Transcript Characteristics of Stars PPT

Classifying Stars
•
•
•
•
•
Color
Temperature
Size
Composition/Mass
Brightness
Size Comparison
Size
Classification
Approximate
Size (km)
Examples
Neutron Star
16 km
Less than the
distance to
school
pulsar
White Dwarf
Less than the
distance across
Asia
Sirius B
Van Maanen’s
star
Medium star
109 X size of
Earth or
1,392,000 km
Sun
Giant star
100 X size of
Sun
Aldebaran
Supergiant
1000 X size of
Sun
Rigel, Betelgeuse,
Arcturus
Color and Temperature
Star Color
Surface Temp (oC)
Blue or Blue-White
35,000 oC
White
10,000 oC
Yellow
6,000 oC
Red-Orange
5,000 oC
Red
3,000 oC
Chemical Composition
• Most stars are made of
–
–
–
•
73% Hydrogen
25% Helium
2% Other elements
Astronomers use spectrographs to determine
elements found in stars
• Spectrograph is a device that breaks light into
colors and produces an image of the resulting
spectrum
Brightness of Stars
• The brightness of a star depends upon both its size
and temperature
• How bright a star looks from Earth depends on
both its distance from Earth and how bright the
star truly is
Brightness of Stars
• Apparent magnitude- The brightness of a star as it appears on Earth
• Absolute magnitude- The amount of light a star actually gives off
(uses formulas)
Why do stars twinkle?
• The scientific name for the twinkling of
stars is stellar scintillation
• Stars twinkle when we see them from the
Earth's surface because we are viewing
them through thick layers of turbulent
(moving) air in the Earth's atmosphere.
Measuring Distances to Stars
• Astronomers use a unit called the light year
to measure distances between the stars
• Light travels at a speed of 300,000 km/s
• Light year- distance that light travels in
one year =9.5 trillion km
• Light year=unit of distance
Parallax
• Astronomers use parallax to measure
distances to nearby stars
• Parallax= the apparent change in
position of an object when viewed from
two locations
Parallax is larger for closer objects