Quest for the Southern Cross

When I first learned the constellations as a boy growing up in Corpus Christi, Texas, (latitude 28°N), I was intrigued by the fact that there was a sizeable portion of the sky below my southern horizon that I never saw.


The Southern Cross, looking south from latitude 25° N on May 24-25.

Rumor had it, though, that from my latitude you could see the northernmost stars of the Southern Cross, also known as Crux, in mid-April around 10 o'clock.

I confirmed this for myself one clear April evening from the flat grain fields west of the city. In case you don't know, portions of coastal south Texas are remarkably flat and, save for the occasional red-blinking antenna beacon and lonely mercury-vapor yard light, horizons in the country are generally unobstructed. It is not unusual, when the air is transparent, to see stars within a degree or two of the horizon line itself.

In fact, there are many accessible locations in the Western Hemisphere where one can see a few extreme southern stars: south Texas, the Florida Keys, the Baja Peninsula, the west coast of Mexico, the Yucatan, and locales in the Caribbean and Hawaii.

If you find yourself in one of these southerly regions this spring, you might begin your southern sky quest by looking for the northernmost stars of the Southern Cross. The torqued square of stars forming Corvus the Crow, which hangs fairly high in the sky due south around 10 o'clock this week, makes an excellent signpost for this southern group. The Cross lies 40° below (or due south of) Corvus. Thus when the Crow flies high, the Cross is nigh. Just lower your sight to just above the horizon and look for a triangle of stars - the three northernmost stars of the Cross. (Be sure you have an unobstructed horizon.) The brightest star of the three, lying furthest east, is Mimosa, named after the tropical shrub. To see the Cross's brightest and southernmost member, Acrux, you will need to be south of latitude 25° N.

If you wait another hour and a half, you should be able to see the bright pair Alpha (a) and Beta (P) Centauri climb to take the Southern Cross's place. (If you're at latitude 28° N, however, you will only be able to see the northernmost-placed Beta, also known as Hadar, as it peeks briefly above the horizon.)

Alpha and Beta Centauri are ensconced deep in the southern Milky Way. Scan this area and the region north and northwest with binoculars, and you will see many 'clouds' of stars. One very noticeable object looks like a star to the naked eye, but in binoculars appears distinctly 'woolly.' Closer inspection with a telescope reveals this to be the great globular cluster Omega (ra) Centauri, a sphere of millions of gravitationally bound stars, and one of the most magnificent sights in the sky.

These are only a few jewels spilled from a chest of riches. The southern sky harbors countless bright stars, clusters, nebulae, and, most notably, the Large and Small Magellanic Clouds, the Milky Way's neighboring galaxies (February 8 - 14). If you can't travel to the Southern Hemisphere anytime soon, the next best thing is to find yourself in the southerly realms of the Northern Hemisphere this spring where you can catch tantalizing sights of the celestial vistas on the 'other side' of the universe.

Also this week:

• Around 10 o'clock, look south of the Big Dipper's handle for a lone, tenuous 'cloud' some ten full-Moon widths in apparent diameter. Binoculars reveal a few parallel threads of stars all about the same brightness. This is the Coma star cluster, one of the best known and well-studied open star clusters in the sky, because it is so nearby (about 250 light-years). The star strands make up the 'hair' in the constellation Coma Berenices, Berenice's Hair.

• The Scorpiid/Sagittariid meteor shower is active between April 15 and July 25 but peaks during this week each year. The shower can yield as many as 20 meteors per hour, although only under optimal viewing conditions. It is also known to produce the occasional fireball. The radiant is highest around midnight.

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