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BURNHAM'S CELESTIAL HANDBOOK
An Observer's Guide to the Universe Beyond the Solar System
By ROBERT BURNHAM JR.
Dover Publications, Inc.Copyright © 1978 Robert Burnham, Jr.
All rights reserved.
Name– The "Peacock Star", honoring the bird sacred to Juno; the constellation name is of no great antiquity, however, as it was introduced by Bayer in the early 17th century. Magnitude 1.93; spectrum B3 IV; position 20217s5654. The computed distance is about 310 light years, and the actual luminosity about 1200 times the Sun. Alpha Pavonis shows an annual proper motion of 0.09"; the radial velocity is 1.2 mile per second in recession. Spectroscopic studies show that the star is a close binary with a period of 11.753 days.
Magnitude 3.42; spectrum A5 IV; position 20405s6623. The distance is about 160 light years and the actual luminosity about 90 times the Sun. The annual proper motion is 0.05"; the radial velocity is 6 miles per second in recession.
Globular star cluster. Position 19064s6004, about 10° WSW from Alpha Pavonis. One of the finest of the globular clusters, though almost unknown to observers in North America or Europe owing to its far southern location. It was probably first observed by J. Dunlop in 1828, and with a total integrated magnitude of 7.2 ranks as the 7th brightest globular in the sky. In apparent size it possibly holds third place, only Omega Centauri and 47 Tucanae appear to exceed it. The total diameter is about 42' on the best photographs, though the visual size is about 15' or 16' in most telescopes. "One of the gems of the sky" states E.J. Hartung. "On a clear dark night this is a most lovely object......a moderately condensed type of globular cluster, the central region about 3' wide and the unusually bright outliers extending over 15', involving an elegant pair (7.7+9.3, 3[??]0, 238°). Many of the brighter stars of the cluster are in curved and looped arms, and look distinctly rreddish.. The cluster is among, the nearer globulars with a computed distance of about 20,000 light years and a true luminosity of close to 100,000 suns. NGC 6752 contains only two known variable stars, one of which has been known since 1897. The total integrated spectral type is about F6; the radial velocity is a very moderate 23 miles per second in approach.CHAPTER 2
Name– MARKAB or MARCHAB, from the Arabian word for Saddle, though the term might also refer to a ship. Other Arabic names were Matn al Faras, the Horse's Shoulder, and Yed Alpheras, the Horse's Forearm or Hand. Magnitude 2.50; spectrum B9 or A0 III; position 23023n1456. The star marks the southwest corner of the "Great Square of Pegasus", the huge squarish figure about 18° · 14° that outlines the body of the Horse. Alpha Pegasi lies at a distance of about 110 light years, and has about 95 times the solar luminosity (absolute magnitude about -0.1). The annual proper motion is 0.07"; the radial velocity is 2.2 miles per second in approach, with slight but definite variations. The star lies in a rather blank part of the sky, lacking in faint stars; the interesting spiral galaxy NGC 7479, however, will be found about 2.9° almost directly south. (See photograph on page 1392)
Pegasus is, of course, the famed Flying Horse of Greek mythology, one of the most curious, but also one of the loveliest concepts created by the ancient myth–makers of the Greek world. In legend he was born from the blood of the Medusa, when that monster had been slain by Perseus, and his name, it is thought, comes from the Greek [TEXT NOT REPRODUCIBLE IN ASCII] or "Pegae", the "Springs of the Ocean" at the place of his birth. The word [TEXT NOT REPRODUCIBLE IN ASCII] or "strong" has also been suggested as a possible source of the name. After his creation, the Winged Horse made his first landing on the rocky heights above Corinth, where the blow of his hoof caused the famous spring of Peirene to gush forth; the spot was sacred to the Corinthians, and Pegasus was held in special reverence by the inhabitants of the city. A similar tradition credited Pegasus with having produced the Fount of Hippocrene on Mt. Helicon. Pegasus appears on coins of Corinth as early as 550 BC, where he is shown in a curiously archaic style (Fig.1); some of the later issues, in high classic style, are among the finest of coin creations of the ancient world and are eagerly sought by collectors:
