ROUGH ASTRONOMICAL NOTES

Evening Star, Issue 3881, 2 August 1875, Page 3

ROUGH ASTRONOMICAL NOTES

August, 1875. Sun.—The northern declination of the bun is now rapidly decreasing ; in three days he moves almost a degree nearer to the Equator ; consequently the length of the days is now fast increasing. Very few solar spots have been visibie during tho past month, and those that have been scon have been very minute; but the epech of minimum frequency of spots is now probably past, and we may expect the Sun to gradually become a more interesting object than he has been for some time past. 2. The Moon will bs in apogee at about halfpast six on the evening of the 10th, and will bo at her least djstance from the Earth on the night of the 25th, at about ha'f-an-hour before midnight. The phases will take place as fob lows * New Moon, on the 2nd, at Olir 57min a.m. First Quarter on the 9th, at 3hrs Omin p.m. Fnll Moon on tho 17th, at Ihr 4zniu p.m. Last Quarter on the 24th, at Ihr Bmin p.m. New Moon on the 31st, at llhrs Ilium a.m. The Moon will occult the planet Mars on the afternoon of the 12th. The immersion will take place shortly after sunset, and before the twilight is very far advanced ; but it will be quite easy to see the phenomenon with anything deserving the name of a telescope; a good opera-glass will show it, and, if tho weather should be fine, it ought to be visible to tho naked eye. The emersion will take place under very favorable circumstances. Occultations of Mars are not very rare occurrences ; but ir, is seldom, indeed, that such a one happens as that which wiU take place next Thursday week. We were fortunate enough to get a momentary glimpse, through a large telescope, of Venus when she was crossing the Sun’s disc last December. That was a sight well worth s.-eina • but we believe that Mars passing behind the Moon s disc, and coming into view on the other eide, will afford a far finer spectacle, As some

of our readers would probably like to be told what to look for, we shall state briefly what they ought to do, and what they may expect to «ee, always supposing that our calculations prove to be tolerably correct. It is supposed that an ordinary “spy-glass” is to be used; those who have astronomical telescopes will find all the particulars they require in an appended note. If an observer look at the Moen at five o’clock on the afternoon of the 12th, he will see, when the glass is exactly “ in focus,” near the lower part of the Moon but a little to the right, a nearly round, reddish looking disc ; this is, of course, Mars, At thirteen minutes past five he will see a slight indentation on that side of the disc which is turned towards the Moon. Mars then will have begun to pass behind the dark limb of the Moon. This indentation-will gradually increase, or, in other words, the planet will slowly pass out of sight behind the Moon. This phenomenon is cal’ed the immersion of the planet. At about a quarter past six the observer should direct his glass to the bright left side of the Moon ; in a short time (two or three minutes) he will see a minute red dot or •■-peck make its appearance. Gradually the Moon’s apparent motion will expose more and more of the surface of Mars, and at last the planet will have completely emerged from behind the disc, and the occupation will be over. Words can give no adequate conception of the impression which is made on the imagination by such a spectacle. We know of nothing that is more calculated to give one an idea of the grandeur and majesty of the motions of the heavenly bodies than a sight of this kind. A person who beholds it for the first time is made to feel the reality of the sublime truths of astronomy with a certainty of conviction that no amount of mere reading can possibly produce. We would stronglv advise those of our readers who can beg or borrow a decent telescope not to lose an opportunity that may never again come in their way. •Ve should be glad if anvone who may happen to notice anything peculiar with regard to the occultatiou would make the fact public through our columns. It not unfrequently happens that while hundreds of observers are engaged about the same phenomenon, one notices something that entirely escapes all the rest. If the weather should prove unfavorable, it may happen that only one or two observers may catch a glimpse of the occultation. Under these circumstances it would bo well if the exact time at which the phenomena take place could be noted by them.f 3. Mercury will be unfavorably situated for observation during the whole of the month. He will he in superior conjunction with the Sun on the 22nd.

4. Venus. —Nearly the same remarks may be made with regard to this planet. She is very far north, and passes the meridian about fifty-two minutes before the Sun. She may be caught sight of a short time before sunrise, but she will be quite close to the horizon. She may, however, be very fairly seen at about eleven o’clock in the day by those who have access to an equatorially mounted telescope. 5. Mars is still a magnificent object. In the telescope he is becoming markedly gibbous, like the Moon a day or two after the full. His light is now somewhat less than that of Jupiter, and it will soon begin to wane very rapidly. He passes the meridian at about five minutes to nine in the evening. G. Jupiter, too, is still a fine object. He is not yet very far from Spica Virginia, but he is beginning to move more rapidly towards the cast among .the. stars. He sets at about 11.34 p.m. 7. Saturn will be in opposition to the Sun on the 16 th, when, of course, he will pass the meridian ;it midnight. He is slowly moving west towards the star Delta Capricomi. He rises now at about fifteen minutes past six in the evening, somewhat to the S. of E,, and is visible all night long. Our account of the present appearance of this planet must he deferred till next month.

8. Uranus is at present lost in the Sun’s rays.

9. Neptune is still a morning star, and not far from his old place. He never is.

•Unless the contrary is stated, mean New Zealand mean time is used in these notes—that is to say, the time shown by the post office or the University clock. Time is generally given to the nearest minute, but in notes intended for the use of stargazers it is not thought necessary to aim at very great accuracy unless in special cases. fThe immersion will take place at shrs. smin. p.m., at an angle of 93deg. E. from N. point; the emersion at filirs, 9smin. p.m., at an angle of fildeg. W. from N. point. The nearest approach of centres of Moon aud Mars 6min. 44secs. of ate, will j occur at shrs. 37min., Local mean time being used. The occultatiou has been calculated for lat. 45deg. 55min. S., and for long, llhrs. 22min. E. Those who have calculated occupations, or eclipses of the Sun know that the work is not easy, and that it is necessary to wade through a perfect sea of figures in order to obtain even a moderately accurate result, while a single incorrect figure may easily cause an error of several minutes. It is believed, however, that the times and angles given above will be not very far wrong. In the computation certain minute quantities were neglected, e.g., the motion of Mars in his orbit during the progress of tho occultation; but this should not affect the accuracy of the results to any great extent. At all events, those arrived at by a method of projection recommended by Loomis, in which the effect of such omissions would he almost nil, and those obtained by computation show a satisfactory amount of agreement.