Date: February 20, 2010

Title: Mars and the Red Stars


Podcaster: Tavi Greiner

Organization: A Sky Full of Stars –

Description: Tavi Greiner offers a tour of the “red stars” surrounding Mars in the winter sky.

Bio: Tavi Greiner is a co-creater of A Sky Full of Stars, a co-host of the Deep Sky Divas, and an outreach director for Astronomy.FM. She is also a former Program Manager for Slooh*Radio and a former producer/host of Astrocast.TV’s The Night Sky.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Astronomy.FM, a group dedicated to astronomy education and outreach through their live radio broadcasts, Amateur Astronomy Photo of the Day feature and more. Visit and listen in at


Hello and Welcome to this episode of 365 Days of Astronomy, Mars and the Red Stars, February 20, 2010. My name is Tavi Greiner and I am a co-creator of A Sky Full of Stars, a co-host of The Deep Sky Divas, and an outreach director for Astronomy.FM.

So often, we take a moment for the bigger sky events, like the crescent Moon with a planet, or a bright flyover of the International Space Station; but how often do we take a little time for the rest of the sky and all of those distant stars that appear as little more than twinkling points of light.

While these objects may not appear as spectacular as a conjunction or astronauts flying over our homes, they are equally fascinating, and, better yet, we need not wait for any specific moment to see them. They are always there, waiting for us to explore.

If you’ve been watching Mars this winter, you may have noticed several red and orange stars in its neighborhood. With some simple direction, or using the sky maps I’ve included in the transcript, you can quickly identify each of these stars. But knowing their names is only half of the fun. What are those red and orange stars, and how do they compare to our own Sun?

To begin, we are speaking of extraordinary stars – giants ranging in size from 8 to 1,000 times the radius of our Sun. Not only are they huge, these stars are extremely bright – as much as 50,000 times more luminous than the Sun.

We’ll start with the most obvious, the famous Betelgeuse – a red supergiant located more than 600 light-years away in the constellation Orion. One of the largest, most luminous stars known, Betelgeuse is nearly 1,000 times the diameter of our sun. Though only a few million years old, this star is in a final stage of its life, one in which its outer atmosphere is expanding and contracting – and one not unsimilar to the eventual fate of our Sun. The difference, however, is that Betelgeuse will likely soon end as a giant explosion – a supernova – and possibly even as a neutron star or a black hole. Our Sun, on the other hand, will simply expand, dispelling its outer layers, until little remains but a small bright hot dwarf – and that end is billions of years away.

Our next star, Pollux, or Beta Geminorum, is Gemini’s brightest star and is the closest of our little red group. This orange-red giant measures about 9 times the radius of our sun and is located some 34 light-years away. You’ll find it right next to its not-so-identical twin, Castor, both of which represent the heads of mythological twins. The really exciting thing about Pollux is that it is known to host at least one planet – a Jupiter-class object, Pollux b – which orbits its host at about the same distance that Mars orbits the Sun.

If you aren’t familiar with the constellation Gemini, Pollux and Castor are the bright pair southeast of Betelgeuse on your E horizon after sunset, or directly above Betelgeuse on your west horizon before sunrise. They also happen to be just above Mars in the evening and beneath it in the morning.

Capella, Auriga’s brightest star, is a yellow-orange giant located about 42 light-years away. This bright beauty is actually comprised of four individual stars – two Class-G giants and two red dwarfs. The two giants orbit each other at a distance comparable to Venus and the Sun, while the two dwarfs orbit each other nearly a light-year, or about 6 trillion miles, away from the larger pair.

You can find Capella directly above Castor and Pollux, high on your east horizon after sunset, or as the right-side point of a triangle with Pollux and Betelgeuse, on your west horizon before sunrise.

Last, but not least, there is the eye of Taurus, Aldebaran – an orange giant surrounded by a bright sprinkling of stars known as Hyades. While Aldebaran may seem a member of this little group, it is actually a single foreground star residing some 90 light-years closer than the cluster. Hyades, on the other hand, is a collection of about 350 stars, the brightest of which form the little triangle asterism beside Aldebaran. One of those stars, Epsilon Tauri, (itself an orange giant and also known as the Bull’s eye) is host to a gas-giant planet nearly eight times the size of Jupiter. Of course, not even the largest planets can compare to the star, Aldebaran. It is the most luminous star within 100 light-years of our Sun, and so large that were it our Sun, it would span 20° of the sky – that’s 40 times the apparent size of the Full Moon – or about two of your fists held side-by-side at arm’s length.

Aldebaran is easy to spot – it’s that bright orange star between Orion’s Betelgeuse and the Pleiades star cluster in Taurus.

Using each of these bright stars as starting points, explore the surrounding sky through a pair of binoculars. You’ll find a delightful array of celestial treats, including a bright nebula in Orion’s belt stars beneath Betelgeuse, that Hyades star cluster with Aldebaran, and the eclipsing system, epsilon Aurigae, just west of Capella. And, of course, don’t forget about Mars. You’ll find it just a few degrees from the famous Beehive Cluster all winter and with the waxing gibbous moon on the 25th of this month and the next.

And there you have it – a few tidbits to enhance your stargazing. Now grab a star chart, a pair of binoculars, and head outside for a night with Mars and the red stars.

Star Charts:

MarsStarsGraphic –

AnimatedSkyChart –

AldebaranHyadesGraphic –

Orion NebulaGraphic –

epsilonAurigaeGraphic –

MarsBeehiveGraphic –

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.