« НазадПродовжити »
first minimum of this star in the year 1844 occurred on Jan. 3. at 4h 14m Greenwich mean time. *
(822). The star 8 in the constellation Cepheus is also subject to periodical variations, which, from the epoch of its first observation by Goodricke in 1784 to the present time, have been continued with perfect regularity. Its period from minimum to minimum is 5d gh 47m 399.5, the first or epochal minimum for 1849 falling on Jan. 2. 3h 13m 378 M. T. at Greenwich. The extent of its variation is from the fifth to between the third and fourth magnitudes. Its increase is more rapid than its diminution, the interval between the minimum and maximum of its light being only 1d 14", while that from the maximum to the minimum is 3d 19h.
(823.) The periodical star ß Lyræ, discovered by Goodricke also in 1784, has a period which has been usually stated at from 6à gh to 6d 115, and there is no doubt that in about this interval of time its light undergoes a remarkable diminution and recovery. The more accurate observations of M. Argelander however have led him to conclude t the true period to be 124 21h 53m 109, and that in this period a double maximum and minimum takes place, the two maxima being nearly equal and both about the 3.4 magnitude, but the minima considerably unequal, viz. 4.3 and 4.5m. In addition to this curious subdivision of the whole interval of change into two semi-periods, we are presented in the case of this star with another instance of slow alteration of period, which has all the appearance of being itself periodical. From the epoch of its discovery in 1784 to the year 1840 the period was continually lengthening, but more and more slowly, till at the last-mentioned epoch it ceased to increase, and has since been slowly on the decrease. As an epoch for the least or absolute minimum of this star, M. Argelander's calculations enable us to assign 1846 January 3d on gm 53s G. M. T.
(824.) Another periodical star whose changes have been
• Ast. Nach. No. 472.
† Astron. Nachr. No. 624. See also the valuable papers by this excellent astronomer in A. N. Nos. 417, 455, &c.
carefully observed is » Aquilæ or Antinoi, first pointed out by Pigott in 1784 (a year fertile in such discoveries) as belonging to that class. Its period is 7d 4h 13m 53*, the first minimum for 1849 occurring on Jan. 2. at 19h 22m 558 G.M.T. It occupies fifty-seven hours in its increase from 5m to 4:3m, and 115 hours in its decrease.
(825.) These are all the variable stars which have been observed with sufficient care and for a sufficient length of time to enable us to speak with precision as to their periods, epochs, and phases of brightness. But the number of those whose period is approximately or roughly known is considerable, and of those whose change is certain, though its period and limits are as yet unknown, still more so. The following table includes the principal among them, though each year adds to their number:
N. B. In the above list the letters B. A. C. indicate the catalogue of the British Association, B. the catalogue of Bode. Numbers before the name of the constellation (as 34 Cygni) denote Flamsteed's stars. Since this table was drawn up, four additional stars, variable from the 8th or 9th magnitude to 0, have been communicated to us by Mr. Hind, whose places are as follows: (1.) R. A. 1h 38m 249; N. P. D. 81° 9' 59''; (2.) 4h 50m 425, 82° 6' 36" (1846); (3.) gb 43m 8', 86° 11' (1800); (4.) 22h 12m 98, 82° 59' 24" (1800). Mr. Hind remarks that about several variable stars some degree of haziness is perceptible at their minimum. Have they clouds revolving round them as planetary or cometary attendants? He also draws attention to the fact that the red colour predominates among variable stars generally. The double star, No 2718 of Struve's Catalogue, R. A. 20h 34m, P. D. 77° 54', is stated by the author to be variable. Captain Smyth (Celestial Cycle, i. 274.) mentions also 3 Leonis and 18 Leonis as variable, the former from 6m to 0, P=78 days, the latter from 5 to 10m, P= 3114 23h, but without citing any authority. Piazzi sets down 96 and 97 Virginis and 38 Herculis as variable stars. [The blood-red star, 4b 51m 50.9', 1020 2' 4" (1850), discovered by Mr. Hind, is stated by Schmidt (Ast. Nachr. 760.) to have been seen by him 6m. in Jan. 1850, and to have totally disappeared in Dec 1850 and Jan. 1851.] '
(826.) Irregularities similar to those which have been noticed in the case of o Ceti, in respect of the maxima and minima of brightness attained in successive periods, have been also observed in several others of the stars in the foregoing list. x Cygni, for example, is stated by Cassini to have been scarcely visible throughout the years 1699, 1700, 1701, at those times when it was expected to be most conspicuous. No. 59 Scuti is sometimes visible to the naked eye at its minimum, and sometimes not so, and its maximum is also very
irregular. Pigott's variable star in Corona is stated by M. Argelander to vary for the most part so little that the unaided eye can hardly decide on its maxima and minima, while yet after the lapse of whole years of these slight fluctuations, they suddenly become so great that the star completely vanishes. The variations of a Orionis, which were most striking and unequivocal in the years 1836—1840, within the years since elapsed became much less conspicuous. They seem now (Jan. 1849) to have recommenced.
