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On the Observation of North Polar Stars in the Vertical of Polaris

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On the Observation of North Polar Stars in the Vertical of Polaris 379 3069 380 R log E n Virg. y Cass. a Can. Maj. a Can. Min. a Aur. Saturn a Tauri a Orion. E -0.26 +0.32 +0.25 4-0.3 7 +0.07 +a32 -0. j6 -0.35 -0.57 0.55 -0.19 +0.14 +O.IO +O.IO -0.04 +0.08 -0.20 -0.14 -0.38 0.65 -0.12 i-o.04 to.03 +O.OI -0.03 +0.03 -0.11 -0.04 -0.23 ' 0.76 -0.07 0.00 +o.or 0.00 - 0.0 I +o.o I - 0.06 -0.02 -0.11 0.85 -0.02 0.00 0.00 0.00 0.00 0.00 -0.02 0.00 -0.02 0.95 +0.02 +o.or 0.00 -0.01 +o.o I 0.00 0.00 +O.OI +0.05 1.05 +0.06 +0.0 I 0.00 -0.02 +o.or -0.01 +o.or +0.02 to.10 1.15 +0.09 -0.04 0.00 - 0.03 - 0.03 -0.0.3 fo.03 +0.02 +o.ro 1.23 +O.I2 -0.17 -0.04 -0.10 -0.10 -0 09 +0.04 -0.01 to.08 1.32 +0.14 -0.37 -0.14 -0.2 I - 0.2 3 -0.22 +a03 -0.12 +0.03 1.38 +0.16 -0.59 -0.26 -0.35 - 0.40 -0.36 +0.02 -0.26 -0.04 1.45 +0.18 -0.83 -0.39 --0.51 - 0.6 I -0.5 I +o.o I -0.43 -0.12 1.51 +0.20 - 1.10 -0.54 -0.7 I -0.84 -0.67 0.00 -0.63 -0.21 1.58 In the case of sunlight, a small correction should be I cated. Perhaps, however, Saturn is really bluer than the applied for the selective reflection of the silvered glass Sun in which case the values already given are correct. mirror. This effect does not appear to be large, since the The curve for a Aurigae is nearly the same as that of spectrum of Saturn gives nearly the same results as that a Canis Majoris which shows that although its lines are derived from direct sunlight, except for rays of short the same as those of the Sun, the distribution of its light wave-lengths. The negative values derived from these rays resembles that of a first type star. The red color of in the case of Saturn may be due to the selective reflec- a Tauri and a Orionis as compared with a Virginis and tion above mentioned. The corresponding residuals of the a Canis Majoris is clearly shown by the change in sign of other spectra might be corrected by the amount thus indi- the residuals. Observatory of Harvard College, Cambridge Mass. U. S. A., 1891 Oct. 31. Edward C Pickering. On the Observation of North Polar Stars in the Vertical of Polaris. By Trttrnnn Henry Saford. It is comparatively quite easy to determine the right ioubtful how far I can carry this independence in the ascension of a Ursae minoris by double culminations. imited time allowed by other occupations. It is quite easy Other standard polars as 6 Ursae minoris or 51 H. Cephei o me, as for many others, to spend a good many evenings are not so easily observed in the daytime, and therefore n observing; but not so easy (without neglecting other require a better organized service of observers than is found luties) so to employ other parts of the day. in many places. In studying over these matters I have fallen upon a It is not very easy, again, to connect other polnrs nethod Rhich seems to me promising to be available some with double transits of Polaris. This is especially true in .ime in the future. the region about 6h and 18~,but is quite sensibly felt on It is to observe a number of (not too close) polars both sides of these right ascensions. n the Vertical of Polaris. The simplest case is that in These difficulties would be of far less consequence which the greatest difficulties are felt in using the ordinary if it were not quite important that there should be more method. Let us suppose a portable transit with adjustable independence in the various polar catalogues than now seems 3ase to be fixed in such a position that Polaris shall be to exist. The form of the personal equation between slow- 3ear its mid wire at the eastern elongation. This will occur and quick-moving stars depends - whatever method %bout 19~23~of sidereal time. is employed in their observation - on so many compli- 'The two stars cated and little-studied psychophysical processes, that astro- Position 1891.0 nomers cannot be quite sure of the application of the for- Camelopardalis 2 5 H. 7h %"+82O37' mulae. I allude to this here only to emphasize the Schwerd I 172 = Carrington 2965 19 29 + 83 15 necessity which I myself feel of attempting to make more will pass the same vertical within about half an hour of independent determinations of standard polar right ascen- this time; the