作者：Olcott, William Tyler
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A Field Book of the Stars试读：
INTRODUCTION.
Considering the ease with which a knowledge of the constellations can be acquired, it seems a remarkable fact that so few are conversant with these time-honored configurations of the heavens．Aside from a knowledge of "the Dipper" and "the Pleiades," the constellations to the vast majority, are utterly unknown.
To facilitate and popularize if possible this fascinating recreation of star-gazing the author has designed this field-book．It is limited in scope solely to that purpose, and all matter of a technical or theoretical nature has been omitted.
The endeavor has been to include in these pages only such matter as the reader can observe with the naked eye, or an opera-glass．Simplicity and brevity have been aimed at, the main idea being that whatever is bulky or verbose is a hindrance rather than a help when actually engaged in the observation of the heavens.
The constellations embraced in this manual are only those visible from the average latitude of the New England and Middle States, and owe their place in the particular season in which they are found to the fact that in that season they are favorably situated for observation.
With this brief explanatory note of the purpose and design of the book, the author proceeds to outline the scheme of study.
SCHEME OF STUDY.
The table of contents shows the scheme of study to be pursued, and to facilitate the work it is desirable that the student follow the therein circumscribed order.
A knowledge on the part of the reader of Ursa Major, or "the Dipper" as it is commonly called, and "the Pleiades," the well-known group in Taurus, is presupposed by the author.
With this knowledge as a basis, the student is enabled in any season to take up the study of the constellations．By following out the order dictated, he will in a few nights of observation be enabled to identify the various configurations making up the several constellations that are set apart for study in that particular season.
A large plate, showing the appearance of the heavens at a designated time on the first night of the quarter, is inserted before each season's work．This should be consulted by the student before he makes an observation, in order that he may obtain a comprehensive idea of the relative position of the constellations, and also know in what part of the heavens to locate the constellation which he wishes to identify.
A knowledge of one constellation enables the student to determine the position of the next in order．In this work, the identification of each constellation depends on a knowledge of what precedes, always bearing in mind the fact that each season starts as a new and distinct part to be taken by itself, and has no bearing on that which comes before.
THE DIAGRAMS.
The diagrams, it will be observed, are grouped under the seasons, and they indicate the positions of the constellations as they appear at 9 o'clock p.m．in mid-season.
To facilitate finding and observing the constellations, the student should face in the direction indicated in the text．This applies to all constellations excepting those near the zenith.
The four large plates are so arranged that the observer is supposed to be looking at the southern skies．By turning the plate about from left to right, the eastern, northern, and western skies are shown successively.
On many of the diagrams the position of nebulæ is indicated．These are designated by the initial letter of the astronomer who catalogued them, preceded by his catalogue number, as for instance 8 M．signifies nebula number 8 in Messier's catalogue.
The magnitudes assigned to the stars in the diagrams are derived from the Harvard Photometry．When a star is midway between two 2magnitudes the numeral is underlined, thus , indicates a star of magnitude 2.5.
If a star's magnitude is between 1 and 1.5 it is regarded as a first-magnitude star．If it lies between 1.5 and 2 it is designated second magnitude.
THE CONSTELLATIONS OF SPRING.
Map showing the principal stars visible from Lat.40° N．at 9 o'clock April 1st.URSA MAJOR (er´sa mā´-jor)—THE GREAT BEAR．(Face North.)Location.—Ursa Major is probably the best known of the constellations, and in this work I presuppose that the reader is familiar with its position in the heavens．It is one of the most noted and conspicuous constellations in the northern hemisphere, and is readily and unmistakably distinguished from all others by means of a remarkable cluster of seven bright stars in the northern heavens, forming what is familiarly termed "The Dipper."
The stars α and β are called the pointers, because they always point toward the Pole Star, 28¾° distant from α.
Alioth is very nearly opposite Shedir in Cassiopeia, and at an equal distance from the Pole．The same can be said of Megres, in Ursa Major, and Caph, in Cassiopeia.
The star ο is at the tip of the Bear's nose．A clearly defined semicircle begins at ο and ends in the pair ι and κ at the extremity of the Bear's right fore paw．This group of stars resembles a sickle．Note little Alcor close to Mizar．This star was used by the Arabs as a test of good eyesight.
Mizar and Alcor are known as the horse and his rider.
This plate shows the Bear lying on his back, his feet projected up the sky; three conspicuous pairs of stars represent three of his four feet.
The Chaldean shepherds and the Iroquois Indians gave to this constellation the same name．The Egyptians called it "The Thigh."
α and η are moving through space in a contrary direction to the remaining five stars in "The Dipper."URSA MAJORURSA MINOR (er´-sa mi´-nor)—THE LITTLE BEAR．(Face North.)
