ROUGH ASTRONOMICAL NOTES

Evening Star, Issue 3673, 30 November 1874, Page 2

ROUGH ASTRONOMICAL NOTES

DECEMBER, 1874. 1. The Sun.—lf there is truth in the theory that the solar spots are to a large extent caused by the attraction that the planets exert on its cloud envelope or photosphere, then there ought to be, on or about the 9fch of December, a very good display of spots. At that time the Earth will he fast approaching its perihelion or smallest distance from the Sun, where of course its attraction would be greatest; and the Earth and Venus will at that time, being in the same straight line with the San, be acting upon it with the greatest effect possible. On Saturday last there was a good-sized spot nearly on the centre of the Sun’s disc ; it was made double by one of the ordinary “ bridges,” and was surrounded by a well defined penumbra. The Sun attains'i is greatest southern decl nation on the 22nd nst., at about half-past ten o’clock in the morning. At that time summer is technically supposed to commence. 2. The Moon will be at its greatest distance from the Earth just after noon on the sth, and at its least distance just before noon on the 20th. The phases of the Moon will take place as follows : Last Quarter ... Dec, 1 ... 5.50 a.m. New Moon ... ~ 9 ... 11.28 a.m. Eirst Quarter ... „ 16 ...11.46 p.m. Full Moon ... „23 ... 4.18 p.m. Last Quarter ... ~ 31 ... 1.57 a.m. An occultation of Jupiter by the Moon will take place on the morning of the ath. The time of conjunction of the centres of the Moon and of the planet Jupiter is 3 a.m. The Moon’s passage over the planet will of course commence some time before this. We have sent Homo for the “ Tables ” that are necessary for calculating the exact circumstances of an occultation for any given place, unless these calculations are to be made by a person who has an unlimited amount of time at his dia posal. We hope to be able in future to foretell occultations with due accuracy. At present we can offer only the somewhat vague prediction given above.

3. Mercury will be visible in the mornings at the beginning of the month. It will be at its greatest elongation W. (20deg. 21min.) on the 2nd of the month. At that time it will be in the constellation Libra, and will form nearly an equilateral triangle with the stars Alpha and lieta of that constellation, and rising just after them. It will rise nearly an hour and a-half before the Sun, about seven degrees to the north of his track. 4. Venus,—This planet may probably be caught sight of at the very beginning of the month, just after sunset. It will then cease to be an evening star for nearly a year. In the telescope it now presents the appearance of a very young moon. Soon after the middle of the mouth Venus will be visible in the mornings, and at the end of December it will be fast approaching its period of greatest brilliancy. Venus has, during the last few months, • received a very large share of attention. This has been owing partly to her great brilliancy, and to her being extremely favorably situated for observation ; but still more to the curiosity which has been excited with regard to the coming transit. Venus will pass over the Sun’s disc on the 9fch of December. Shortly after one o’clock in the day telescopic observers will see a slight indentaDion ou the Sun's disc at a point just below that part of the Sun which will then be furthest to the right. About half an hour afterwards the whole of the planet will be seen fairly on the disc, but clinging, so to speak, to its edge. It will then gradually pass over the disc in a slanting direction till the time of egress, when it will leave the Sun nearly at that point which is nearest the horizon— i.e., at the bottom of the Sun. At about a quarter to six the whole thing will be over. Those who have _ astronomical telescopes will hardly require to be reminded that the first external contact will take place on the left side of the Sun’s reversed image. A good binocular, armed with a proper.shade of colored glass, mil give a very fair view of the greater part of the transit. It should be remembered that it is extremely dangerous to look at the Sun with any kind of telescope unless it is properly protected. As a pis alter a piece of smoked glass may be used by those who have no other means of viewing the transit. The planet will oe quite visible on the Sun’s face as a black dot, even with this simple appliance, when once it is fairly on the disc, the apparent diameter of the planet at the time being about one-thirtieth part of that of the Sun. The diagram in the Athenaeum, drawn, we believe, by Mr A. H. Ross, shows the real path of the planet across the Sun’s disc, as referred to the north point of the Sun. As the transit advances, however, the Sun, so to speak, gets canted over, and thus the appearances described above are produced. The following are the approximate times of the phenomena of the transit First external contact ... Ihr. 12min. p.m. First internal contact ... Ihr. 41min. p.m. Last internal contact ... shrs. 15min. p.m. Last external contact ... shrs, 45min. p.m. . The times here given are local meantime. It is to be hoped that all those who have telescopes will "use them on this occasion, and that they will carefully record, at the lime, everything that strikes them as being worthy of notice. There is no saying when or how some fact worthy of attention may be brought to light. It is not mifrequently the case that a phenomenon escapes the notice of hundreds of observers, and yet is seen by one or two. At all events, no possible harm can result from keeping a record of facts observed, even should these turn out to be unimportant, 5. Mars is visible in the morning. It is, however, too far from the Earth to be very well seen. It is now, at the beginning of the months, in the constellation Virgo, about Odog. from the bright star Spica. The ruddy color of the planet presents a pleasing contrast with the brillant white of the star. Pj Vesta. This asteroid is now, November 29th, in opposition to the Sun. Owing to the unfavorable weather, we have not been able to see it, but it may be looked for at about midnight on December Ist, in the constellation Taurus, not far above the bright star Aldebaran, betweeuthe two fourth magnitude stars, Delta ! wid Ri, of that constellation, A good opera

glass would certainly show the asteroid. It may be distinguished from surrounding %(pnall stars by its motion from day to day. 7. Jupiter is now a morning star. Its brightness is increasing. On the first of the month it will lie in the constellation Virgo, forming a beautiful triangle with Mars and Spica. 8. Saturn. Those who wish to see this planet must make the best use of their time, as it will for some limo be practically invisible soon after the end of the present month. It is in the constellation Capricorn in a barren part of the sky. It will he pretty near the Moon on the 13th of the month. 9. Uranus and Neptune. The former planet will be in opposition next month, when wc sli dl givi; directions for “fishing it up ” Neptune is sfil an evening star, and still very ne i r its old place. The asteroids Ceres and Astrnea will be in opposition during the present month, but the foimor is too far north to be at all well seen, while the latter is too small an object to be interesting to ns who are merely star-gazers.