The coin shown in Figure 2 was struck in the early 4th Century BC at Ambracia, while the specimen shown in Fig.4 dates to about 320 BC and was minted at Lokroi in Bruttium. The style was adopted by many cities of the Greek world; the obverse of virtually all of these coins shows a classic head of Athena, wearing the traditional Corinthian helmet. Pegasus also is featured on some of the large bronze coins of Carthage, probably minted in Sicily during the final years of the city's existence, before its total destruction by the Romans in 146 BC. (Fig.3)
Pegasus was tamed by Athena or Minerva according to Greek legend, and given to the Muses, in whose service he became the symbol of poetic inspiration; in another tradition he carried the thunder and lightning for Zeus. In another classic tale he became the steed of the Greek hero Bellerophon, Prince of Corinth, and slayer of the fearsome Chimaera, a most unlikely combination of lion, serpent, and goat. Bellerophon tamed the fabulous Flying Horse with the aid of Athena, after spending a night in prayer in her temple, and had many other fabulous adventures with the great horse. Eventually, however, Bellerophon became so bold as to attempt to fly to Olympus itself; the wiser Pegasus refused to attempt the flight and threw his rider to Earth. The tradition which connects Pegasus with the hero Perseus is of more modern origin, and is not supported by the ancient myths. The famous painting by Rubens, which depicts Pegasus present at the Rescue of Andromeda, is a part of this modem mythos; Shakespeare also refers in Troilus and Cressida to "Perseus' horse", evidently an allusion to Pegasus. In Greek writings Pegasus is often called simply "The Horse" or occasionally "The Divine Horse"; the Romans called it Equus Gorgoneus or Equus Ales, the "Winged Horse"; another popular title was Alatus or "The Winged One" which appears in the Alfonsine Tables. In other Latin manuscripts it is called Equus Medusaeus which requires no translation. In the 1551 edition of Ptolemy's Almagest it is given as Equus Pegasus.
According to R.H.Allen, the constellation is identified as the Horse of Nimrod bby ancient Jewish writers; the identification with the Archangel Gabriel is relatively modem, and has been attributed to Julius Schiller.
In the sky Pegasus appears turned over on his back with his body outlined by the Great Square (Alpha, Beta, Gamma, and the Alpha of Andromeda). His front legs are marked by Eta and Iota Pegasi, and his head by Epsilon; the great wings are not clearly indicated, but would lie more or less at the position of the "Circlet of Pisces", some 10° below the southern edge of the Great Square.
Name– SCHEAT, from the Arabic Al Sa'id or Sa'd, the "Upper Part of the Arm" or possibly "The Foreleg". Riccioli has it labeled Sdheat Alpheraz while Bayer has Seat Alpheras. Schickard's title appears to be very corrupted Arabic: Saidol–Pharazi. Beta Pegasi is magnitude 2.50 (variable); spectrum M2 II or III; the position is 23014n2749. The star marks the northwest corner of the Great Square of Pegasus.
Scheat is an irregular red variable star, similar in behavior to Betelgeuse, but much less extreme in size and luminosity. It varies from magnitude 2.1 to about 3.0 in an irregular period. The star was one of the first to be measured with the beam interferometer on the 100–inch reflector at Mt. Wilson; the apparent angular size was found to be about 0.021". At the computed distance this corresponds to about 145 times the diameter of the Sun. Beta Pegasi, like Betelgeuse, varies somewhat in size during the course of the light cycle; the maximum diameter may be about 160 times the diameter of our Sun. The true luminosity varies from about 240 suns up to about 500. If Beta Pegasi should replace our sun, the star would not quite fill the Earth's orbit. E.J. Hartung (1968) comments on the fine appearance of the spectrum of this star, "with broad dark bands in red and orange, and a series of narrower bands in green, blue and violet."
