“Prof. Newcomb rejects the former well-authenticated redness of Sirius, because he cannot explain the fact. But the ink was scarcely dry on his new book on the stars, in which he takes this position, when Nova Persei blazed forth in 1901; and observers saw it change colour from day to day and week to week. Could any one explain the cause of these numerous and conspicuous changes of colour? Shall we, then, deny the changes of colour in Nova Persei, some of which were noticed when it was nearly as bright as Sirius?”[438]
“Prof. Newcomb rejects the former well-authenticated redness of Sirius, because he cannot explain the fact. But the ink was scarcely dry on his new book on the stars, in which he takes this position, when Nova Persei blazed forth in 1901; and observers saw it change colour from day to day and week to week. Could any one explain the cause of these numerous and conspicuous changes of colour? Shall we, then, deny the changes of colour in Nova Persei, some of which were noticed when it was nearly as bright as Sirius?”[438]
On the ceiling of the Memnonium at Thebes the heliacal rising of Sirius is represented under the form and name of Isis. The coincidence of this rising with the annual rising of the Nile is mentioned by Tibullus and Aclian. About 4000B.C.the heliacal rising of Sirius coincided with the summer solstice (about June 21) and the beginning of the rising of the Nile. The festival in honour of this event was held by the Egyptians about July 20, and this marked the beginning of the sacred Egyptian year. On the summit of Mount Pelion in Thessaly there was a temple dedicated to Zeus, where sacrifices were offered at the rising of Sirius by men of rank who were chosen for the purpose by the priests and wore fresh sheepskins.
Sirius seems to have been worshipped by the ancient Egyptians under the name of Sothis, and it was regarded as the star of Isis and Osiris. The last name without the initial O very much resembles our modern name.
According to Al-Sufi, the Arabians called Siriusal-schira al-abûr, “Sirius which has passed across,” alsoal-schira al Jamânija, “the Sirius of Yémen.” He says it is calledal-abûr, “because it has passed across the Milky Way into the southern region.” He relates a mythological story why Sirius “fled towards the south” and passed across the Milky Way towards Suhail (Canopus). The same story is told by Albufaragius[439](thirteenth century). (The story was probably derived from Al-Sufi.) Now, it seems to me a curious and interesting fact that the large proper motion of Sirius would have carried it across the Milky Way from the eastern to the western border in a period of 60,000 years. Possibly the Arabian story may be based on a tradition of Sirius having been seen on the opposite, or eastern, side of the Milky Way by the men of the early Stone Age. However this may be, we know from the amount and direction of the star’s proper motion that it must have passed across the Milky Way from east to west within the period above stated. The Arabic nameal-abûris not, therefore, a merely fancifulone, but denotes anactual fact. The proper motion of Sirius could not possibly have been known to the ancients, as it was only revealed by accurate modern observations.
The little constellation Canis Minor, the Little Dog, lies south of Gemini and Cancer. Small as it is, it was one of the original forty-eight constellations of Ptolemy. In the Greek mythology it was supposed to represent either one of Diana’s hunting dogs, or one of Orion’s hounds. Ovid calls it the dog of Icarus. Others say it was the dog of Helen, who was carried off by Paris. According to the old poets, Orion’s dog, or the dog of Icarus, threw himself into a well after seeing his master perish. The name Fovea, given to the constellation by Bayer, signifies a pit where corn was deposited. This comes from the fact that the rising of the star Procyon (α Canis Minoris) indicated the season of abundance. But Lalande thought it more probable that the idea of a pit came from the Greek σειρὸς, which means a corn store, and that it was confounded with Sirius.
The name of the bright star Procyon (α Canis Minoris) is derived from the Greek προκύων, “the advanced day,” because it appeared in the morning sky before Sirius. Procyon was called by the Hindoos Hanouman after their famous monkey god, from whose tail a bridge is said to have been formed to enable the army of Rama to pass from India to Ceylon. Al-Sufi says that the star wasmarked on the old astrolabes asal-schira al-schamia, “the Syrian Sirius.” It was also called, he says,al-schira al-gumaisa, “the Sirius with blear eyes” (!) from weeping because Sirius had passed across the Milky Way, Procyon remaining on the eastern side. Here we have the same legend again. The proper motion of Procyon (about the same in amount and direction as that of Sirius) shows that the star has been on the eastern side of the Milky Way for many ages past. About 60,000 years hence, Procyon will be near the star θ Canis Majoris, and will then—like Sirius—have passed across the Milky Way.
