It was discovered on the first of January 1805, that the ascending node of the planet Herschel was in twelve degrees and fifty-three minutes of the sign Gemini, and advances 16 seconds in a year. Saturn in twenty-one degrees and 59 minutes of Cancer, and advances 32 seconds in a year. Jupiter in 8 degrees and 27 minutes of Cancer, and advances 36 seconds yearly. Mars in 18 degrees, and four minutes of Taurus, and advances 28 seconds yearly. Venus in 14 degrees and 55 minutes of Gemini, and advances 36 seconds yearly. Mercury in 16 degrees of Taurus, and advances 43 seconds every year. In these observations, the earth's orbit is considered the standard, and the orbits of all the other planets obliquely to it. The nearest planet to the sun is Mercury. The great brilliancy of light emitted by this planet: the shortness of the period during which observations can be made upon his disk; and his position among the vapors of the horizon when he is observed, have hitherto prevented Astronomers, from making interesting discoveries to be relied on with certainty respecting this planet. This planet, when viewed at different times with a good telescope, appears in all the various shapes of the Moon, which is a plain proof that he receives, (like the Moon,) all his light from the Sun. That he moves round the Sun in an orbit, within the orbit of the earth, is also plain; because he is never seen opposite to the Sun, nor above 56 times the Sun's diameter from his centre. It has been said by Authors, that his light and heat from the Sun must be almost seven times as great as our's ; judging from his nearness to it. His light and heat however, depend more on the height and density of his atmosphere, than to his near approach to that luminary. His distance from the Sun is computed at 73,000,000 of miles, is 3,225 in diameter, and performs a revolution round the Sun, in 87 days 23 hours 15 minutes and 28 seconds: his apparent diameter as seen from the earth, is ten seconds. His orbit is inclined,7 degrees to the ecliptic; and that node from which he ascends northward above it, is in the 16th degree of Taurus, the opposite in the 16th degree of Scorpio. The earth is in these points on the 6th of November, and 4th of May; when he comes to either of his nodes at his inferior conjunction about these times, he will appear to pass over the face of the sun like a dark round spot.But in all other parts of his orbit, his conjunctions are invisible; because he either goes above or below the Sun. On the 5th day of May, at 6 hours 43 minutes 22 seconds in the morning, in the year 1832, in the longitude of Washington, he was in conjunction with the Sun. His next visible conjunction will be on the 7th day of November 1835. Venus, the next planet in order is 68,000,000 of miles from the Sun by computation, and by moving at the rate of 69,000 miles every hour in her orbit, she performs her revolution round the Sun in 224 days, 16 hours and 49 minutes of our time; in which, (though it be the full length of her year,) she has only 9 days and a quarter, according to observations made by Bi anchini; so that her every day and night together, is as long as 348 days and nights with us. This odd quarter of a day in every year, makes in every fourth year a leap year to Venus, as the like does to the earth which we inhabit. Her diameter is computed at 7687 miles, and performs her diurnal revolutions in 23 hours 20 minutes, and 54 seconds; with an inclination of her orbit to the ecliptic, of 3 degrees 23 minutes, and 35 seconds. Her orbit includes the orbit of Mercury within it, for at her greatest elongation, or apparent distance from the Sun, she is about 96 times his diameter from his centre; while that of Mercury is not above 56. Her orbit is included within the orbit of the earth, for if it were not, she would be as often seen in opposition as in conjunction with the Sun. But she never departs from the Sun to exceed 47 degrees, and that of Mercury 28, it is therefore certain that the orbit of Mercury is within the orbit of Venus, and that of Venus within the orbit of the earth. When this planet is west of the Sun, she rises in the morning before him, and hence she is called the morning star; and when she sets after the Sun, she is called the evening star; so that in one part of her orbit she rides foremost in the procession of night, and in the other, anticipates the dawn; being each in its turn 290 days. The axis of Venus is inclined 75 degrees to the axis of her orbit, which is 51 degrees and 32 minutes more than the axis of the earth is inclined to the axis of the ecliptic; and therefore her seasons vary much more than our's. The north pole of her axis, inclines towards the 20th degree of Aquarius; the earth's to the beginning of Cancer. Consequently the northern parts of Venus have Summer, in the signs where those of the earth have Winter, and vice versa. The orbit of Venus is inclined three and one half degrees to the earth's, and crosses it in the 14th degree of Gemini, and Sagittarius, and therefore when the earth is near the points of the ecliptic, at the time when Venus is in her inferior conjunction,* she appears like a spot on the Sun, and it furnishes a true method of calculating the distances of all the planets from the Sun. It will not be uninteresting to those who peruse this treatise, to be put in the possession of all the elements of the transits, both of Mercury and Venus over the Sun's disk; from this period to the end of the present century, I therefore insert the following tables :— TRANSIT OF MERCURY OVER THE SUN'S DISK. * Inferior conjunction is, when the planet is between the earth and the Sun, in the nearest part of its orbit. |