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Transcript of The Sun
I. Energy from the Sun
Temperatures in the Sun's core are over 15 million K (@ 27 million F)
The extreme heat and density in the core causes less massive hydrogen nuclei to combine (fuse) into more massive Helium atoms. This is known as
. Nuclear fusion releases tremendous amounts of energy.
3.9 X 10 to the 36th power Watts.
4 trillion, trillion 100W light bulbs.
90 Billion H-Bombs / sec
II. Forces in Balance
The mass of the sun generates enough
into the core to balance the amount of pressure from
out from the core.
Astronomers estimate the sun will remain stable for another 5 billion years.
Physical Characteristics of the Sun
Diameter = @865,000 miles or
110 X that of Earth.
Mass = 1.3 million Earths.
(99.8% of the solar system)
, - fusion
- highly compressed gas
- convection currents
= visible surface. Temp = 10,000 F
= Middle layer. Temp = over 17,500 F
= thin outer layer. Temp= @1.8 million F
Corona extends millions of km into space and gradually thins into Solar Winds that carry electrically charged particles (Aurora)
Other Features of Sun's Atmosphere
= Appear as darker areas of cooler, more dense gas in photosphere
= Huge loops of gas that erupt from sunspot regions.
= Sudden release of energy from sun's surface hurling x-rays into space. These increase corona temperatures about 20 X, and greatly increase solar winds that cause magnetic storms in Earth's atmosphere.
Distances to Stars
= Distance light can travel in a year.
Speed of Light = 186,000 mi. / sec (around equator 7.5 X in a second)
Light year =
5.88 trillion miles
Alpha Centauri (visible) 4.4 light years @ 26 trillion miles.
Proxima Centauri (not visible) 4.3 light years
is the apparent change in position of an object with respect to background objects. Hold thumb out and close one eye, now switch eyes. The apparent movement is parallax.
Used to measure nearby stars. The closer the star, the greater the parallax angle
II. Characteristics used to classify stars
Color and Temperature
Blue= hottest, Yellow= medium, Red= Coolest
= how bright a star appears from earth. Apparent brightness decreases with distance and size
= how bright a star actually is. Calculated by distance from Earth and apparent brightness.
Size and Mass
Diameter is calculated from distance and brightness.
Mass of stars estimated by observing gravitational pull of stars on other stars.
Observing the dark absorption lines in a stars spectrum.
Most stars are composed of hydrogen and helium like our Sun
III. Life / death of a star
Main Sequence Stars
Most of a star's life cycle is spent in the
. This is when the forces of gravity and fusion are relatively
90% of stars are main sequence stars.
Our sun is about half way through its main sequence. (10 billion years)
Giants (low mass) and Supergiants (high mass)
As stars move out of the main sequence they become giants (small to medium stars - Sun is a medium star), or supergiants (largest stars 100-1000 x sun).
Remains of low mass stars at end of life cycle. Small, dense and hot, but dimmer than main sequence stars.