Location.—The two pointer stars in Ursa Major indicate the position of Polaris, the North Star, which represents the tip of the tail of the Little Bear, and the end of the handle of the "Little Dipper." In all ages of the world, Ursa Minor has been more universally observed and more carefully noticed than any other constellation, on account of the importance of the North Star.
Polaris is a little more than 1¼° from the true pole．Its light takes fifty years to reach us.
A line joining β Cassiopeiæ, and Megres, in Ursa Major, will pass through Polaris.
At the distance of the nearest fixed star our sun would shine as a star no brighter than Polaris which is presumably about the sun's size.
Polaris revolves around the true pole once in twenty-four hours in a little circle 2½° in diameter．Within this circle two hundred stars have been photographed.
The North Star is always elevated as many degrees above the horizon as the observer is north of the equator.
Compare the light of the four stars forming the bowl of the "Little Dipper," as they are each of a different magnitude．A standard first-magnitude star is 2½ times brighter than a standard second magnitude star, etc.URSA MINORGEMINI (jem´-i-ni)—THE TWINS．(Face West.)
Location.—A line drawn from β to κ Ursæ Majoris and prolonged an equal distance ends near Castor, in Gemini．Gemini is characterized by two nearly parallel rows of stars．The northern row if extended would reach Taurus, the southern one Orion．Note the fine cluster 35 M．Herschel discovered Uranus in 1781 a short distance southwest of it．Two wonderful streams of little stars run parallel northwest on each side of the cluster．Where the ecliptic crosses the solstitial colure is the spot where the sun appears to be when it is farthest north of the equator, June 21st．Castor is a fine double for a telescope, and Pollux has three little attendant stars．An isoceles triangle is formed by Castor, Aldebaran in Taurus, and Capella in Auriga．There is a record of an occultation in Gemini noted about the middle of the fourth century b.c.
The Arabs saw in this group of stars two peacocks, the Egyptians two sprouting plants, and the Hindus twin deities, while in the Buddhist zodiac they represented a woman holding a golden cord．Since classic times, however, the figure has always been that of human twins.
At the point indicated near θ a new star was discovered by Enebo in March, 1912．It attained a maximum of about magnitude 3.5 and has at this writing waned to the eleventh magnitude.GEMINIAURIGA (â-ri´-ga)—THE CHARIOTEER．(Face Northwest.)
Location.—A line drawn from δ to α Ursæ Majoris, and prolonged about 45°, ends near the bright Capella, in Auriga, a star of the first magnitude, and one of the most brilliant in the heavens．It is unmistakable, having no rival in brightness near it．Auriga is a beautiful and conspicuous constellation．It is characterized by a clearly defined pentagon．Note the three fourth-magnitude stars near Capella known as "The Kids." The star β is common to Auriga and Taurus, being the former's right foot and the latter's northern horn．The field within the pentagon is particularly rich in clusters．Capella forms a rude square with Polaris, ε Cassiopeiæ, and ο Ursæ Majoris, and forms an equilateral triangle with Betelgeuze in Orion, and the Pleiades in Taurus.
A line from θ to α Aurigæ prolonged about 20° ends near α Persei.
Capella is visible at some hour of every clear night throughout the year．Of the first-magnitude stars it is nearest to the Pole, and it rises almost exactly in the northeast.
To the Arabs Capella was "The Driver," because it seemed to rise earlier than the other stars and so apparently watched over them, or still more practically as "The Singer" who rode before the procession cheering on the camels, which last were represented by the Pleiades.AURIGACANCER (kan´-ser)—THE CRAB．(Face West.)
Location.—Cancer lies between Gemini and Leo．A line drawn from Nath in Auriga to Pollux in Gemini, and prolonged about 15°, ends in Præsepe, the Manger, the great star cluster in Cancer, which is also called "The Bee Hive." It contains 300 stars．The stars γ and δ are called the Aselli—the ass's colts feeding from the silver manger.
The star β lies about 10° northeast of Procyon．Acubens, α lies on the same line the same distance beyond β．These two stars form the tips of the inverted "Y" which distinguishes Cancer.
An imaginary line from Capella through Pollux will point out Acubens．Close to it are two faint stars．The Bee Hive lies within an irregular square formed by γ, δ, η, and θ, and looks like a nebula to the naked eye.
In June, 1895, all the planets except Neptune were in this quarter of the heavens, and Halley's comet was in this constellation on its first appearance in 1531.
The dimness of γ and δ is an infallible precursor of rain, and if the Bee Hive is not visible in a clear sky, it is a presage of a violent storm.CANCERHYDRA (hi´-dra)—THE SEA-SERPENT．(Face South and Southwest.)
Location.—The head of Hydra, a striking and beautiful arrangement of stars, lies just below the Bee Hive, in Cancer, 6° south of Acubens in that constellation, and forms a rhomboidal figure of five stars.
