The Olympics in Sydney, Australia ended this past Sunday. For those of you who saw some of the games on the tube, you were perhaps introduced to a number of things you wouldn't encounter in the states. If you were there in person and went to the "outback" where the skies are dark and often cloud free, you might find yourself a bit disoriented. For one thing, there's no Big Dipper to help guide you to the North Star. Still, there's plenty to see. We tend to be chauvinistic here in the US in regards to most things. It's easy to believe that we have it better than others, and in most cases it's probably true.

Is our night sky more interesting than the sky in the Southern Hemisphere? Let's say you're viewing the sky from 35 degrees north latitude one night, east of Albuquerque near Clines Corner, New Mexico, and the next night you're at 35 degrees south latitude, just west of Australia's capitol of Canberra, near the city of Wagga Wagga.

At first glance, it might seem hard for the Southern Hemisphere to compete with what we can see at night. We're able to observe the Big and Little Dippers and the North Star (Polaris) throughout the year, and perhaps the most conspicuous of all constellations, Orion the Hunter, is visible in the evening from late fall through early spring. Additionally, fifteen of the twenty brightest stars are visible from the Northern Hemisphere, including the brightest star in the sky - Sirius (magnitude -1.6) in Canis Major, Capella (magnitude 0.2) in Auriga the Chariot, the Arcturus (magnitude 0.2) in Bootes the Kite, and the red giant Antares in Scorpion, We also have the "summer triangle" - the three bright stars of Vega, Altair and Deneb form an isosceles triangle. Vega is the very bright (0.1 magnitude) white star in the constellation Lyra the Lyre, Altair is the bright (0.9 magnitude) star in Aquila the Eagle and Deneb is the brightest star in Cygnus the Swan (1.3 magnitude), which is also known as the Northern Cross. Take a look for the "summer triangle" if you get a chance. It's nearly overhead now at about 10:00 in the evening. By the way, the brightest stars have the most negative magnitudes, and a star with a magnitude of 0.0 is approximately 2.5 times brighter than a star having a magnitude of 1.0.

My guess is that if you were asked to name a constellation visible only from the Southern Hemisphere, you would be hard pressed to name one, though you might be able to think of the Southern Cross. Do you remember the song Southern Cross by Crosby, Stills and Nash?

"When you see the Southern Cross for the first time,

You'll understand now why you came this way"

The Southern Cross is indeed a brilliant constellation consisting of several bright gems in the shape of a cross - more or less. The brightest is Alpha Crucis (magnitude of 1.1), which is actually a triple star system. One of the stars is about 650 times as bright as our Sun and another is almost 1,000 times as bright. Beta Crusis (magnitude 1.5) is a blue star, and Gamma Crusis, at the head of the cross, is an orange colored second magnitude star. The star denoting the right-most corner on the cross (Delta Crusis) is the faintest of the four (third magnitude). Perhaps only the magnificent Orion has three bright stars that appear to be so close to each other. The Northern Cross pales in comparison to its southern counterpart.

While over 50 countries have stars on their flags ( yes, the US has the most), only three countries, I believe, have flags with constellations. An argument about the status a particular arrangement of stars has can be made if it's used as a nation's symbol. Papua New Guinea, New Zealand, and Australia each has the Southern Cross emblazoned across its banner. It should be noted that the state of Alaska has the Big Dipper and North Star on its flag.

From both hemispheres, we can see all of the constellations of the Zodiac, at different times of the night or in different seasons. These constellations mark the course of the Sun throughout the year and are positioned close to the celestial equator (the projection of the Earth's equator onto an imaginary hollow sphere that surrounds the Earth). Therefore, they're visible in the northern part of the sky from Australia and visible in the southern portion of the sky in North America. At about 40 degrees north or south latitude, almost 1/2 of the stars in the other hemisphere are visible. So, most of the people in the US can see most of the stars in the Southern Hemisphere. However, at 40 degrees north, the stars overhead for an observer at 40 degrees south, are too close to the southern horizon to be easily recognized. Nonetheless, if you live in southern Florida, southern Texas or Hawaii, you should be able to make out the Southern Cross in May and June.

What else can we see down in the Southern Hemisphere? Well, while from Clines Corner, 15 of the 20 brightest may be seen throughout the course of the year, in Wagga Wagga, 17 of the 20 brightest can be seen. Each of the three brightest stars visible from Earth can be observed from the Southern Hemisphere; Sirius, Canopus (magnitude -0.9) in the constellation Carina the Keel and Alpha Centaui (magnitude 0.1) in the constellation Centaur. Canopus and Apha Centauri can be seen only from the Southern Hemisphere. Moreover, the closest star to Earth (Proxima Centauri), just 4.2 light years away, is also found in Centaur, though it's much too faint to be seen with the unaided eye.

In both hemispheres, the disk of our own Milky Way Galaxy can be seen as a fragmented whitish band that stretches across the night sky. From the Northern Hemisphere, in places far removed from city lights, we're also able to see the Andromeda Galaxy, which is the furthest thing visible to us without the aid of magnification (about 2 million light years distant). You can see it now, northeast of the Great Square of Pegasus - consult a star map for precise directions. In the Southern Hemisphere, however, two small galaxies are visible, the large and small Magellanic Clouds, likely satellite galaxies to our own Milky Way. As you might have surmised, the Portuguese navigator, Fernando Magellan, sighted these "clouds" as he explored the southern seas. While they're not as faraway or as big as the Andromeda Galaxy, these faint patches of light are easier to see, since they're considerably closer (about 150,000 light years distant). The Southern Cross points in the direction of the Lesser Magellanic Cloud. In 1987, a supernova suddenly appeared in the Lesser Magellanic Cloud, and it was visible with the unaided eye, to sharp-eyed observers, for a few months .

So there's a lot to see "down under" even when you're looking up. It's hard to say if one hemisphere has a better view than the other. It depends on what you're looking for. In general, there's less light pollution in the Southern Hemisphere, thus viewing fainter celestial objects may be somewhat easier than up north. If you ever venture to the Southern Hemisphere, maybe you'll understand why it was you came all that way - in the Southern Cross.

For more about this see most any astronomy text book or even Zim and Bakers Stars - a Golden Nature Guide.

Also visit the Abrams Planeterium web site at http://www.pa.msu.edu/abrams/diary.html and the Astronomy Picture of the Day web site at http://antwrp.gsfc.nasa.gov/apod/ap960503.html

05 October 2000