(827.) These irregularities prepare us for other phænomena of stellar variation, which have hitherto been reduced to no law of periodicity, and must be looked upon, in relation to our ignorance and inexperience, as altogether casual; or, if periodic, of periods too long to have occurred more than once within the limits of recorded observation. The phænomena we allude to are those of Temporary Stars, which have appeared, from time to time, in different parts of the heavens, blazing forth with extraordinary lustre; and after remaining awhile apparently immovable, have died away, and left no trace. Such is the star which, suddenly appearing some time about the year 125 B.C., and which was visible in the day time, is said to have attracted the attention of Hipparchus, and led him to draw up a catalogue of stars, the earliest on record. Such, too, was the star which appeared, A. D. 389, near a Aquilæ, remaining for three weeks as bright as Venus, and disappearing entirely. In the years 945, 1264, and 1572, brilliant stars appeared in the region of the heavens between Cepheus and Cassiopeia; and, from the imperfect account we have of the places of the two earlier, as compared with that of the last, which was well determined, as well as from the tolerably near coincidence of the intervals of their appearance, we may suspect them, with Goodricke, to be one and the same star, with a period of 312 or perhaps of 156 years. The appearance of the star of 1572 was so sudden, that Tycho Brahe, a celebrated Danish astronomer, returning one evening (the 11th of November) from his laboratory to his dwelling-house, was surprised to find a group of country people gazing at a star, which he was sure did not exist half an hour before. This was the star in question. It was then as bright as Sirius, and continued to increase till it surpassed Jupiter when brightest, and was visible at midday. It began to diminish in December of the same year, and in March, 1574, had entirely disappeared. So, also, on the 10th of October, 1604, a star of this kind, and not less brilliant, burst forth in the constellation of Serpentarius, which continued visible till October, 1605.
(828.) Similar phænomena, though of a less splendid character, have taken place more recently, as in the case of the star of the third magnitude discovered in 1670, by Anthelm, in the head of the Swan ; which, after becoming completely invisible, re-appeared, and, after undergoing one or two singular fluctuations of light, during two years, at last died away entirely, and has not since been seen.
(829.) On the night of the 28th of April, 1848, Mr. Hind observed a star of the fifth magnitude or 5.4 (very conspicuous to the naked eye) in a part of the constellation Ophiuchus (R.A. 16h 51m 18.5. N.P.D. 102° 39' 14"), where, from perfect familiarity with that region, he was certain that up to the 5th of that month no star so bright as 9.10 m. previously existed. Neither has any record been discovered of a star being there observed at any previous time. From the time of its discovery it continued to diminish, without any alteration of place, and before the advance of the season rendered further observation impracticable, was nearly extinct. Its colour was ruddy, and was thought by many observers to undergo remarkable changes, an effect probably of its low situation.
(830.) The alterations of brightness in the southern star n Argûs, which have been recorded, are very singular and surprising. In the time of Halley (1677) it appeared as a star of the fourth magnitude. Lacaille, in 1751, observed it of the second. In the interval from 1811 to 1815, it was again of the fourth; and again from 1822 to 1826 of the second. On the 1st of February, 1827, it was noticed by Mr. Burchell to have increased to the first magnitude, and to equal a Crucis. Thence again it receded to the second; and so continued until the end of 1837. All at once in the be