Brooks's Comet How to Find It Without the Aid of a Telescope By S. A. Mitchell, Professor of Astronomy at Columbia University THERE is hardly a person anywhere who is not A interested in a comet, and at the present time one is visible each night without the aid of a telescope. Moreover, it is not at the limit of visibility to the naked eye, but one which, Can be readily seen by anyone who cares to spare a few minutes watching for .. The comet known to astronomers as Brooks's, or Comet 1911c, was discovered on the night of July 20th by the famous comet·seeker at Geneva, N. Y. When discovered, it appeared as a faint hairy star, without' a tail, entirely unlike the popular idea of a comet. Observations on this and the following few nights gave astronomers the opportunity of calculating its path with respect to the sun, and in relation to the earth. These calculations furnish an ephemeris which gives the position in the sky where the comet may be found. Such a calculation is a laborious piece of work, which must be done with great precision, and with care that no mistakes are made in tlle additions and subtractions. Ordinarily when a comet is discovered a parabolic orbit is first computed, for this calculation is the easiest and presents the fewest difficulties. Such an orbit is quite an impossible thing in astronomy, but on account of the simplicity, it is adopted because it give\ the position of the comet near enough for all practical purposes. If the comet is an Interesting one, or if it is the return of one formerly discovered, then the more difficult elliptical elements are calculated. In the case of Halley's comet, this was an exception any difficult undertaking, for the “perturbations” or attraction of the various planets led to serious complications. Several sets of calculations have been made for Brooks's comet, one of the most reliable being that of F. E. Seagrave of Providence, R. I. The ephemeris for the end of September and beginning of October follows: Date. Right Ascension. Declination. h. m. 8. deg. m. 8. September 21st .......... 15 31 15 + 53 0 39 September 25th .......... 14 51 17 49 21 7 September 29th..........1 17 44 44 58 56 October 3rd ........... 13 49 52 40 6 42 October 7th ........... 13 26 46 34 51 0 The amateur with his small telescope and circles can readily find the comet from this table. Right ascension and declination in the sky correspond to longitude and latitude on the earth. A ship at sea is located 'byVknowing- its longitude and latitude, or New York city -is found by knowing that its longitude is 74 degrees west. and its latitude 40 degrees 48 minutes north. The stars are kept track of by means of their right ascensiors and declinations. As we can locate Philadelphia from the fact that it is ninety miles in a certain direction from New York, so we can locate the comet from its position with respect to the stars without paying attention at all to the figures which give the right ascensions and declinations. The path of the Brooks comet. On September 2nd a photograph by Prof. Barnard exhibited a tail eight degrees in length, which corresponded in extent to 10,000,000 ' miles. At the same time the head measured 500,000 miles across. The comet was closest to the earth on September 17th, when it was readily visible as a fourth magnitude star. It was then forty-eight million miles away from us. Steadily the comet is speeding toward the sun, the great central luminary which exerts its attractive influence on all bodies of the solar system. On October 27th, the comet will be at perihelion, when it will be 45,000,000 miles distant from the sun, which is as dose as it will approach that body; At the middle of September, the comet was a circumpolar object at 57 degrees north declination. Its motion has been southwest more than a degree each day. On September 30th, the comet will be as bright as the fifth magnitude and can be quite easily found near the end of the handle of the “Big Dipper.” The handle takes a crook in it at the well-known double star Mizar. Follow from Mizar to the end of the handle, and in a straight line five degrees farther on, the, comet may be seen; or in other words, the comet will be about half way between the end of the handle of the “Dipper” and the third magnitude star Gamma Bootis. The comet will set about 10 o'clock. One should look for it immediately after sunset (though the moon will interfere somewhat) before the comet gets too near, the horizon. The comet's rapid motion makes it set earlier each night, so that on Oetober 7th it sets at 9 P. M. It will soon set as early as the sun when it will become invisible-to be seen later in the month before sunrise. Though the head of the comet has been quite bright, its tail has been difficult to see in the telescope because it is so faint. It needed a long exposure to photograph the tail. The world is still waiting for a brilliant comet to appear, one which may be seen in the sky in spite of the electric lights of the city and without special diagrams, one which will rival the great comet of 1882.