Stars of the southern skies

by M. A. Orr

There are more bright stars in the southern hemisphere than in the north, for a count of all those above fourth magnitude shows that there are 228 south of the equator against only 164 north. But whereas the stars in the north are fairly evenly distributed, there is a more strongly marked tendency in the south to congregate on the Milky Way, so that, while the tract through Argo and the Cross to Scorpio and Sagittarius is extraordinarily rich, the part between Orion and Fomalhaut is comparatively dark and bare, and the regions round the south pole and north of Argo are also very barren of bright stars. Some regions, however, which look dull to the eye abound in marvels for the telescope and camera.

The brilliance and the complex structure of the Milky Way is undoubtedly what most strikes the northerner travelling south. In England we have a glimpse of it in Cygnus and Aquila, where this rich and bright part begins; but there is nothing to equal the brightness or the mingling of dark and light which we see in Argo and near the Cross, in Scorpio and in Sagittarius. When this part is about to rise, there is often a glow on the horizon as if it were dawn.

III
THE TEN BRIGHTEST STARS OF THE
SOUTHERN HEMISPHERE

The brighter of the two Pointers to the Cross, Alpha Centauri, ranks very high among first-magnitude stars, though it is excelled in brightness by Sirius and Canopus; but its greatest claim to our interest is that among all the host of stars it is our nearest neighbour. Yet, should we decide to pay a visit and travel with the speed of light (11 million miles a minute), it would be four years and three months before we could reach our destination—so great are the spaces which separate our sun with his family of planets from the nearest of his brother suns.

Alpha Centauri is also interesting as a double star. The two components are nearly equal in brightness, and are seen as a brilliant yellow pair in quite a small telescope. It was one of the first doubles known, being discovered as such in 1689; and Herschel calls it a “superb double star, beyond all comparison the most striking object of the kind in the heavens.” The two stars he describes as “both of a high ruddy or orange colour, though that of the smaller is of a somewhat more sombre and brownish cast.”

All stars are suns, but they vary so much in brightness and size and quality of light that it is as difficult to match two stars in the sky as two trees in a wood. Yet one of this pair is an almost exact counterpart of our sun. The pair is approaching us, and at the same time revolving one about the other in a period of about eighty years.

The other Pointer, Beta Centauri, is a star very different from our sun. It belongs to a type called “Orion stars” because so many are found in that constellation. Instead of shining with a yellow light, they are blue or bluish-white, and their glowing atmospheres contain quantities of helium, the gas which was only recently discovered on earth though it had been known for many years in the sun. Oxygen and nitrogen and some yet unknown elements are also present.

Alpha Crucis, the brightest star of the Cross, is also a blue Orion star, and the telescope shows it to be triple. There are two bright twin stars, and a fainter one which would be just visible to the naked eye if alone, but being overpowered by the brilliance of the bright pair can only be seen in a large telescope. Quite a small telescope will separate the twins.

Achernar, the Last-of-the-River, is also an Orion star, 75 light-years distant from us—i.e. light takes 75 years to come from it to us. The sun if removed to a third of this distance would be barely visible to the naked eye.

Rigel, Orion’s foot, is the brightest star of this class. Its intrinsic brilliancy and its size must be enormous, for its distance is certainly more than 360 light-years, and may be greatly more. And the distance is increasing at the rate of 39 miles a second. Rigel is also a double star, but its companion is very faint. In an 8-inch telescope the bright star looks white or pale lemon-yellow, contrasting beautifully with the little companion which is blue.