CANCER, THE CRAB

Taranaki Daily News, 26 March 1932, Page 11 (Supplement)

CANCER, THE CRAB

A SWARM OF SUNS

(By

Rev. B. Dudley, F.R.A.S.)

At such times as will enable readers to observe them with the utmost convenience, attention is being directed in these articles to the I'2 successive zodiacal constellations. These occasions arrive when they reach the northern point well after darkness has set in on moonless nights. We are now to take a look at Cancer, the Crab, the most inconspicuous of the entire series, though one of the most -interesting. Mythically considered, Cancer represents the crab sent by the goddess Juno to distract Hercules during his combat with Hydra, the many-headed dragon, by pinching his toes. Hercules, however, crushed the crab with a single blow; but Juno rewarded the faithful creature by according it a place in the heavens. Hydra is represented as a constellation of very great length, extending from a point a little to the south of Cancer, where a group of faint stars marks the head, to the south, and south-east in a long line of feeble stars, passing in its course immediately south of Crater (the Cup) and Corvus (the Crow), two small constellations above Leo (the Lion), which are sometimes called its riders. It continues ibs straggling way above the entire length of the long, trailing constellation Virgo (the Virgin). The ancient Egyptians represented the group, not as a crab but a beetle, while the Chaldeans called it the “gate of ■men,” through' which souls descended on their way to join human bodies upon earth. Capricornus was correspondingly the “gate of the gods,” because they considered that the liberated souls of men went through it on their flight to heaven. 'J Centuries ago the Sun attained its greatest distance north of the equator at the time when it was passing through the constellation of Cancer. Our tropic of Cancer, which marks the northern limit of' the torrid zone, received its name from this fact. At the time when the sun reaches the point farthest north its height above the horizon changes but very little from day to day, and for a short time it appears to be slowly crawling sideways across the heavens, as a crab walks. For this reason, _it has been suggested, the constellation was called Cancer, the Crab.. Owing to the “precession of the equinoxes,’’ or westward .shifting of the vernal equinox —the point where the equator passes •north in spring—the sun, when it is ■farthest north, is brought into Gemini. (Precession would in turn, after the lapse ■pi centuries, cause the sun to pass into yet another constellation at the beginning of summer. The two stars Gamma and Delta in the Crab, form the centre .of an interesting area as viewed in a field glass. About midway between these stars, and a little to the. west, is the cluster “M 44 known as Praesepe, though it is more popularly called the Beehive or Manger. The cluster suggests a hive of bees, because of its swarming multitude of stars (about 150 in all)., It was one of the discoveries of Galileo that, instead of being a nebula, it is really a star-cluster. Alpha, its brightest star, is a double, which requires a good telescope to resolve. lota is another equally interesting double-star, one of the pair being orange and the other blue in colour. .The components are close to each other and are of 4J and 5 J magnitudes respectively. lota is considered a' fine example of contrast in the components of a double. ’ The star Zeta in ■Cancer is composed of three yellow suns which, together, form one system, physically united by gravitational ■bonds.

To-day the Crab will be due ■north at about 8.30 p.m. The one feature by which it may be certainly distinguished is the Beehive, which to the naked sight appears as a faint patch of luminosity containing three or four individual stars, no brighter than the rest of the constellation. At the present time fortunately the planet Jupiter is ■shining with great lustre just a little to the right or east of the Beehive, and may therefore be taken as a guide to its whereabouts. .'Jupiter itself cannot be mistaken because, like Venus in the west, it is the brightest star that adorns the east, rising in daylight. But although this planet makes a reference star by which the group may be found, its excessive brilliancy dominates the skies in that region and puts the cluster and the entire constellation of which it is part into the shade. If the reader ■knows where to find the two bright •stars, Pollux (in Gemini) and Regulus ■(in Leo) and will draw a straight line ■from one to the other, that line will •pass through Cancer, Praesepe being nearly half the distance." Among the ancients Praesepe was regarded as a harbinger of weather conditions. Aratus of Soli, an early astronomer and poet, wrote in reference to ■this cluster—

“A murky manger, with both stars 'Shining unaltered, is a sign of rain. If while the northern ass is dimmed By vaporous shroud, he of the south _ .gleam radiant, Expect a south wind; the vaporous shroud and radiance

Exchanging stars, harbinger Boreas.”

There was more than mere superstition in this. The dimness of the cluster is an indication that vapour is gathering and condensing in the atmosphere, just as a ring around the moon is taken as sign of the same accumulation and condensation of vapour that precedes a storm. The poet’s reference to the •“murky manger” and the “asses” requires explanation. On either side of Praesepe are two stars once called As■elli, the Asses. The hazy-looking cloud between was. the Manger. Aratus advises his readers to —

“Watch the Manger like a little mist, Far north in Cancer’s territory it

floats. Its confines are two faintly glimmering stars; These are two asses that a manger ' parts, Which suddenly when all the sky is

clear 'Sometimes quite vanishes, and the

two stars. Seem to have closer moved thei- sundered orbs.”

For some years after T 859 existed a suspicion that an inner planet might yet be found nearer the sun than Mercury. A close scrutiny was made; but eventually the search was abandoned. During a total eclipse •of the Sun in 1878, however, Professor Watson revived the question by announcing that he had seen two star-like objects near the Sun. Was one of these the longsought plauet “Vulcan”? These objects turned out . to be the two stars Theta and Zeta in the constellation of Cancer. No one now looks for an inter-Mercurial world, '■