Hydra is about 100° in length and reaches almost from Canis Minor to Libra．Its stars are all faint except Alphard, or the Hydra's heart, a second-magnitude star remarkable for its lonely situation, southwest of Regulus, in Leo．A line drawn from γ Leonis through Regulus points it out．It is of a rich orange tint．Castor and Pollux, in Gemini, point southeast to it.
The constellations Crater, the Cup, and Corvus, the Crow, both stand on the coils of Hydra, south of Denebola, the bright star in the tail of the Lion.
Hydra is supposed to be the snake shown on a uranographic stone from the Euphrates, 1200 b.c.
The little asterism Sextans, the Sextant, lies in the region between Regulus and Alphard．It contains no stars brighter than the fourth magnitude.HYDRALEO (le´o)—THE LION．(Face South.)
Location.—A line drawn from Pollux, in Gemini, to γ in Cancer, and prolonged about 12°, strikes Regulus, the brilliant star in the heart of the Lion．Regulus lies about 9° east of Acubens, in Cancer, and about 12° northeast of Alphard, in the heart of Hydra.
Leo is one of the most beautiful constellations in the zodiac．It lies south of the Great Bear, and its principal stars are arranged in the form of a sickle which nearly outlines the Lion's head．This group is so striking as to be unmistakable．Regulus is in the handle of the sickle．It is one of the stars from which longitude is reckoned, lies almost exactly on the ecliptic, and is visible for eight months in the year.
Denebola, the bright star in the Lion's tail, lies 25° east of Regulus, and about 35° west of Arcturus, in Boötes．It is the same distance northwest of Spica, in Virgo, and forms with Spica and Arcturus a large equilateral triangle.
ζ is double, and has three faint companion stars.
ε has two seventh-magnitude companion stars, forming a beautiful little triangle.
Regulus is white in color, γ yellow, π red.
γ is a beautiful colored telescopic double star and has a companion visible in an opera-glass.
The figure of Leo very much as we now have it appears in all the Indian and Egyptian zodiacs.LEO & THE SICKLECOMA BERENICES (kō´-ma ber-e-ni´-sez)—BERENICE'S HAIR.
Location.—A line drawn from Regulus to Zosma, in Leo, and prolonged an equal distance, strikes this fine cluster, which is 18° northeast of Zosma, δ Leonis.
The group lies well within a triangle formed by Denebola, Arcturus, in Boötes, and Cor Caroli, in Canes Venatici, which triangle is the upper half of the Diamond of Virgo.
Twenty or thirty stars in this group can be counted with an opera-glass, and the group can be easily distinguished with the naked eye, when the moon is not visible.
The first half of the month of April can be called the most brilliant sidereal period of the year．At this time eleven first-magnitude stars are visible in this latitude at 9 p.m．From east to west they are: Vega, Arcturus, Spica, Regulus, Pollux, Procyon, Sirius, Capella, Aldebaran, Betelgeuze, and Rigel, truly a glorious company, an incomparable sight.COMA BERENICESCANIS MINOR (kā´-nis mī´-nor)—THE LESSER DOG．(Face West.)
Location.—Procyon, the Little Dog Star, lies about 23° south of Pollux, in Gemini．A line drawn from Nath, in Auriga, to Alhena, in Gemini, and prolonged about 18°, reaches Procyon.
Procyon is equidistant from Betelgeuze in Orion, and Sirius in Canis Major, and forms with them an equilateral triangle．It forms a large right-angled triangle with Pollux and Betelgeuze.
The light from Procyon is golden yellow．Four degrees northwest of it is the third-magnitude star Gomeisa．The glass shows two small stars forming a right-angled triangle with it.
Procyon was distinctly mentioned by Ptolemy．It rises in this latitude a little north of east about half an hour before Sirius, the Dog Star, hence it was called Procyon from two Greek words which signify "before the dog."
Procyon is one of our nearest neighbors in space, at a distance of ten light years, and is attended by a very faint companion which is only visible in the largest telescopes.CANIS MINORCORVUS (kôr´-vus)—THE CROW．(Face South.)
Location.—A line drawn from the Bee Hive, in Cancer, through Regulus, in Leo, and prolonged about 40°, ends near the conspicuous quadrilateral which distinguishes Corvus．The brightest star in this region of the sky is Spica, in Virgo．It lies about 10° northeast of Algorab.
ζ is a double star for an opera-glass．A faint pair of stars lie close below and to the west of β．The Crow is represented as standing on, and pecking at, the coils of Hydra．The star Al Chiba is in the Crow's bill.
Corvus was known as the Raven in Chaucer's time.
δ is an interesting telescopic double.
