Thursday, August 09, 2007

Cosmic Scorpion

Although I haven’t acquired a reasonable view of the Ring Nebula in my small telescope, this still has been an exciting astronomy month for me. This month I got a reasonably good view of a constellation that was new to me, Scorpius, the zodiac constellation of the Scorpion.

At Chicago’s latitude, Scorpius never rises very high above the southern horizon and I’ve never lived anywhere with good southern exposure. Stars near the horizon are usually hard to see even with a good view because there is more atmosphere to penetrate and more light pollution. This month, however, observers get a helping hand from the giant planet Jupiter which is currently in Scorpius, providing a cosmic signpost of where to look in the southern sky.

(You can find out stuff like that from astronomy magazines like ‘Sky & Telescope’ or ‘Astronomy’—they both include monthly columns describing which planets are visible in the morning or evening and which constellations they’re in.)

My birth sign is Scorpio, so I’ve always wanted to track down the constellation Scorpius. Like many astronomy buffs I have no particular belief in astrology, but astrology and astronomy will always be linked in the same manner as alchemy and chemistry.

Scorpius is a beautiful constellation, dominated by the fire-red giant star Antares. And, unlike many constellations which appear to be vague patterns in the sky, Scorpius actually does resemble a scorpion, once you get the hang of picking out its key stars.

The photograph above was taken in Chile and Scorpius is at a slightly different angle than we normally see it in our south sky, but the photograph captures the constellation beautifully. Antares appears pinkish, just to the right of the center of the photograph. The head and claws of the scorpion are the half-dozen blue-white stars curving up and down along the right edge of the photo. The scorpion’s ‘tail’ goes left from Antares and curls down over the Milky Way.

There is an interesting overlap between the mythology of the scorpion and the science of Scorpius.

According to Mediterranean myths, Scorpius is the scorpion that stung and killed Orion, the hunter. When the gods put them both in the heavens, the gods placed them at opposite positions on the celestial sphere to avoid future fights.

In real-life, although the stars making up Scorpius and the stars making up Orion exist in very different portions of the Milky Way galaxy, they share some intriguing characteristics. Both constellations are made up of actual groups of stars. They are not stars which appear close because of our point-of-view on Earth. The stars of Scorpius are mostly of a similar type of hot, blue-white stars and they are believed to have formed at about the same time and within the same region of space. The same is true of Orion, with most of the stars also being hot, blue-white stars occupying the same region of space. These two different regions of the Milky Way galaxy with similar groups of hot, blue-white stars share another characteristic: Within each region, one of the stars has either evolved faster than the others or was ‘born’ a few million years earlier than the others. Each region is dominated by a ‘red giant’ type star which presents a beautiful visual contrast to the area’s blue-white stars. Antares in Scorpius, and Betelgeuse in Orion.

So, mythology has linked these two groups of stars on opposite sides of the sky, and they actually do have scientific characteristics in common.

There’s another, more esoteric reason to check out Scorpius.

The tail of the scorpion hangs down over the galactic equator, the horizontal center-line of the Milky Way galaxy. And, if you look just east of the tail, just behind the scorpion, you are looking (more or less) right at the actual center of the Milky Way. Interstellar dust lanes prevent us from seeing the actual halo of ancient stars at the center of the Milky Way, but if you sweep over this area with binoculars under dark skies—that is, away from city lights!—you actually see a view similar to the above photograph, rich with the Milky Way’s stars, star clusters and nebulae.

Our solar system, the Sun and its planets including the Earth, is off to the side of our galaxy. We’re out in the fringes of one of the spiral arms of the Milky Way. All the really cool civilizations—civilizations where the women look like Anna Kournikova and the men look like Steve McQueen—are probably many hundreds of light years in that direction . . .

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