Argo, the Ship, is a large constellation south of Hydra, Monoceros, and Canis Major. It is called by Al-Sufial-safîna, “the Ship.” It is supposed to represent the first ship ever built. The name is derived from the builder Argo, or from the Greek word ’Αργὸς. This ship is said to have been built in Thessaly by order of Minerva and Neptune, to go on the expedition for the conquest of the golden fleece. The date of this expedition, commanded by Jason, is usually fixed at 1300 or 1400B.C.With reference to the position of this supposed ship in the sky, Proctor says, “It is noteworthy that when we make due correction for the effects of precession during the past 4000 years, the old constellation Argo is set on an even keel, instead of being tilted some 45° to the horizon, as at present whendue south.” He connects Argo with Noah’s Ark.
The brightest star of Argo is Canopus, called Suhaïl by Al-Sufi. It is the second brightest star in the heavens; but it is not visible in northern latitudes. The Harvard photometric measures make it nearly one magnitude brighter than the zero magnitude, about two magnitudes brighter than Aldebaran, and about half the brightness of Sirius. This fine star has been suspected of variable light. Webb says, “It was thought (1861) in Chili brighter than Sirius.” Observing it in the Punjab, the present writer found it on several occasions but little inferior to Sirius, although very low on the southern horizon. From recent observations by Mr. H. C. McKay in Australia, he believes that it is variable to the extent of at least half a magnitude.[440]But it is difficult to establish variations of light in very bright stars. The parallax of Canopus isverysmall, so its distance from the earth is very great, and it must be a sun of gigantic size. According to Al-Fargani, Canopus was called the star of St. Catherine by the Christian pilgrims in the tenth century.[441]It was called Suhaïl by the old Arabians, a name apparently derived from the rootsahl, “a plain”; and Schjellerup suggests that the name was probably applied to this and some other southernstars because they seem to move along a plain near the southern horizon. Al-Sufi says that he measured the latitude of Schiraz in Persia, where he observed, and found it to be 29° 36′; and hence for that place Canopus, when on the meridian, had an altitude of about 9°. Canopus was the ancient name of Aboukir in Egypt, and is said to have derived its name from the pilot of Menelaus, whose name was Kanobus, and who died there from the bite of a snake. The star is supposed to have been named after him, and it was worshipped by the ancient Egyptians.
Al-Sufi does not mention the famous variable star η Argûs, which, owing to the precession of the equinoxes, he might possibly have seenclose to the horizon, if it had been a bright star in his day. It lies between φ Velorum and α Crucis. Both of these stars are mentioned by Al-Sufi, but he says nothing of any bright star (or indeed any star) between them. This negative evidence tends to show that η Argûs was not visible to the naked eye in Al-Sufi’s time. This extraordinary star has in modern times varied through all degrees of brightness from Sirius down to the 8th magnitude! Schönfeld thought that a regular period is very improbable. It seems to be a sort of connecting link between the long period variables and thenovæor temporary stars. It is reddish in colour, and the spectrum of its light is very similar to that of the temporary stars. Whether it willever become a brilliant object again, time alone can tell; but from the fact that it was presumably faint in Al-Sufi’s time, and afterwards increased to the brightness of Sirius, it seems possible that its light may again revive.
The long constellation Hydra lies south of Cancer, Leo, Crater, Corvus, Virgo, and Libra. It was also called Asina, Coluber, Anguis, Sublimatus, etc. In the Greek mythology it was supposed to represent the Lernæan serpent killed by Hercules. According to Ovid, who fixed its acronycal rising for February 14, it had a common origin with Corvus and Crater. Apollo, wishing to sacrifice to Jupiter, sent the Crow with a cup to fetch water. On his way to the well the Crow stopped at a fig tree and waited for the fruit to ripen! Afterwards, to excuse his delay, he said that a serpent had prevented him from drawing the water. But Apollo, to punish the Crow for his deception, changed his plumage from white to black, and ordered the serpent to prevent the Crow from drinking.[442]Hydra was called by Al-Sufial-schudja, “the Serpent, or Hydra.” He says that “it contains twenty-five stars in the figure and two ‘outside’, and its head is to the south of the southern scale of the Balance” (α Libræ). But this is clearly a mistake (one of the very few errors to be found in Al-Sufi’s work), for he goes on to say that the head is composed of four starsforming a figure like the head of a horse, and he adds, “This head is in the middle betweenal-shira al-gumaisa[Procyon] andKalb al-asad[Regulus] the Heart, inclining from these two stars a little to the south.” This clearly indicates the stars δ, ε, η, and σ Hydræ which, with ζ Hydræ, have always been considered as forming the Hydra’s head. These stars lie south of α and β Cancri, not south of Libra as Al-Sufi says (doubtless by a slip of the pen).
