CELESTIAL OBJECTS. THE singular circumstance that two comets, very similar in appearance, should be visible to the naked eye at about the same bearing and altitude, within six months of each other, has naturally attracted almost universal attention. The slightest acquaintance with the motions of the heavenly bodies sufficed to show at a glance that the two objects were not identical; and the investigation of the orbit of the latter has established that, unless it has undergone extraordinary changes from the attractions of the other bodies of our system, no former visit of this Comet has been recorded with suffi cient accuracy to enable us to identify it. When the Comet first appeared, toward the end of March last, it shone, as its predecessor, a little north of west, with the brilliancy of a star of the second magnitude; its tail, about four degrees in length, pointing upward from the stellar nucleus, and gently curved, with the concavity toward the northern azimuthal point. With the twenty-five feet refractor at Markree, the nucleus appeared as an undefined mass of light, increasing in brilliancy toward the centre, and having a distinct coma on the side opposite to the tail. A curious appearance, but one not unusual in such bodies, was a dark space behind the nucleus, as if the matter composing the tail were shot out from the nucleus, and did not become visible until it had reached a certain distance. From a first approximation to the elements of the orbit, founded on the Markree observations of March 30th, April 1st, and April 3d, it was expected that the Comet would have remained visible to the naked eye, and afterwards in the telescope, considerably longer than proved to be the case. This proceeded, not from any error in the observations or calculations,-the orbit thus found turned out to be unexpectedly near the truth,-but from a much more rapid diminution of light than theory would indicate. In fact, from the brightness of a star of the second magnitude on March 30th, it had dwindled to that of a ninth-magnitude star on April 15th. A comparison of the distances from the Earth and Sun led us to expect that the light on the latter occasion would be between six or seven times less than on the former, or about equal to that of a star of fifth or sixth magnitude. We here insert two sets of elements of the orbit: the first approximation, that which has been alluded to; the second, from the Markree observations of March 30th and April 15th, and an observation made at Paris on April 7th : The second approximation represents the observed places, selected with extreme accuracy; and, as it is founded on the hypothesis that the Comet moves in a parabola, there is not, therefore, the slightest probability of our being able to predict the return. Some of our readers are doubtless aware that the parabola is not a closed curve, like the circle or ellipse, and that, consequently, if the orbit were strictly parabolic, the Comet would never again visit us. To convey a popular idea of the position of the orbit, suppose it a visible material curved line. This line intersects the plane of the Earth's orbit in two points diametrically opposite, with regard to the Sun. One of these is in the line which would connect the Earth and Sun on the 8th of August next; that is to say, in a line directed from the Sun to the middle of Capricornus. The Comet was at this point on the 2d of March, at 10h. 13m. in the morning, in passing from the southern to the northern side of the plane of the Earth's orbit. Its distance from the Sun at this moment was 66 millions of miles; and from the nearest point of the Earth's orbit, 30 millions; from the nearest point of the orbit of Venus it was only 3 millions of miles distant. From us the distance was then 157 millions of miles, and the angular distance from the Sun 10° 42' westward. Let the reader fancy himself standing at this point of the orbit, on the northern side of the plane of the ecliptic, with his face toward the Sun: the orbit would appear to rise almost perpendicularly, inclining only seven and a half degrees from the vertical toward his left hand. The orbit becomes gradually more curved as it ascends, and approaches the Sun, until it reaches its nearest (perihelion) distance, 26,421,000 miles, at a point only 11° 38′ beyond the highest point of the orbit. The Comet was here at twenty minutes after noon on the 24th of March: thence, descending, it arrived at its least distance from the Earth, 80,600,000 miles, about eight o'clock in the afternoon of April 1st. It crossed the plane of the Earth's orbit a second time, on April 5th, at 10h. 46m. in the morning, when its respective distances from the Sun and Earth were 44 and 83 millions of miles: it was 12 millions of miles without the orbit of Mercury. The greatest distance, which, as has been remarked, is literally incalculable from the data furnished by the observations made during this apparition, is of course in a direction precisely opposite to the least, and therefore almost perpendicularly southward of the plane of the ecliptic. The distance of MERCURY from the Earth on June 1st is 125, and on July 1st 82, millions of miles. From a disc almost full at the beginning of the month, he will change to the appearance of the Moon at the end of her first quarter. The table shows that on the 21st he sets more than an hour and a half after the Sun. On the 9th he will have attained his greatest angular distance from the plane of the ecliptic, as seen from the Sun, 7° north. To an inhabitant of this planet, Venus will be in conjunction with the Sun on the 10th; Mars in opposition on the 28th; the Earth a conspicuous object in the morning sky; Jupiter near the Earth; Saturn approaching the Sun westward. VENUS recedes 22 millions of miles during the month. She will be at her greatest distance from the Sun, 69,450,000 miles, on the morning of the 2d, at 2h. Her form is, of course, gibbous, approaching full. The diameter at the end of the month is only one-third that of Jupiter, and the light considerably diminished: notwithstanding this, she maintains her distinction as morning star. She will be near Uranus on the morning of the 18th, and near the Moon on the afternoon of the 21st. Seen from this planet, Mercury will, after the 10th, be coming out from the Sun eastward, and approaching Mars. The Earth, still farther eastward, will be peerless in their evening sky: its angular distance from the Sun on the 16th will be about seventy degrees. Considerably farther to the east is Jupiter, which, as well as the Earth and Mars, is approaching the Sun. Saturn and Uranus are receding westward. MARS, as Venus, will be 22 millions of miles further from us at the end of the month than at the beginning. He is approaching the Sun, or rather the Sun appears to be gaining on him, both moving eastward. On the 2d he will be in quadrature, that is, ninety degrees distant from the Sun. On the 3d he will be near the Moon, somewhat southward. Viewed from this planet, Mercury would appear as a crescent, approaching the Sun on the eastern side, and would be in conjunction on the 28th; Saturn, somewhat further eastward, also approaching the Sun; Venus, gibbous, and nearing the Sun on the western side, her angular distance on the 16th about seventeen degrees. The Earth would be morning star; its elongation from the Sun forty degrees; form, that of the Moon, at the end of the third quarter. Jupiter would be still farther westward. JUPITER can now be seen at no very inconvenient hour; but so low, that the pleasure to be derived from the examination hardly compensates for even a slight inconvenience. His apparent magnitude is that of a ball one inch and a half in diameter, at a distance of two hundred yards. SATURN and URANUS are too near the Sun to attract attention. On the 21st, at 7h. in the evening, the Sun will have attained his greatest northern declination, 23° 27′ 34′′; and then commences "The summer! the summer! the exquisite time Of the red rose's blush and the nightingale's chime; The chant of the lark and the boom of the bee. I have scented the breath of the fresh-open'd flowers, I have pluck'd a rich garland from bright hawthorn bowers; My footsteps have been where the violet sleeps, And where arches of eglantine hang from the steeps; I have startled the linnet from thickets of shade, And roused the fleet stag, as he bask'd in the glade; For the summer, the golden-crown'd summer, is here!" RISING AND SETTING OF THE SUN, FOR THE PARALLELS OF THE MERCURY. VENUS. MARS. JUPITER. SATURN. URANUS. SUN. Rises. Sets. H. T. & J. Roche, Printers, 25, Hoxton-square, London. |