Mission 2: Eye of the Scorpion

August 18, 2009

Mission Objectives: Bright star, Constellation

Equipment: Naked eye

Required Time: 1 minute

Instructions: Go outside after dark and look south. Look for a distinctly reddish or orangey star above the southern horizon. To the right of it you will see three bright stars making a short vertical arc.

Antares in Stellarium, as it appears right after sunset in the southern part of the US.

Antares in Stellarium, as it appears right after sunset in the southern part of the US.

The red star is Antares, a red supergiant star about 600 light years away. It is an immense star, with a diameter about 800 times larger than that of the sun. If you placed Antares at the center of our solar system, it would swallow Mercury, Venus, Earth, and Mars.

Antares comparison

Antares compared to another large star, Arcturus, and the sun. R stands for 'radius'. Image from Wikipedia.

Antares is near the end of its life. Smaller stars, like our sun, eventually turn into red giants and blow off most of their mass to form planetary nebulae (so named because the near-spherical balls of gas look  like planets in telescopes, not because they actually have anything to with planets), each with a white dwarf at the core. No such “out with a whimper” fadeout for Antares–one of these days it will suffer a core collapse and blow itself apart as a Type II supernova. When this happens, the explosion will briefly outshine the entire Milky Way galaxy. Fortunately, “one of these days” could be thousands or even millions of years from now, so there’s no cause for panic.

We’re actually catching Antares pretty late in the season. The best time to see it is in late May and early June, when it is exactly opposite the sun in the sky. That means it rises at sunset, sets at dawn, and is highest in the sky in the middle of the night. I don’t know about you, but I’m not up very often at those wee hours. By August, Antares is high in the sky at sunset, or as high as it’s going to get.

Here’s the rub: Antares is pretty far south, so observers in the US and Europe need a clear southern horizon to see it. And the farther north you are, the worse your chances get. Here’s what Antares looks like just after sunset in southern England (higher and to the east you can see Altair, which I’m sure you remember from Mission 1).

Antares just after sunset from southern England.

Antares just after sunset from southern England.

Antares is also known as Alpha Scorpii, because it is the brightest star in the constellation Scorpio. The three bright stars to the right of Antares are supposed to be the scorpion’s claws, and the J-shaped hook of stars trailing off to the south and east form its body and tail, complete with a stinger on the end. To see the body and tail I have to take a short walk. From my tree-shrouded driveway all I can see are the claws and the giant red eye, as terrifying in life as it is in mythology.

The constellation Scorpio as it appears from the southern US.

The constellation Scorpio as it appears from the southern US.


  1. Done!

    Not dark enough for the whole constellation, but I did see nearby Al Niyat and HIP 81266

  2. […] Related Missions: Eye of the Scorpion […]

  3. […] started out facing south, down the mountain, toward Scorpio and Sagittarius. Those are two of the most recognizable constellations, Scorpio because it actually […]

  4. […] so large that they could swallow the entire inner solar system. Betelgeuse in Orion and Antares, the glaring red eye of Scorpio, are red hypergiants, and respectively the eighth and sixteenth […]

  5. if your looking at the constellation scorpio, then look 10-15 degrees horizontally to the right what 3 bright stars are almost in line vertically [much like Orions Belt]?

  6. Hi John,

    Good question–I should have mentioned the answer in the post! Those three bright stars that form the “claws” of the scorpion are, from north (top) to south (bottom), Graffias (Beta Scorpii), Dschubba (Delta Scorpii), and Iclil (Pi Scorpii). Interestingly, all three of these are actually multiple star systems, although only Graffias is easily splittable with small telescopes. Nu Scorpii is just east and a bit north of Graffias, and Omega Scorpii is south-southeast of Graffias; both of these are wide doubles that can be split with binoculars.

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