Ptolemy’s 12th star of Hydra (α Hydræ) is, Al-Sufi says, “the bright red star which is found at the end of the neck where the back begins; it is of the 2nd magnitude. It is that which is marked on the astrolabe asunk al-schudja, ‘the neck of the serpent,’ alsoal-fard, ‘the solitary one.’” Al-Sufi’s estimate of its brightness agrees well with modern measures; but it has been suspected of variable light. Sir John Herschel’s estimates at the Cape of Good Hope varied from 1·75 to 2·58 magnitude. He thought that its apparent variation might be due to its reddish colour, and compares it to the case of α Cassiopeiæ. But as this latter star is nowknownto be irregularly variable it seems probable that α Hydræ may be variable also. Gemmill found it remarkably bright on May 9, 1883, when he thought it nearly equal to Pollux (1·2 magnitude). On the other hand, Franks thought it nearer the 3rd than the 2nd magnitude on March 2, 1878. On April 9, 1884, thepresent writer found it only slightly less than Regulus (1·3 magnitude). On April 6, 1886, how-ever, it was considerably less than Regulus, but half a magnitude brighter than β Canis Minoris, or about 2½ magnitude. In the Chinese Annals it is called the “Red Bird.” In a list of thirty stars found on a tablet at Birs-Nimroud, it is called “The son of the supreme temple.” Although to the naked eye deserving the name of Alphard or “the solitary one,” it is by no means an isolated star when examined with a telescope. It has a faint and distant companion, observed by Admiral Smyth; and about 25′ to the west of it Ward saw a small double star (8, 13: 90°: 50″). With a 3-inch refractor in the Punjab, I saw a small star of about 8½ magnitude to the south and a little east of the bright star, probably identical with Smyth’s companion. Farther off in the same direction I saw a fainter star, and others at greater distances in the field. There is also a faint star a little to the north. I also saw Ward’s double with the 3-inch telescope.
There is some difficulty in identifying the stars numbered by Ptolemy 13, 14, and 15 in Hydra. Having plotted a map from Ptolemy’s positions (as given by Al-Sufi), I have come to the conclusion that Ptolemy’s stars are 13 = κ Hydræ; 14 = υ; and 15 = λ Hydræ, probably. From the clear description given by Al-Sufi of the starsobserved byhim, I find thathisstars are 13 = υ1; 14 = υ2; and 15 = λ Hydræ. We must, therefore, conclude that Ptolemy and Al-Sufi saw only three stars where now there are four,[443]and that κ Hydræ was not seen, or at least is not mentioned by Al-Sufi. κ is, therefore, probably variable. It was rated 4 by Tycho Brahé, Bayer, and Hevelius; it is at present about 5th magnitude. If Ptolemy did not see υ2it is probably variable also, and, indeed, it has been suspected of variable light.[444]
The small constellation of Crater, the Cup, lies north of Hydra, and south of Leo and Virgo. Al-Sufi calls ital-batija, “the Jar, or Cup.” He says the Arabians called ital-malif, “the Crib, or Manger.” According to Brown, the stars of Crater exactly form a Bakhian κάνθαρος, with its two handles rising above the two extremities of the circumference.[445]An Asia Minor legend “connected Crater with the mixing of human blood with wine in a bowl.” Crater is referred to by Ovid in the lines—
“Dixit et antiqui monumenta perennia factiAnguis, Avis, Crater sidera, juncta micunt.”
The star α Crateris was rated 4th magnitude byAl-Sufi and all other observers, and the Harvard measures make it 4·20, a satisfactory agreement. It has three companions noted by Admiral Smyth. One of these he called “intense blood colour.” This is R Crateris, now known to be variable from above the 8th magnitude to below the 9th. Sir John Herschel called it an “intense scarlet star, a curious colour.” With 3-inch refractor in the Punjab I found it “full scarlet.” It is one of an open pair, the further of the two from α. There is a third star about 9th magnitude a little south of it. Ward saw a 13th magnitude star between α and R with a 2⅞-inch (Wray) refractor. This I saw “readily” with my 3-inch. Smyth does not mention this faint star, although he used a much larger telescope.
Corvus, the Crow, is a small constellation, north of Hydra. Aratus says “the Crow form seems to peck the fold of the water snake” (Hydra). The victory which Valerius Corvinus is said to have owed to a crow has given it the name of Pomptina, because the victory took place near the Pontine marshes.[446]A quadrilateral figure is formed by its four brightest stars, γ, δ, β, and ε Corvi. This figure has sometimes been mistaken for the Southern Cross by those who are not familiar with the heavens. But the stars of the Southern Cross are much brighter.
The constellation Centaurus, the Centaur, liessouth of Hydra and Libra, and north of the Southern Cross. According to Dupuis, Centaurus represents the 3rd “labour of Hercules,” his triumph over the Centaurs.[447]The Centaurs were supposed to be a people living in the vicinity of Mount Ossa, who first rode on horses. The constellation was also called Semivir, Chiron, Phobos, Minotaurus, etc. Al-Sufi says it “is represented by the figure of an animal, of which the forepart is the upper part of a man from the head to end of the back, and its hinder part is the hinder part of a horse, from the beginning of the back to the tail. It is to the south of the Balance [Libra] turning its face towards the east, and the hinder part of the beast towards the west.”
