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The Heavens in January

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The Heavens in January SCIENTIFIC AMERICAN January 2, 1915 The Heavens In January Weighing and Measuring a Star 200 Light Years Distant from the Earth By Henry Norris Russell, Ph.D. HE distances of many of the stars are now fairly tion. The larger star, 1,300,000 miles in diameter, does north one may, on the brilliant nights of winter, see T well known; their real brightness compared with not shine quite so brightly per square mile as the at their best the nebula of Andromeda and the great that of the Sun may frequently be calculated; we know smaller, so that the latter, though but 1,170,000 miles star cluster in Perseus (between this constellation and the densities of about ninety stars and the masses of in diameter, gives out eleven twelfths as much light as Cassiopeia) and then facing about, compare these with a rather smaller number. But there are very few the other. When the smaller star goes beh�d the Praesepe in Cancer-a cluster which, unlike that in ca>:es in which the actual size of a star-its diameter larger only a thin crescent of about one seventh the Perseus, is resolvable into its component stars in a in miles-can be determined, and, therefore, a new width of the whole disk remains in sight. This gives field-glass. instance of the sort well deserve>: discussion here. the principal (deeper) eclipse. When the small star From the very appearance of this cluster cme would 'l'he star in question, known as RX Herculis, is of comes in front of the larger, we get the secondary and judge that it was nearer than the other, and this is the seventh magnitude and quite invisible to the un­ shallower eclipse. probably true--though if Schwarzschild's estimate of aided eye. As its designation indicates to the initiated, The mass of each star is 89 per cent of that of the 500 light years for its distance be correct, as seems it i>: variable in brightness, and the fact that we can Sun (unusually small for a white star like this), and very likely, it is hardly what even an astronomer would determine its actual size adds to the discerning mind the density of the larger one is one quarter, and that ordinarily call a neighboring object. Kapteyn, in the the information that the variability must be due to of the smaller one third of the Sun's density. case of the Perseus cluster, ,eoncludes that it is prob­ eclip>:e and that it must have been observed with the If the stars give off as much light per square mile ably 1,600 light years off at the least, and perhaps very >:pectroscope. as does the Sun their distance from us must be such much farther. Attention was first called to this star when it was that light would take 200 years to travel it. But the As for the Andromeda nebula, hardly anyone would found that it lost about 40 per cent of its light at spectrum of the stars closely resembles that of Sirius dare even to guess at its distance, but as its spectrum intervals of 21 hours 20 minutes and 34 seconds, re­ or Vega, and it is very probable that stars of this sort resembles that of a star cluster, and no separate stars maining constant in brightness for all but about 5 are much hotter (at least on the surface) than the can be seen, even with the greatest telescopes, it may hour:,; of this interval. This behavior showed at once Sun, and shine far more brightly-giving out from- be vastly more distant still. Turning back to the east, that the loss of light must be due to an we find Leo well above the horizon, and eclipse by some attendant body, as in so Ursa Major coming up on the northeast; many other cases. and the familiar constellations about the �j)ectroscopic observations by Prof. pole complete our survey. J<'rost at the Yerkes observatory showed The Planets. that the Hnes in the spectrum became Mercury is practically invisible at the double in the interval between eclipses, beginning of the year, but comes out into and thu>: proved that the companion as the evening sky, and by the end of Janu­ well as the principal star was bright, so ary is well visible, setting at 6 :30 P. M. that their >:pectra appeared simultaneous­ By the end of the month he is close to ly when one was rushing toward us after Jupiter, and the two form a pretty pair, it had been eclipsed, and the other reced­ Jupiter appearing about twice as bright ing. Long series of accurate measures of as Mercury. the brightness of this star have been made Venus is morning star, and at her great­ ht Harvard by the late Prof. Wendell, and est brilliancy as the year opens-twelve at Princeton by Dr. Shapley (now of the times brighter than Jupiter. She ri>:es at Mount Wilson staff), by whom the calcu­ 4 A. M. or a little after all through the lations here described have been carried month, and is the glory of the morning out. sky. These two sets of measures agree per­ Mars, having just passed conjunction fectly, and show that, outside the eclipses, with the Sun, is theoretically a morning there is not the least variation in light. star and practically invisible. Successive eclipses, however, are slightly Jupiter is evening star in Capricornus unequal in magnitude, the maximum ob­ ano visible now only in the early evening. servation being alternately 40.8 and 35.7 Saturn is in Gemini, just past opposition per cent of the light at maximum. This and a splendid object both to the 'eye and >:mall difference is demonstrated beyond telescope. He i>: so bright that he quite question by the observations. Its explana­ ; changes the appearance of even the bril- tion is fairly obvious. The two stars, liant region of the heavens through which which revolve around one another, are he,fs passing. slightly unequal in brightness. One gives ti;anus is so low in the west at sun­ off a little more light per square inch down as to J:je unobservable. Neptune, on Feb. 6. At 11 o'clock: Jan. 7. At 9 o'clock: the other hand" is in oppo>:ition on the than the other, and so when the former At 10'h o'clock: Jan. 14. At 8'h o'clock: Feb. 14. i>: eclipsed a little more light is lost than At 10 o'clock: Jan. 22. At 8 o'clock: Feb. 21. 19th, and favorabiy placed. On December At 9'h o'clock: January 29. in the opposite case. As the stars circle 31st his right ascension is 8 hours 6 min­ about their common center of gravity, utes 46 seconds and his declination 19 each in turn partially eclipses the other, NIGHT SKY: JANUARY AND FEBRUARY degrees 52 minutes north. On February and the observed situation follows. The 1st these co-ordinates have become 8 hours aetual period of revolution must then be double that six to ten times as much light per square mile. On this 3 minutes 5 seconds, 20 degrees 4 minutes north. This between eclipses, or 1 day 18 hours 41 minutes 8.79 basis, therefore, the distance of the system may be puts him about 8 degrees west of Praesepe and 2 de­ >:econds, according to Dr. Shapley. As the time of the estimated as 500' light years (or thirty million times grees north of the fine triple star � Cancri-where the middle of eclipse can be determined within a very few the distance of the Sun), and the light emission of the observer who has a three-inch telescope and a star­ minutes, and it has been under observation for four­ pair as fuUy thirty times that of the center of our chart, or the patience to make one for himself, may teen years, or nearly 3,000 revolutions of the system, it system. If this be true the eclipses recently observed find him. is clear that this value can be at most a couple of actually took place long before Columbus discovered The Moon i>: full at 7 A. M. on the 1st, in her last hundredths of a second out of the way. the New World, and more than ten thousand other quarter at 4 P. M. on the 8th, new at 10 A. M. on the The orbits in which these two stars move about their eclipses of each star by the other have happened since, 15th, in her first quarter at 1 A. M. on the 23rd, and center of gravity must be practically circular; for the and a're, so to speak, on their way to us-the light full again at 11 P. M. on the 30th. She is nearest the shallower eclipses come just half way between the which will announce them being still far in the depths Earth on the 12th, and farthest away on the 24th. She deeper ones and last equally long, and if the orbit was of interstellar space. passes near Venus on the 12th, Mars on the 14th, eccentric this could not be the case. It is really amazing that, by means of observations Mercury on the 15th, Uranus on the 16th, Jupiter on So much has now been found out about this system which, if a full account was kept of the time taken, the 17th, Saturn on the 27th, and Neptune on the 30th.
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