latter, above pole, earlier than the pole star sions. reaches its elongation; the former, below pole, later. Ex- As I have at my disposal only an unsymmetrical pair perience shows that a well made instrument will change its of collimators, the one an ordinary telescope with micro- azimuth and polar deviation very little indeed during this, meter and fixed wires, and for declination pivots and a level, period; so that, with or without level readings, the right the other a lens of IOO feet focal length, with a mark ascension of the two smaller stars will be accurately obtained. mounted on a brick pier at that distance, I am somewhat The right ascension of Polaris does not enter into its azi- 3069 382 muth at elongation; which is dependent solely upon its >as an aperture of z inches French; carrying a power of 72. declination and the latitude of the place; while the polar [t is rather too small for results comparable in accuracy deviation (Bessel’s n) is substantially equal to the star’s with those of the Repsold meridian circle, but I intend to polar distance. try the experiment with it in order to settle details of Prof. Boss’s researches give the probable error of this methods, both in observing and reducing. polar distance as & 01‘03 for 1875, by observations no later Other stars, of different right ascensions, and gra- than 1876. We may safely assume that a new calculation dually increasing declinations as we approach the right would give no greater value for the present day. This ascension of Polaris or its opposite, can also be readily oh- value has nothing to do with the observer’s personal equa- served. In’their reduction, howewer, each astronomer must tion ; and is considerably less than the probable error which employ his own independent determination, by double would arise from employing a standard right ascension of transits, of Polaris. Under that condition there will be no Polaris in the meridian. The probable difference of an great difficulty in preparing a catalogue of standard polars observer’s individual right ascension of Polaris from a general in the declinations + 8z0 to + 84O and in all right ascen- mean cannot be less than & OSOI z sec 6, or f 0!’18 in arc sions. These will be, however, not quite homogeneous, of a great circle; see the paper which I published in 1864 unless the astronomer observes transits uniformly with his in the 6thvolume of the Proceedings of the American Aca- two different instruments. The easiest way to secure this demy of Arts and Sciences. uniformity (in my case) is to modify the meridian circle On the other hand, I find that with our present work by the use of a low power and a reversing prism, knowledge of the declinations of the two stars mentioned, and if needful a wire screen, so that it shall show the star with probable errors of < & 01‘2 and 0:‘3 respectively, as to magnitude, velocity, and direction of motion, like the their right ascensions would be rendered uncertain by smaller >broken< transit. This will give results whose diffe- -+ o?ooz sec d and & 0!004 sec d respectively. rences from the ordinary ones can be directly applied. In the formula After such a catalogue of the more distant polars has been made it is quite easy to interpolate among them 7 + dt + m + n tg d (using nearly simultaneous upper and lower culminations of an error in 6 will produce one in n tg d of the amount the various stars) observations of those nearer the pole: n sec2d Ad sinI” At present the chief object to be aimed at is to furnish or for n = ro17’, 1.36 d6 for 25 H. Camelopardalis, and accurate and thoroughly independent values of both coor- 1.62 Ad for Schwerd I 172. It is easy enough however to dinates of about zoo stars within 6’ of the north pole; determine these stars’ declinations with enough greater accu- these will provide zero points for the proposed number of racy to diniinish these resulting errors; of course they are photographic plates zo square, and consequently help settle much less sensible at the parallels of declination on which the places of all stars in that region. the stars are, But, all told, the probable errors dependent In concluding let me suggest that the process is, within upon anything but the transit of the star to be determined rather narrow limits, susceptible of reversal.
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