Al-Sufi describes very clearly the four bright stars of the famous “Southern Cross.” Owing to precession these stars were some 7° further north in the tenth century than they are at present, and they could have been all seen by Al-Sufi, when on the meridian. In the time of Ptolemy and Hipparchus, they were still further north, and about 5000 years ago they were visible in the latitude of London. Dante speaks of these four stars as emblematical of the four cardinal virtues, Justice, Temperance, Fortitude, and Prudence.
Closely south-east of α and β Crucis is the dark spot in the Milky Way known as the “Coal Sack,”which forms such a conspicuous object near the Southern Cross. It was first described by Pinzon in 1499; and afterwards by Lacaille in 1755. Although to the naked eye apparently black, photographs show that it contains many faint stars, but, of course, much less numerous than in the surrounding regions. The dark effect is chiefly caused by contrast with the brilliancy of the Milky Way surrounding it.
Al-Sufi also mentions the bright stars α and β Centauri which follow the Southern Cross. He says that the distance between them “is four cubits,” that is about 9° 20′, but it is less than this now. α has a large “proper motion” of 3″·67 per annum, and was farther from β in Al-Sufi’s time than it is at present. This, however, would notwhollyaccount for the difference, and Al-Sufi’s over-estimate is probably due to the well-known effect by which the distance between two stars isapparentlyincreased when they are near the horizon. Several of Al-Sufi’s distances between southern stars are over-estimated, probably for the same reason.
The constellation Lupus, the Wolf, is south of Libra and Scorpio. It lies along the western border of the Milky Way. According to ancient writers it represents Lycaon, King of Arcadia, a contemporary of Cecrops, who is said to have sacrificed human victims, and on account of his cruelty was changed into a wolf. Another fableis that it represents a wolf sacrificed by the Centaur Chiron. According to Brown, Lupus appears on the Euphratian planisphere discovered by George Smyth in the palace of Sennacherib. Al-Sufi called ital-sabu, “the Wild Beast.” It was also calledal-fand, “the Leopard,” andal-asada, “the Lioness.”
Ara, the Altar, lies south of Scorpio. According to ancient writers it represents an altar built by Vulcan, when the gods made war against the Titans. It is called by Al-Sufial-midjman, “the Scent Box,” or “the Altar.”
The little constellation Corona Australis, the Southern Crown, lies south and west of Sagittarius, east of Scorpio, and west of Telescopium. Aratus refers to the stars in Corona Australis as—
“Other fewBefore the Archer under his forefeetLed round in circle roll without a name.”[449]
But the constellation was known by the names Caduceus, Orbiculus, Corona Sagittarii, etc. The ancient poets relate that Bacchus placed this crown in the sky in honour of his mother Semele.[450]Others say that it represents the crown conferred on Corinne of Thebes, famous as a poet.
The small constellation Piscis Australis, or theSouthern Fish, lies south of Capricornus and Aquarius. In the most ancient maps it is represented as a fish drinking the water which flows from the urn of Aquarius.
A good many constellations have been added to the heavens since the days of Al-Sufi, and notes on some of these may be of interest.
Camelopardalis.—This constellation first appears on a celestial planisphere published by Bartschius in the year 1624. It was not formed by Bartschius himself, but by the navigators of the sixteenth century. It lies south of Ursa Minor, north of Perseus and Auriga, east of Draco, and west of Cassiopeia. It contains no star brighter than the 4th magnitude.
Lynx.—This constellation is south of Camelopardalis and Ursa Major, and north of Gemini and Cancer. It was formed by Hevelius in 1660, and he called it the Lynx, because, he said, it contained only faint stars and “it was necessary to have the eyes of a lynx” to see them! Some of them were, however, observed by Ptolemy and Al-Sufi, and are mentioned by the latter under Ursa Major.
Canes Venatici, or the Hunting Dogs.—This was formed by Hevelius in 1660. It lies south of the Great Bear’s tail, north of Coma Berenices, east of Ursa Major, and west of Boötis. Its brightest stars α (12) and β (8) were observed by Al-Sufi,and included by him in the “extern” stars of Ursa Major.
