Download The Sun as a Star

Some Information about the Sun
Warning! You should never look directly at the Sun! Only look at the Sun with
special telescopes and filters, or by projecting an image of the Sun on a screen.
 The Sun is a star—the nearest star! See Figure 1
 How big is the Sun? How much does it weigh?
o Size: ~100 times as big across as Earth! (1.4 million km across)
 About one million Earths could fit inside the Sun!
o Mass: ~330,000 times Earth (2x1030 kg)
o The Sun is an average star—some stars are bigger, some smaller
 What’s the Sun made of?
o Hot gas! ~75% Hydrogen, ~25% Helium + some heavier elements
 How does the Sun (and other stars) work?
o Nuclear fusion—2 Hydrogen atoms fuse together to make 1 Helium atom, and
energy is released (E=mc2)
o Like a big hydrogen bomb!
o The fusion happens at the center of the Sun
 How hot is the Sun?
o The surface of the Sun that we see is ~6000 degrees
o The center of the Sun is about 15 million degrees!
 How old is the Sun?
o ~5 billion years old, about halfway through its life
o The Earth is about 4.5 billion years old
 Why does the Sun not collapse under its own weight?
o Gravity wants to pull the gas towards the center, but pressure from the hot gas
wants to expand the Sun: these two forces balance. Imagine the Sun as a balloon.
o This is also true for other stars
 How do we study the Sun?
o Using telescopes on the Earth (e.g. Kitt Peak Solar Telescope), and telescopes in
space (e.g. SOHO)
o Scientists also use computers to study the Sun
 What can we see on the Sun?
o Sunspots: these are places on the Sun that are cooler (by ~1500 deg) than the rest of
the Sun, so they look darker (they’re still quite bright actually). See Figure 2
o Prominences and filaments: dense, cold gas held above the Sun’s surface by the
Sun’s magnetic field (you can think of the Sun like a big bar magnet). See Figure 3
o Flares: Violent explosions that release lots of energy and particles from the Sun.
See Figure 4.
 How does the Sun affect the Earth?
o It gives us heat and light—important for life.
o It’s gravity keeps us in orbit around the Sun
o Solar flares cause Northern Lights, can disrupt communications and power, and
knock out satellites. See Figure 5
Fig 1: The Sun
Figure 4:
Solar Prominence
Fig 2: Sunspots
Fig 3: Prominences
Figure 5:
Northern Lights
Some WWW Pages on the Sun
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Space Weather (what’s happening with the Sun; auroras; meteor showers, etc):
http://www.spaceweather.com/
Daily Pictures of the Sun: http://umbra.nascom.nasa.gov/images/latest.html
The Sun from Solarviews.com (tons of info, pictures, movies, etc):
http://www.solarviews.com/eng/sun.htm
The Sun from Nine Planets (also a great site): http://www.nineplanets.org/sol.html
The SOHO satellite (studying the Sun from space): http://sohowww.nascom.nasa.gov/
NASA Sun Questions & Answers: http://helios.gsfc.nasa.gov/qa_sun.html
Curious About the Sun: http://curious.astro.cornell.edu/sun.php