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The young astronomer will avail himself of the useful hints suggested by this communication in the management of his instruments in viewing the present transit.
A very pleasing method of observing the phenomenon, will be by transmitting the sun's image through a telescope into a darkened room; the image of the sun can be received on paper, and the whole transit observed without distressing the sight.
The transits of Mercury, for many centuries to come, can take place only in the months of May and November. The first observation of this kind was made by Gassendi, in November, 1631, since which period they have been frequent. The following is a list of those that will happen till the end of the present century; those marked with an asterisk will be visible in this country.
1835, November 7th.
1881, November 7th:
1894, November 10th. A transit of Venus is a phenomenon of very rare occurrence, as will appear by the following list, which contains all those transits which have occurred since that which took place in December, 1639, inclusive, (the first that was ever known to have been seen by human being,) to the end of the 21st century. :
1639, December 4th.
1769, June 3rd.
1874, December 8th. * 1882, December 6th. * 2004, June 7th.
2012, June 5th. The transits of Mercury and Venus can happen only when they are in their nodes, and when the earth is in the same longitude ; for many centuries to come the transits of Venus can take place only in the months of June and December.
No such useful results can be expected from the transits of Mercury as from those of Venus, namely, the ascertaining or confirming of the distance of the earth from the sun : owing to the greater distance of Mercury from the earth than Venus, the difference of their parallaxes is so little, as always to be less than the solar parallax that is sought, and therefore Mercury is considered ineligible for solving that interesting problem which, in 1769, was so satisfactorily derived from the transit of Venus.
Mercury in aphelion on the 16th of this month. Stationary near 38 in Aries on the 17th. In conjunction with Venus on the 20th.
Venus at her greatest south latitude on the 1st. In conjunction with o in Pisces on the 7th, difference of latitude 4'; with o in Aries on the 21st, difference of latitude 1'.
Phases of Venus. The following are the proportions of the light and dark phases of Venus :May 1st.--Illuminated disc = 11.0224
Dark part = 0.9776
Mars in conjunction with Jupiter at 10 in the morning of the 26th, difference in declination 51'.
Hrs. Min. Vesta, 4th day. Right Ascension 8 44. N. Declin. 23° 56' 12th
.... 8 54. ..... 23 13 20th
22 24 28th
21 31 Juno, 4th
11 39 12th
11 38 20th
11 29 28th
11 12 Pallas 4th
4 57 12th
5 27 20th ...
5 54 28th
........ 6 17 Ceres, 4th
1 2. S. Declin. 2 9 12th
1 5 20th
1 24. .........
0 4 28th ........ .... 1 34. N. Declin. O 53
Eclipses of the Satellites of Jupiter. None of these will be visible this month.
Saturn stationary near 1 in Leo on the 10th. In quadrature at 30 min. after 2 of the morning of the 30th.
FORM OF SATURN'S RING.
Semi-conjugate axis - 4.25 Uranus in quadrature at 30 min. after 2 of the morning of the 9th. Stationary on the 22nd.
In ardent contemplation's rapid car,
Pierce heaven's blue curtain ; strike into remote ;
What behold I now!
Sphere of the Fixed Stars. Positions of the principal stars on the 1st of the month, at 10 in the evening.
Castor and Pollux near the western horizon. Ursa Major in the zenith. A line drawn from the polar star by 1 and u, in Ursa Major, points out Regulus, or the Lion's heart; another line, from the same point, through y in Ursa Major, passes through Denebola, or the tail of the Lion. Another imaginary line, through 8 and y in the Great Bear, passes through Leo Minor, Regulus, and Cor Hydræ. West of Cor Hydræ is Procyon, east is Crater and Corvus,—the latter formed of an imperfect square of four stars. Spica Virginis, Arcturus in Boötes, and Denebola, form an equilateral triangle, Arcturus the most elevated, and Denebola to the west. A line through ε and n, in Ursa Major, passes through Gemma in Corona Borealis; another line from Arcturus, through Corona Borealis, passes through Hercules to the bright star Vega in Lyra. Vega, Althair in Aquila, and Delphinus, form an isosceles triangle, of which Vega is the summit.
TELESCOPIC OBJECTS. Leo. Variable stars, &, 4, 25, and i. Double stars, w, both of which are red. 54, the largest white, the smallest greyish white. T, the large star red, the small star bluish. O, the large white, the small a pale red. i is a beautiful double star. 7, 83, and 88, are also double stars. 90 is a triple star. Regulus is a double star.
y, in Leo, is a binary system, the large star wbite, the small reddish white From the interval between the two stars, the ratio of their diameters, and the variation in the angle of position, it has been found that the apparent orbit of the small star is elliptical, and that it performs a whole revolution in about 1200 years in a retrograde direction. Between 9 and i are two faint nebulæ; two other nebulæ, of the same description, between p and I, - these nebulæ, though faint, are, in general, resolvable into stars.
Virgo. In this zodiacal constellation 20 and 91 are variable stars. Ę, J, T, are double stars. 7, in Virgo, is a binary system, both the stars of which it is composed are white, and nearly equal in magnitude; a revolution is performed about their common centre of gravity in 708 years. In and near the bosom and right wing of Virgo are no fewer than eighteen nebulæ, some of which are bright in the centre, but, in general, they are of a faint description.