Coma Berenices.—This constellation lies between Canes Venatici and Virgo. Although it was not included among the old forty-eight constellations of Ptolemy, it is referred to by Al-Sufi as the Plat, or Tress of Hair, and he included its stars Flamsteed 12, 15, and 21 in the “extern” stars of Leo. It was originally formed by the poet Callimachus in the third centuryB.C., but was not generally accepted until reformed by Hevelius. Callimachus lived at Alexandria in the reigns of Ptolemy Philadelphus and Ptolemy Euergetes, and was chief librarian of the famous library of Alexandria from aboutB.C.260 until his death inB.C.240. Eratosthenes was one of his pupils. The history of the constellation is as follows: Berenice, wife of Ptolemy Euergetes, made a vow, when her husband was leaving her on a military expedition, that if he returned in safety she would cut off her hair and consecrate it in the temple of Mars. Her husband returned, and she fulfilled her vow. But on the next day the hair had disappeared—stolen from the temple—and Conon the mathematician showed Ptolemy seven stars near the constellation of the Lion which did not belong to any constellation. These were formed into a constellation and called Berenice’s Hair. Conon is referred to by Catullus in the lines—
“Idem me ille Conon cœleste numine viditE. Berenico vertice Cæsariem.”
Coma Berenices first occurs as a distinct constellation in the catalogue contained in the Rudolphine Tables formed by Kepler (epoch 1600) from the observations of Tycho Brahé.[451]Bayer substituted a sheaf of corn, an idea derived from an ancient manuscript.
Leo Minor.—This small constellation lies between Ursa Major and Leo, and east of the Lynx. It was formed by Halley about the year 1660; but is referred to by Al-Sufi, who includes one of its stars (Fl. 41) in the “extern” stars of Leo. There are, however, several brighter stars in the group. The brightest, Fl. 46, was measured 3·92 at Harvard. The star Fl. 37 was calledpræcipua(or brightest) by Tycho Brahé, and rated 3, but as it was measured only 4·77 at Harvard it may possibly have diminished in brightness.
Sextans.—This constellation lies south of Leo, and north and east of Hydra. It was formed by Hevelius about the year 1680. According to the Harvard photometric measures its brightest star is Fl. 15 (4·50).
Monoceros, or the Unicorn, lies south of Gemini and Canis Minor, north of Canis Major and Argo, east of Orion, and west of Hydra. It appears on the planisphere of Bartschius, published in1624. According to Scaliger it is shown on an old Persian sphere. One of its stars, Fl. 22, is mentioned by Al-Sufi among the “extern” stars of Canis Major (No. 1). Another, Fl. 30, is given under Hydra (“Extern” No. 1) and Fl. 8, 13, and 15 are apparently referred to in Gemini. The star 15 Monocerotis is a little south of ξ Geminorum, and was measured 4·59 magnitude at Harvard. It was at one time supposed to be variable with a short period (about 3½ days), but this variation has not been confirmed. The spectrum is of the fifth type—with bright lines—a very rare type among naked-eye stars. It is a triple star (5, 8·8, 11·2: 2″·9, 16″·3) and should be seen with a 4-inch telescope. It has several other small companions, one of which (139°·2: 75″·7) has been suspected of variation in light. It was estimated 8½ by Main in 1863, but only 12 by Sadler in 1875. Observing it on March 28, 1889, with 3-inch refractor, I found it about one magnitude brighter than a star closely preceding, and estimated it 8 or 8½ magnitude. It is probably variable and should be watched.
Scutum Sobieski.—This is, or was, a small constellation in the southern portion of Aquila, which was formed by Hevelius in 1660 in honour of the Polish hero Sobieski. Its principal stars, which lie south-west of λ Aquilæ, were mentioned by Al-Sufi and are referred to by him under that constellation. It contains a very bright spot ofMilky Way light, which may be well seen in the month of July just below the star λ Aquilæ. Closely south of the star 6 Aquilæ is a remarkable variable star R Scuti (R.A. 18h42m·2, S. 5° 49′). It varies from 4·8 to 7·8 with an irregular period. All the light changes can be observed with a good opera-glass.
Vulpecula, the Fox.—This modern constellation lies south of Cygnus, north of Sagitta and Delphinus, east of Hercules, and west of Pegasus. It was formed by Hevelius in 1660. One of its stars, 6 Vulpeculæ, is mentioned by Al-Sufi in describing the constellation Cygnus. Closely north-west of 32 Vulpeculæ is the short-period variable T Vulpeculæ. It varies from 5·5 to 6·2 magnitude, and its period is 4·436 days. This is an interesting object, and all the changes of light can be observed with an opera-glass.
Lacerta.—This little constellation lies south of Cepheus and north of Pegasus. Its formation was first suggested by Roger and Anthelm in 1679, and it was called by them “The Sceptre and the Hand of Justice.” It was named Lacerta by Hevelius in 1690, and this name it still retains. Al-Sufi seems to refer to its stars in his description of Andromeda, but does not mention any star in particular. It brightest star Fl. 7 (α Lacertæ) is about the 4th magnitude. About one degree south-west of 7 is 5 Lacertæ, a deep orange star with a blue companion in a fine field.
