The Life of a Star: Red Giants

How does a star become a red giant? Find out on today's episode of Astro Minute!

What is Astro Minute?

Welcome to the Astro Minute! I'm Lauren Smyth, and with the help of astronomer and teacher Kelli Smyth, I'll be your tour guide as we explore the secrets of the night sky sixty seconds at a time.

Welcome to the Astro Minute, where we’re exploring the universe sixty seconds at a time. I’m Lauren Smyth, and today we’re looking at the old age of low- and medium-mass stars.

When the core of a less massive star runs out of hydrogen to fuse, its gas and radiation pressure outward decrease, the inward pull of gravity takes over, and it begins to collapse. The core then becomes denser and heats up, igniting helium fusion within it. The core’s helium fusion then heats up the surrounding shell of gas and ignites hydrogen fusion in it, which causes the outer gas of the star to expand to hundreds of times our sun’s diameter and cool to a red glow. The star is now a red giant. Our sun will some day enter this phase, expanding beyond Venus’s orbit and possibly beyond Earth’s.

To see red giants visible naked eye, look for Arcturus, Aldebaran, and the twin star Pollux.

I’m Lauren Smyth, and that’s your AstroMinute.