The computed distance is about 210 light years, the surface temperature about 3100°K, the mass about 5 solar masses, and the average density about one millionth that of the Sun. The star shows an annual proper motion of 0.23" in PA 54°; the radial velocity is 5 miles per second in recession.
Two faint field stars are listed in the ADS catalogue as companions to Beta Pegasi, but these are optical attendants only, and do not share the proper motion of the bright star:
Mag 11 at 108.5" in PA 211° (1924)
9 253.1" 98° "
The AB separation is slowly increasing from about 80" in 1828, while the AC distance is diminishing; both changes are the result of the proper motion of the bright star.
Name– ALGENIB, probably from the Arabic Al Janb, "The Side", though some authorities derive it from Al Jonah, "The Wing". Magnitude 2.84, spectrum B2 IV, position 00107n1454. The star marks the southeast corner of the Great Square of Pegasus. Gamma Pegasi is a giant star, at a computed distance of about 570 light years, and with an actual luminosity of about 1900 times that of the Sun (absolute magnitude -3.4.) The annual proper motion is about 0.01"; the radial velocity is 2.5 miles per second in recession.
One of the Beta Canis Majoris variables, the star has an unusually short period of 0.1517495 day, or about 3 hours and 38 minutes. As in all the stars of this type, the light variations are very slight, only a few hundredths of a magnitude.
The variable radial velocity of this star was first detected by K.Bums at the Lick Observatory in 1911. Owing possibly to the small amplitude of the variations, no further studies of the star were made until 1952 when D.H. McNamara and A.D. Williams at the University of California found the period to be remarkably short, only 3.63 hours. At the time this was the shortest period known for any Beta Canis star, but the star Theta Ophiuchi has since been found to have a period of 3h 22m. Light curves for Gamma Pegasi were measured in different colors by M. Jerzykiewicz in 1970, and it was found that the B magnitude shows slight but regular variations of less than 0.01 magnitude in a period of about 44 minutes, close to 1/5 the main period of the star. The V–B color index becomes smallest around the time of maximum light. Stars of this type are believed to be rather massive, young stars which are beginning to evolve away from the main sequence. (Refer also to Beta Canis Majoris, page 435)
The interesting eclipsing variable U Pegasi lies about 3.8° to the west and slightly north.(See page 1378)
Name– ENIF, from Al Anf, "The Nose". Medieval Arabian charts sometimes label it Fum al Faras or "The Horse's Mouth". Magnitude 2.31, spectrum K2 Ib, position 21417n0939. The star is at a computed distance of about 780 light years, giving an actual luminosity of about 5800 times that of the Sun, and an absolute magnitude of -4.6. The annual proper motion is 0.025"; the radial velocity is slightly under 3 miles per second in recession. From the position on the H–R diagram, the estimated mass of the star is close to 10 solar masses.
Two faint stars in the field are not true physical companions to Epsilon; the further one, at 143", has been mentioned in many observing books owing to the statement by Herschel that the star exhibits a curious optical phenomenon: "the apparent pendulum–like oscillation of a small star in the same vertical as the large one, when the telescope is swung from side to side.." Herschel suggested that the seemingly larger arc traversed by the small star was due to the greater time required for its faint light to affect the eye, so that "the reversal of motion is first perceived in the larger object".
The fine globular star cluster M15 may be found in binoculars by sweeping an area about 4° to the northwest. (Refer to page 1383)
Name– HOMAM, probably from the Arabic phrase Sa'd al Humam, the "Lucky Star of the Hero", though Thomas Hyde derived it from Al Hammam, which seems to mean "The Whispering One". According to R.H. Allen, the names Sa'd al Na'amah, "The Lucky Star of the Ostriches" and Na'ir Sa'd al Bahaim, "The Bright Fortunate One of the Two Beasts" were also in use among the Arabs. The Chinese, for some unknown reason, connected the star with thunder. Zeta Pegasi is magnitude 3.46, spectrum B8 V, position 22390n1034. The computed distance is about 210 light years, the actual luminosity about 145 times the sun, the annual proper motion is 0.08", and the radial velocity about 4 miles per second in recession.