There are some constellations south of the Equator which, although above Al-Sufi’s horizon when on the meridian, are not described by him, as they were formed since his time. These are as follows:—
Sculptor.—This constellation lies south of Aquarius and Cetus, and north of Phœnix. Some of its stars are referred to by Al-Sufi under Eridanus as lying within the large triangle formed by β Ceti, Fomalhaut, and α Phœnicis. The brightest star is α, about 12° south of β Ceti (4·39 magnitude Harvard). About 7° south-east of α is the red and variable star R Sculptoris; variable from 6·2 to 8·8 magnitude, with a period of about 376 days. Gould describes it as “intense scarlet.” It has a spectrum of the fourth type.
Phœnix.—This constellation lies south of Sculptor. Some of its stars are referred to by Al-Sufi, under Eridanus, as forming a boat-shaped figure. These are evidently α, κ, μ, β, ν, and γ. α is at the south-eastern angle of Al-Sufi’s triangle referred to above (under “Sculptor”). (See Proctor’s Atlas, No. 3.)
Fornax, the Furnace, lies south of Cetus, west of Eridanus, and east of Sculptor and Phœnix. It was formed by Lacaille, and is supposed to represent a chemical furnace with an alembic and receiver! Its brightest star, α Fornacis, is identical with 12 Eridani.
Cælum, the Sculptor’s Tools, is a small constellation east of Columba, and west of Eridanus. It was formed by Lacaille. The brightest stars are α and γ, which are about 4½ magnitude. α has a faint companion; and γ is a wide double star to the naked eye.
Antlia, the Air Pump, lies south of Hydra, east and north of Argo, and west of Centaurus. It was formed by Lacaille. It contains no star brighter than 4th magnitude. The brightest, α, has been variously rated from 4 to 5, and Stanley Williams thinks its variability “highly probable.”
Norma, the Rule, lies south of Scorpio. It contains no star brighter than the 4th magnitude.
Telescopium.—This modern constellation lies south of Corona Australis, and north of Pavo. Its stars α, δ, and ζ, which lie near the northern boundary of the constellation, are referred to by Al-Sufi in his description of Ara.
Microscopium.—This small constellation is south of Capricornus, and west of Piscis Australis. Its stars seem to be referred to by Al-Sufi as having been seen by Ptolemy, but he does not specify their exact positions. It contains no star brighter than 4½ magnitude.
South of Al-Sufi’s horizon are a number of constellations surrounding the south pole, which, of course, he could not see. Most of these have been formed since his time, and these will now beconsidered; beginning with that immediately surrounding the South Pole (Octans), and then following the others as nearly as possible in order of Right Ascension.
Octans.—This is the constellation surrounding the South Pole of the heavens. There is no bright star near the Pole, the nearest visible to the naked eye being σ Octantis, which is within one degree of the pole. It was estimated 5·8 at Cordoba. The brightest star in the constellation is ν Octantis (α, Proctor), which lies about 12 degrees from the pole in the direction of Indus and Microscopium. The Harvard measure is 3·74 magnitude.
Hydrus, the Water-Snake, is north of Octans in the direction of Achernar (α Eridani). The brightest star is β, which lies close to θ Octantis. The Harvard measure is 2·90. Gould says its colour is “clear yellow.” It has a large proper motion of 2″·28 per annum. Sir David Gill found a parallax of 0″·134, and this combined with the proper motion gives a velocity of 50 miles a second at right angles to the line of sight. γ Hydri is a comparatively bright star of about the 3rd magnitude, about 15½ degrees from the South Pole. It is reddish, with a spectrum of the third type.
Horologium, the Clock, is north of Hydra, and south of Eridanus. Three of its stars, α, δ, and ψ, at the extreme northern end of the constellation,seem to be referred to by Al-Sufi in his description of Eridanus, but he does not give their exact positions. Most of the stars forming this constellation were below Al-Sufi’s horizon.
Reticulum, the Net, is a small constellation to the east of Hydrus and Horologium. The brightest star of the constellation is α (3·36 Harvard, 3·3 Cordoba, and “coloured”).
Dorado, the Sword Fish, lies east of Reticulum and west of Pictor. It contains only two stars brighter than the 4th magnitude. These are α (3·47 Harvard) and β (3·81 Harvard, but suspected of variation). About 3° east of α Reticuli is the variable star R Doradus. It varies from 4·8 to 6·8, and its period is about 345 days. Gould calls it “excessively red.” It may be followed through all its fluctuations of light with an opera-glass.
Mensa, or Mons Mensa, the Table Mountain, lies between Dorado and the South Pole, and represents the Table Mountain of the Cape of Good Hope. It contains no star brighter than the 5th magnitude.
Pictor, the Painter’s Easel, lies north of Doradus, and south of Columba. It contains no very bright stars, the brightest being α (3·30 Harvard).
