Astronomy in a nutshell

by Garrett Putman Serviss

Fig. 19. Key to North Circumpolar Stars.

Only the conspicuous stars have been represented in the chart, just enough being included to enable the learner to recognise the constellations by their characteristic star groups, from which they have received their names. The chart extends to a distance of 40° from the pole, so that, for observers situated in the mean latitude of the United States, none of the constellations represented ever descends below the horizon, those that are at the border of the chart just skimming the horizon when they are below the pole.

On the key to the chart the Greek-letter names of the principal stars have been attached, but some of them have other names which are more picturesque. These are as follows: In Ursa Major (the Great Bear, which includes the Great Dipper), α is called Dubhe, β Merak, γ Phaed, δ Megrez, ε Alioth, ζ Mizar, and η Benetnash. The little star close by Mizar is Alcor. In Cassiopeia, α is called Schedar, β Caph, and δ Ruchbar. In Ursa Minor, the Little Bear, α is called Polaris, or the North Star, and β Kochab. In Draco, α is called Thuban, and γ Eltanin. In Cepheus, α is called Alderamin, and β Alfirk. These names are nearly all of Arabic origin. It will be observed that Merak and Dubhe are the famous “Pointers,” which serve to indicate the position of the North Star, while Thuban is the “star of the pyramid,” before mentioned. The north celestial pole is situated almost exactly on a straight line drawn from Mizar through the North Star to Ruchbar, and a little more than a degree from the North Star in the direction of Ruchbar. This furnishes a ready means for ascertaining the position of the meridian. For instance, about the middle of October, Mizar is very close to the meridian below the pole, and Ruchbar equally close to it above the pole, and then, since the North Star is in line with these two, it also must be practically on the meridian, and its direction indicates very nearly true north. The same method is applicable whenever, at any other time of the year or of the night, Mizar and Ruchbar are observed to lie upon a vertical line, no matter which is above and which below. It is also possible to make a very good guess at the time of night by knowing the varying position of the line joining these stars.

The star Caph is an important landmark because it lies almost on the great circle of the equinoctial colure, which passes through the vernal and autumnal equinoxes.

On the key, the location of the North Pole of the Ecliptic is shown, and the greater part of the circle described by the north celestial pole in the period of 25,800 years.

While the reader who wishes to pursue the study of the constellations in detail must be referred to some of the works before mentioned, or others of like character, it is possible here to aid him in making a preliminary acquaintance with other constellations beside those included in our little chart, by taking each of the months in turn, and describing the constellations which he will see on or near the meridian south of the border of the chart at the same time that the polar constellations corresponding to the month selected are on or near the meridian in the north. Thus, at 9 P.M. about the first of January, the constellation Perseus, lying in a rich part of the Milky Way, is nearly overhead and directly south of the North Star. This constellation is marked by a curved row of stars, the brightest of which, of the second magnitude, is Algenib, or α Persei. A few degrees south-west of Algenib is the wonderful variable Algol. East of Perseus is seen the very brilliant white star Capella in the constellation Auriga. This is one of the brightest stars in the sky. Almost directly south of Perseus, the eye will be caught by the glimmering cluster of the Pleiades in the constellation Taurus. A short distance south-east of the Pleiades is the group of the Hyades in Taurus, shaped like the letter V, with the beautiful reddish star Aldebaran in the upper end of the southern branch of the letter. The ecliptic runs between the Pleiades and the Hyades. Still lower in the south will be seen a part of the long-winding constellation Eridanus, the River Po. Its stars are not bright but they appear in significant rows and streams.

About the first of February the constellation Auriga is on the meridian not far from overhead, Capella lying toward the west. Directly under Auriga, two rather conspicuous stars mark the tips of the horns of Taurus, imagined as a gigantic bull, and south of these, with its centre on the equator, scintillates the magnificent constellation Orion, the most splendid in all the sky, with two great first-magnitude stars, one, in the shoulder of the imaginary giant, of an orange hue, called Betelguese, and the other in the foot, of a blue-white radiance, called Rigel. Between these is stretched the straight line of the “belt,” consisting of three beautiful second-magnitude stars, about a degree and a half apart. Their names, beginning with the western one, are Mintaka, Alnilam, and Alnitah. Directly under the belt, in the midst of a short row of faint stars called the “sword,” is the great Orion nebula. It will be observed that the three stars of the belt point, though not exactly, toward the brightest of all stars, Sirius, in the constellation Canis Major, the Great Dog, which is seen advancing from the east. Under Orion is a little constellation named Lepus, the Hare.

The first of March the region overhead is occupied by the very faint constellation Lynx. South of it, and astride the ecliptic, appear the constellations Gemini, the Twins, and Cancer, the Crab. These, like Taurus, belong to the zodiac. The Twins are westward from Cancer, and are marked by two nearly equal stars, about five degrees apart. The more westerly and northerly one is Castor and the other is Pollux. Cancer is marked by a small cluster of faint stars called Præsepe, the Manger (also sometimes the Beehive). Directly south of the Twins, is the bright lone star Procyon, in the constellation Canis Minor, the Little Dog. Sirius and the other stars of Canis Major, which make a striking figure, are seen south-west of Procyon.

The first of April the zodiac constellation Leo is near the meridian, recognisable by a sickle-shaped figure marking the head and breast of the imaginary Lion. The bright star at the end of the handle of the sickle is Regulus. Above Leo, between it and the Great Dipper, appears a group of stars belonging to the small constellation Leo Minor, the Little Lion. Farther south is a winding ribbon of stars indicating the constellation Hydra, the Water Serpent. Its chief star, Alphard, of a slightly reddish tint, is seen west of the meridian and a few degrees south of the equator.

At the beginning of May, when the Great Dipper is nearly overhead, the small constellation Canes Venatici, the Hunting Dogs, is seen directly under the handle of the Dipper, and south of that a cobwebby spot, consisting of minute stars, indicates the position of the constellation Coma Berenices, Berenice's Hair. Still farther south, where the ecliptic and the equator cross, at the autumnal equinox, is the large constellation Virgo, the Virgin, also one of the zodiacal band. Its chief star Spica, a pure white gem, is seen some 20° east of the meridian. Below and westward from Virgo, and south of the equator, are the constellations Crater, the Cup, and Corvus, the Crow. The stars of Hydra continue to run eastward below these constellations. The westernmost, Crater, consists of small stars forming a rude semicircle open toward the east, while Corvus, which possesses brighter stars, has the form of a quadrilateral.