Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Red Giant Star
Name: smarty
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1993 - 1999


Question:
I don't know how a red giant star comes along. Could you please mail the answer to mrabkin@eis.calstate.edu


Replies:
The "Red Giant" phase is part of the "lifetime" of average stars like the Sun -- kind of like a star's "late middle age". All stars begin as being made up almost entirely of hydrogen. A star begins its "life" by converting its hydrogen into helium. Because the heat and pressure of a "young" star is greatest at its center, the conversion of hydrogen to helium is fastest in the deep interior. Eventually, all of the hydrogen in the star's core is converted to helium and nuclear reactions stop there, while outside the core the reactions continue. At this stage, there is no heat being generated in the core; because of this, the core starts to contract. The contraction supplies energy to the core, which then gets hot- ter than ever. This heat is conveyed to the outer layers, which speeds up the hydrogen-to-helium reactions in the outer layers. This causes the outer layers to get hotter too, and to expand enormously. But the expansion causes the temperature of the outermost layers to drop, and they become "only" red-hot (just as white-hot metal cools to red-hot). This will happen to our Sun (several billion years from now); it will expand past Mercury's orbit, perhaps as far as Earth's orbit. Our oceans will boil away, and everything on Earth will be burned to a crisp.

I know of three easy-to-see red giants that are visible in the Northern Hemisphere: Antares in the constellation Scorpio, Betelgeuse in the constellation Orion, and Aldebaran in the constellation Taurus. If you can view them in a clear, dark sky away from city lights, you will see that they truly look reddish -- a sort of rusty red, like Mars.

RC Winther



Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory
n b