Volans, the Flying Fish, is north of Mensa, and south and west of Argo. Its brighter stars, with the exception of α and β, form an irregular six-sided figure. Its brightest star is β (3·65) accordingto the Harvard measures. The Cordoba estimates, however, range from 3·6 to 4·4, and Gould says its colour is “bright yellow.” Williams rated it 3·8.
Chamælion.—This small constellation lies south of Volans, and north of Mensa and Octans. None of its stars are brighter than the 4th magnitude, its brightest being α (4·08 Harvard) and γ (4·10).
Argo.—This large constellation extends much further south than Al-Sufi could follow it. The most southern star he mentions is ε Carinæ, but south of this are several bright stars. β Carinæ is 1·80 according to the Harvard measures; υ Carinæ, 3·08; θ, 3·03; ω, 3·56; and others. A little north-west of ι is the long-period variable R Carinæ (9h29m·7, S. 62° 21′, 1900). It varies from 4·5 at maximum to 10 at minimum, and the period is about 309·7 days. A little east of R Carinæ is another remarkable variable star,lCarinæ (R.A. 9h42m·5, S. 62° 3′). It varies from 3·6 to 5·0 magnitude, with a period of 35½ days from maximum to maximum. All the light changes can be observed with an opera-glass, or even with the naked eye. It was discovered at Cordoba. The spectrum is of the solar type (G).
Musca, the Bee, is a small constellation south of the Southern Cross and Centaurus. Its brightest stars are α (2·84 Harvard) and β (3·26). These two stars form a fine pair south ofα Crucis. Closely south-east of α is the short-period variable R Muscæ. It varies from 6·5 to 7·6 magnitude, and its period is about 19 hours. All its changes of light may be observed with a good opera-glass.
Apus, the Bird of Paradise, lies south-east of Musca, and north of Octans. Its brightest star is α, about the 4th magnitude. Williams calls it “deep yellow.” About 3° north-west of α, in the direction of the Southern Cross, is θ Apodis, which was found to be variable at Cordoba from 5½ to 6½. The spectrum is of the third type, which includes so many variable stars.
Triangulum Australis, the Southern Triangle, is a small constellation north of Apus, and south of Norma. A fine triangle, nearly isosceles, is formed by its three bright stars, α, β, γ, the brightest α being at the vertex. These three stars form with α Centauri an elongated cross. The stars β and γ are about 3rd magnitude. β is reddish. ε (4·11, Harvard) is also reddish, and is nearly midway between β and γ, and near the centre of the cross above referred to. α is a fine star (1·88 Harvard) and is one of the brightest stars in the sky—No. 33 in a list of 1500 highest stars given by Pickering. About 1° 40′ west of ε is the short-period variable R Trianguli Australis (R.A. 15h10m·8, S. 66° 8′) discovered at Cordoba in 1871. It varies from 6·7 to 7·4, and the period is about 3d7h·2. Although not visible to ordinaryeyesight it is given here, as it is an interesting object and all its light changes may be well seen with an opera-glass. A little south-east of β is another short-period variable, S Trianguli Australis (R.A. 15h52m·2, S. 63° 30′), which varies from 6·4 to 7·4, with a period of 6·3 days; and all its fluctuations of light may also be observed with a good opera-glass.
Circinus, the Compass, is a very small constellation lying between Triangulum and Centaurus. Its brightest star, α, is about 3½ magnitude, about 4° south of α Centauri.
Pavo, the Peacock, lies north of Octans and Apus, and south of Telescopium. Its brightest star is α, which is a fine bright star (2·12 Harvard). κ is a short-period variable. It varies from 3·8 to 5·2, and the period is about 9 days. This is an interesting object, as all the fluctations of light can be observed by the naked eye or an opera-glass. ε Pavonis was measured 4·10 at Harvard, but the Cordoba estimates vary from 3·6 to 4·2. Gould says “it is of a remarkably blue colour.”
Indus.—This constellation lies north of Octans, and south of Sagittarius, Microscopium, and Grus. One of its stars, α, is probably referred to by Al-Sufi in his description of Sagittarius; it lies nearly midway between β Sagittarii and α Gruis, and is the brightest star of the constellation. The star ε Indi (4·74 Harvard) has a remarkably largeproper motion of 4″·68 per annum. Its parallax is about 0″·28, and the proper motion indicates a velocity of about 49 miles a second at right angles to the line of sight.
Toucan.—This constellation lies north of Octans, and south of Phœnix and Grus, east of Indus, and west of Hydrus. Its brightest star is α, of about the 3rd magnitude.