The 11th magnitude companion at 62" was first noted by S.W. Burnham in 1879, but appears to have no real connection with the primary. The distance between the two stars is slowly decreasing from the proper motion of Zeta itself.
Name– MATAR, from the Arabic Al Sa'd al Matar, "The Fortunate Rain". Magnitude 2.96, spectrum G8 II + F?, Position 22407n2958. Eta Pegasi is some 360 light years distant; the actual luminosity is about 630 times that of the Sun (absolute magnitude -2.2). The star shows an annual proper motion of 0.03"; the radial velocity is 2.5 miles per second in recession.
W.W. Campbell at Lick Observatory in 1898 found the star to be a spectroscopic binary with a period of 818 days and an eccentricity of about 0.155. The primary star is close to 1 AU from the center of gravity of the system and the spectroscopic companion appears to be an F–star of uncertain class.
A visual companion at 91" is itself a very close pair of about 0.2", but probably does not form a true physical system with the bright star. The faint pair was first resolved by S.W. Burnham with the 36–inch refractor at Lick in 1889, and has shown no definite change in PA or separation since that time.
Magnitude 4.27; Spectrum F5 IV, Position 21424n2525. The parallactic distance is close to 100 light years, giving a total luminosity of about 16 suns. The annual proper motion is 0.033"; the radial velocity is about 5 miles per second in approach.
The 11th magnitude companion at about 14" has been known since 1776 when it was recorded by William Herschel; the PA has been decreasing slowly and the separation has increased about 2" in the last century. The observed change can be accounted for by the known proper motion of the primary; thus it appears that the two stars form an optical pair only, and are not physically associated.
Kappa itself is a very close binary in rapid motion, discovered by S.W. Burnham in August 1880. Burnham wrote in 1891: "The extreme difficulty of measuring so close a pair seems to have deterred other observers, with a single exception, from doing anything with it.... Since I have been at Mt. Hamilton I have measured the close pair each year with the 36–inch refractor. During the measures of the past year it was extremely difficult, and was a severe test of the power of the great telescope with the very best atmospheric conditions."
T. Lewis, at the Royal Observatory at Greenwich, in a paper written in November 1894, called attention to the fact that the star was the most rapid binary then known, and stated that Burnham's note "naturally induced an inspection with the 28–inch refractor of the Royal Observatory, Greenwich, which showed them distinctly separated with a power of 1030, and our measures appear to confirm the remarkably short period".
Modem measurements give the period as 11.53 years; periastron was in late 1955, and the separation reaches about 0.3? at maximum, as in 1964. Individual magnitudes are 4.8 and 5.2; spectral types are F5 (subgiant) and about K0. From the computed orbit the masses of the two stars are 1.6 and 1.5; the absolute magnitudes are +2.3 and +2.7. Orbital elements, according to W.J. Luyten, are: Semi-major axis= 0.22? or about 7.5 AU; Eccentricity= 0.30; Inclination= 109°; motion retrograde with periastron= 1909.86. In addition, the brighter star is a spectroscopic binary with a period of 5.9715 days.
Magnitude 3.50; Spectrum G8 III; Position 22476n2420, about 4.5° SW from Beta Pegasi. The parallactic distance is about 100 light years, which gives the star an actual luminosity of about 30 suns. The annual proper motion is 0.15"; the radial velocity is about 8.5 miles per second in recession.
Excerpted from BURNHAM'S CELESTIAL HANDBOOK by ROBERT BURNHAM JR.. Copyright © 1978 Robert Burnham, Jr.. Excerpted by permission of Dover Publications, Inc..
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