in one
year, it is about 9.5 trillion kilometers ( that is 9.5 million million kilometers)
• Measuring distances with ParallaxParallax is the apparent change in position of an object when you look at it from different placesUsed only for nearby stars by looking at how stars move as the Earth goes around the sun.
Classifying Stars
• The main characteristics used to classify stars are
–Size
–Temperature
–Brightness
Sizes of Stars• Many stars are about the size of the sun
the sun is medium-sized• Very large stars are giant stars or
supergiant stars-The Supergiant Betelgeuse would
extend out to Jupiter if it was in sun’s position
• White dwarfs are Earth-sized• Neutron stars are only 20km in diameter
Color and Temperature of Stars
• A star’s color reveals its temperature
Cool stars burn RED at @ 3200°C
Hottest stars are bluer than white
and are blue-white burning at 10,000°C
Brightness of Stars• Brightness depends on size and
temperature• Apparent magnitude- is brightness as
seen from Earth
• Absolute magnitude- is brightness the star would have if at a standard distance from Earth
Hertzsprung-Russell Diagram
• H-R Diagram is a graph relating the temperature and brightness of stars
-Brightness increases moving up y-axis- Temperature decreases moving right on
x-axis• More than 90% of all stars are in a diagonal
band called the Main sequence- In the main sequence, temperature
increases as brightness increases- The sun is in the main sequence
Hertzsprung-Russell Diagram
• Upper right side of H-R diagram contains giant and supergiant stars
• White dwarfs are hot but not bright so the are at the bottom center of the H-R diagram
Hertzsprung-Russell Diagram
Image from http://austrinus.com/02/imagenes/diagrama_hr_2.jpg