There are seven “celestial rivers” alluded to by the ancient astronomers:—
1. The Fish River, which flows from the urn of Aquarius.
2. The “River of the Bird,” or the Milky Way in Cygnus.
3. The River of the Birds—2, including Aquila.
4. The River of Orion—Eridanus.
5. The River of the god Marduk—perhaps the Milky Way in Perseus.
6. The River of Serpents (Serpens, or Hydra).
7. The River of Gan-gal (The High Cloud)—probably the Milky Way as a whole.
There are four serpents represented among the constellations. These are Hydra, Hydrus, Serpens, and Draco.
According to the late Mr. Proctor the date of the building of the Great Pyramid was about 3400B.C.[452]At this time the Spring Equinox was inTaurus, and this is referred to by Virgil. But this was not so in Virgil’s time, when—on account of the precession of the equinoxes—the equinoctial point had already entered Pisces, in which constellation it still remains. At the date 3400B.C.the celestial equator ran along the whole length of the constellation Hydra, nearly through Procyon, and a little north of the bright red star Antares.
The star Fomalhaut (α Piscis Australis) is interesting as being the most southern 1st magnitude star visible in England, its meridian altitude at Greenwich being little more than eight degrees.[453]
With reference to the Greek letters given to the brighter stars by Bayer (in his Atlas published in 1603), and now generally used by astronomers, Mr. Lynn has shown that although “Bayer did uniformly designate the brightest stars in each constellation by the letter α,”[454]it is a mistake to suppose—as has often been stated in popular books on astronomy—that he added the other Greek lettersin order of brightness. That this is an error clearly appears from Bayer’s own “Explicatio” to his Atlas, and was long since pointed out by Argelander (1832), and by Dr. Gould in hisUranometria Argentina. Gould says,“For the stars of each order, the sequence of the letters in no manner represents that of their brightness, but depended upon the positions of the stars in the figure, beginning usually at the head, and following its course until all the stars of that order of magnitude were exhausted.” Mr. Lynn says, “Perhaps one of the most remarkable instances in which the lettering is seen at a glance not to follow the order of the letters is that of the three brightest stars in Aquila [Al-Sufi’s ‘three famous stars’], γ being evidently brighter than β. But there is no occasion to conjecture from this that any change of relative brightness has taken place. Bayer reckoned both of these two of the third magnitude, and appears to have arranged β before γ, according to his usual custom, simply because β is in the neck of the supposed eagle, and γ at the root of one of the wings.”[455]Another good example is found in the stars of the “Plough,” in which the stars are evidently arranged in the order of the figure and not in the order of relative brightness. In fact, Bayer is no guide at all with reference to star magnitudes. How different Al-Sufi was in this respect!
The stars Aldebaran, Regulus, Antares, and Fomalhaut were called royal stars by the ancients. The reason of this was that they lie roughly about 90° apart, that is 6 hours of Right Ascension. So, if through the north and south poles of theheavens and each of these stars we draw great circles of the sphere, these circles will divide the sphere into four nearly equal parts, and the ancients supposed that each of these stars ruled over a quarter of the sphere, an idea probably connected with astrology. As the position of Aldebaran is R.A. 4h30m, Declination North 16° 19′, and that of Antares is R.A. 16h15m, Declination South 25° 2′, these two stars lie at nearly opposite points of the celestial sphere. From this it follows that our sun seen from Aldebaran would lie not very far from Antares, and seen from Antares it would appear not far from Aldebaran.
The following may be considered as representative stars of different magnitudes. For those of first magnitude and fainter I have only given those for which all the best observers in ancient and modern times agree, and which have been confirmed by modern photometric measures. The Harvard measures are given:—
The Visible Universe
Someresearches on the distribution of stars in the sky have recently been made at the Harvard Observatory (U.S.A.). The principal results are:—(1) The number of stars on any “given area of the Milky Way is about twice as great as in an equal area of any other region.” (2) This ratio does not increase for faint stars down to the 12th magnitude. (3) “The Milky Way covers about one-third of the sky and contains about half of the stars.” (4) There are about 10,000 stars of magnitude 6·6 or brighter, 100,000 down to magnitude 8·7, one million to magnitude 11, and two millions to magnitude 11·9. It is estimated that there are about 18 millions of stars down to the 15th magnitude visible in a telescope of 15 inches aperture.[456]
According to Prof. Kapteyn’s researches on stellar distribution, he finds that going out from the earth into space, the “star density”—that is,the number of stars per unit volume of space—is fairly constant until we reach a distance of about 200 “light years.” From this point the density gradually diminishes out to a distance of 2500 “light years,” at which distance it is reduced to about one-fifth of the density in the sun’s vicinity.[457]
In a letter to the late Mr. Proctor (Knowledge, November, 1885, p. 21), Sir John Herschel suggested that our Galaxy (or stellar system) “contained within itself miniatures of itself.” This beautiful idea is probably true. In his account of the greater “Magellanic cloud,” Sir John Herschel describes one of the numerous objects it contains as follows:—