A line drawn from γ to β Corvi and prolonged twice its length locates the third-magnitude star ι Centauri in the right shoulder of the Centaur．The brightest stars in this constellation are not visible in this latitude.CORVUSCRATER (krā´-ter)—THE CUP．(Face South.)
Location.—Crater is situated 15° west of Corvus, and due south of θ Leonis．It is easily distinguished by reason of a beautiful and very striking semicircle of six stars of the fourth magnitude, forming the bowl of the cup.
The constellation resembles a goblet with its base resting on the coils of Hydra.
The star Alkes is common to Hydra and Crater, and may be seen 24° southeast of Alphard in the heart of Hydra．It is distinguished by its forming an equilateral triangle with α and γ, stars of the same magnitude 6° south and east of it.
Corvus and Crater are to be seen half-way up the southern sky during the early evenings in spring.
δ is now the lucida.
Crater is situated at about the centre of Hydra and is on the meridian, April 26th．Owing to its many faint stars it is best seen on a clear moonless night.
The zodiacal light is well worth observing at this season of the year．It is to be seen in the western sky shortly after sundown, and is most intense during the evenings of March.CRATERMETEORIC SHOWERS.APRIL TO JULY.
The Abbreviations under Characteristics are as follows:
THE CONSTELLATIONS OF SUMMER.
Maps showing the principal stars visible from Lat.40° N．at 9 o'clock, July first.DRACO (drā´-ko)—THE DRAGON．(Face North.)Location.—About 10° from α Ursæ Majoris—from α to δ is 10°—slightly south of, that is above, the line from α to Polaris, is Giansar, λ in the tip of the Dragon's tail．Above λ, and almost in line with it, are two more stars in Draco, which form with two stars in Ursa Major a quadrilateral．(See diagram.) Draco now curves sharply eastward, coiling about the Little Bear as shown, then turns abruptly southerly, ending in a characteristic and clearly defined group of four stars, forming an irregular square, representing the Dragon's head．This group is almost overhead in the early evening in summer．The star in the heel of Hercules lies just south of the Dragon's head．The brilliant Vega will be seen about overhead, 12° southwest of the Dragon's head．Eltanin, one of the Dragon's eyes, is noted for its connection with the discovery of the law of aberration of light．It is of an orange hue, while the star β, near it, is white．Note Thuban, once the Pole Star, at one corner of a quadrilateral that Draco forms with Ursa Major.
Thuban could be seen by day or night from the bottom of the central passage of several of the Pyramids in Egypt.
The rising of Eltanin was visible about thirty-five hundred years b.c．through the central passages of the temples of Hathor at Denderah．The Egyptians called Draco "The Hippopotamus."
Vega and the four stars in the Dragon's head offer an opportunity to compare the first five stellar magnitudes with which all should be familiar.DRACOLYRA (lī´-ra)—THE LYRE.
Location.—Lyra may be easily distinguished because of the brilliant Vega, its brightest star, which is situated about 12° southwest of the Dragon's head．It is unmistakable, as it is the brightest star in this region of the heavens, and the third brightest in this latitude．In July and August Vega is close to the zenith in the early evening.
The six bright stars in Lyra form an equilateral triangle on one corner of a rhomboid．A very characteristic figure.
ε is a pretty double for an opera-glass, and a 3" glass reveals the duplicity of each star of this pair．ε is therefore a double double.
ζ is a double for a good glass.
β is a variable, changing from magnitude 3.4 to 4.4 in twelve days．At its brightest it is about equal to its near neighbor γ Lyræ.
The noted ring nebula lies between β and γ．A 3" glass reveals it but a powerful telescope is required to render its details visible.
If the distance from the earth to the sun equalled one inch, the distance from the earth to Vega would be 158 miles.
Vega was the first star to be photographed, in 1850．It is visible at some hour every clear night, and has been called the arc-light of the sky．Its light has the bluish-white hue that suggests "a diamond in the sky."
The spectroscope reveals that Vega is a star probably only in its infancy, as hydrogen is its predominating element.LYRACYGNUS (sig´-nus)—THE SWAN, OR THE NORTHERN CROSS.
Location.—Deneb, the brightest star in Cygnus, is at the top of the cross, and a little over 20° east of Vega．It forms a triangle with Vega and Altair in Aquila—Altair being at the apex, about 35° from Deneb and Vega.
β Cygni is at the base of the cross, and a line drawn from Vega to Altair nearly touches it．It is a beautiful colored double for a small telescope.
Note "61," one of the nearest stars to us．It was the first star whose distance was measured (by Bessel in 1838)．It is a double star and 10.4 light years distant.
The cross is nearly perfect and easily traced out．It lies almost wholly in the Milky Way.
Note "The Coal Sack," one of the dark gap in the Milky Way.
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