Red Giants

A state of stellar evolution beyond the main-sequence life of a star. A red giant core is degenerate ionized helium, surrounded by a shell of hydrogen fusion, that expands the outer atmosphere in response to higher core temperatures. The hydrogen fusing shell eats through the surrounding atmosphere and deposits helium onto the shrinking core. The ballooning atmosphere cools and glows red; hence red giant. The Sun will become a red giant the size of Earth's orbit in five to six billion years. Once the helium core reaches 100 million degrees, it explosively begins fusing helium. The birth of the active helium core is called the helium flash. The Sun as a red giant will fuse helium for about 2 billion years after the helium flash.

Featured Images

Diagram comparing sizes of Sun, Aldebaran
Giant Eye Monday, July 21, 2014
RS Ophiuchi Monday, June 1, 2009
Dog Stars Saturday, January 31, 2009

Radio Programs

Moon and Aldebaran The beginning of the end Thursday, July 4, 2013
Crimson Star An aging but colorful star Sunday, February 3, 2013
The Footstool A footstool for the hunter Friday, December 28, 2012
Menkar A constellation with a case of the big head Sunday, November 18, 2012
Bear’s Nose The great bear’s shiny nose Sunday, May 27, 2012
Serpens Piecing together a celestial snake Saturday, May 12, 2012
Capella A quick exit for a “heavy” star Friday, April 27, 2012
Venus and Aldebaran The demise of a star and planet Sunday, April 8, 2012
Beta Pegasi Taking a look into the future Wednesday, November 30, 2011
Moon and Aldebaran Looking at the Sun’s bright future Sunday, September 18, 2011
Sagitta Arrowing into the autumn season Sunday, September 4, 2011
Moon and Aldebaran Predicting the future of a star Thursday, April 7, 2011
Early Summer Flip-flopping the seasons Tuesday, December 14, 2010
Vulpecula A dead star and an almost-dead star Saturday, August 7, 2010
Moon and Aldebaran A star that's changing in a hurry Thursday, July 8, 2010
Eltanin In search of the dragon's head Wednesday, June 23, 2010
Hercules A fairly weak "strongman" Monday, May 3, 2010
Little Dipper Anchoring a celestial dipper Sunday, April 4, 2010
Unicorn Stars Impressive stars for the unicorn Wednesday, February 24, 2010
Lynx Padding after a faint celestial cat Saturday, February 13, 2010
Tin Heavy metal the slow way Thursday, January 21, 2010
Keeping Watch Keeping watch on a distant star Thursday, August 20, 2009
Giants Giant stars in the evening sky Sunday, July 26, 2009
Venus, Mars, Aldebaran From one orange companion to another Monday, July 13, 2009
RS Ophiuchi One star gives, another takes Monday, June 1, 2009
Rasalhague A preview of coming attractions Sunday, May 31, 2009
Big Hand A big hand for a snake charmer Sunday, May 24, 2009
Arcturus Life around a giant star Saturday, May 23, 2009
Moon and Gemini The Moon and some puffy stars Thursday, April 2, 2009
Bear's Leg The bear's faint leg Saturday, February 28, 2009
Doomed Planet Sealing the fate of a giant planet Tuesday, February 24, 2009
Hind's Crimson Star A star with a ruddy complexion Sunday, February 15, 2009
Lepus Chasing away some pesky wabbits Saturday, February 14, 2009
Hydra Two steps in the future of the Sun Saturday, February 7, 2009
The Bull's Eye Staring into the eye of the bull Sunday, January 18, 2009


Aries, the Ram Aries, the ram, is a faint pattern marked by...


©2014 The University of Texas McDonald Observatory