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What are stars?
Glencoe: Chapter 26-2 Outline
Astronomy
• The study of objects and matter outside
the Earth’s atmosphere and of their
physical and chemical properties.
I. What are stars?
A. Ancient peoples
(Greeks) thought
that all stars were
equal distance
from the Earth
- They grouped
stars into patterns
called constellations
What are stars?
 depicted characters in mythology
What are stars?
- We know now that the stars in a
constellation are not necessarily very
close together, but appear to be due to our
line of sight
- Examples – Orion, Ursa Major (Big Dipper)
B. Our sun
- Average in size
- Average in temperature
- Diameter is 110 times the size of the Earth
- Mass = 300,000 times that of Earth
- Slightly more dense than water
C. Star brightness
- Depends on the star’s temperature, size,
and distance from the Earth
D. We learn about stars by studying
their light
- Visible light
- Electromagnetic radiation at other wavelengths
 x-rays, radio waves, ultraviolet waves
- Today’s sophisticated telescopes can detect and
chart all these types of waves
E. Star color is related to star temperature
- Hotter stars emit more
intense light at the
shorter wavelengths
 more blue light
- Cooler stars emit more
intense light at the
longer wavelengths
 more red light
E. Star color is related to star temperature
- Color is determined by which color /
wavelength is emitted the most
*Our sun emits yellow light as its most
intense wavelengths
- From studying our sun’s light, we have
determined that the sun is 90%
hydrogen atoms
F. Stars are huge fusion reactors
- Hydrogen atoms are
fused to make helium
atoms and release
energy out
- Energy then moves
through the parts of a star
and out into space