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ASTRONOMY.

on them at firt; between which power and force there is o exact an adjutment, that they continue in the ame tracks without any olid orbits to confine them.

, the nearet planet to the un, goes round him (as in a circle marked Plate XXXIX. fig. i.) in 87 days 23 hours of our lime nearly; which is the length of his year. But, being eldom een, and no pots appearing on his urface or dik, the time of his rotation on his axis, or the length of his days and nights, is as yet unknown. His ditance from the un is computed to be 32 millions of miles, and his diameter 2600. In his coure round the un, he moves at the rate of 95 thouand miles every hour. His light and heat from the un are almot even times as great as ours; and the un appears to him almot even times as large as to us. The great heat on this planet is no argument againt its being inhabited; ince the Almighty could as eaily uit the bodies and contitutions of its inhabitants to the heat of their dwelling, as he has done ours to the temperature, of our earth. And it is very probable that the people there have uch an opinion of us, as we have of the inhabitants of Jupiter and Saturn; namely, that we mut be intolerably cold, and have very little light at o great a ditance from the un.

This planet appears to us with all the various phaes of the moon, when viewed at different times by a good telecope; excepting only that he never appears quite full, becaue his enlightened ide is never turned directly towards us but when he is o near the un as to be lot to our ight in its beams. And, as his enlightened ide is always toward the un, it is plain that he hines not by any light of his own; for if he did, he would contantly appear round. That he moves about the un in an orbit within the earth’s orbit is alo plain, (as will be (hewn afterwards), becaue he is never een oppoite to the un, nor above 56 times the un’s breadth from his centre.

His orbit is inclined even degrees to the ecliptic; and that node from which he acends northward above the ecliptic is in the 14th degree of Taurus; the oppoite, in the 14th degree of Scorpio. The earth is in thee points on the 6th of November and 4th of May, new tyle; and when Mercury comes to either of his nodes at his inferior conjunction about thee times, he will appear to pas over the dik or face of the un, like a dark round pot; but in all other parts of his orbit his conjunctions are inviible, becaue he either goes above or below the un.

Mr Whiton has given us an account of everal periods at which Mercury may be een on the un’s dik, viz. in the year 1783, Nov. 12th, at 3 h. 44 m. in the afternoon ; 1786, May 4th, at 6 h. 57 m. in the forenoon; 1789, Dec. 6th, at 3 h. 55 min. in the afternoon; and 1799, May 7th, at 2 h. 34 in. in the afternoon. There will be everal intermediate tranits, but none of them viible to us.

, the next planet in order, is computed to be 59 millions of miles from the un ; and by moving at the rate of 69 thouand miles every hour in her orbit, (as in the circle marked ♀), he goes round the fun in 224 days 17 hours of our time nearly. But though this be the full length of her year, as he performs only 9$1/4$ revolutions on her own axis in that time, her year conits only of 9$1/4$ days; o that in her, every day and night together is as long as 24$1/3$ days and nights with us. This odd quarter of a day in every year makes every fourth year a leap-year to Venus; as the like does to our earth. Her diameter is 7906 miles; and by her diurnal motion the inhabitants about her equator are carried 43 miles every hour, beides the 69,000 above mentioned.

Her orbit includes that of Mercury within it; for at her greatet elongation, or apparent ditance from the un, he is 96 times his breadth from his centre; which is almot double of Mercury’s. Her orbit is included by the earth’s; for if it were not, he might be een as often in oppoition to the un, as he is in conjunction with him; but he was never een 90 degrees, or a fourth part of a circle, from the un.

When Venus appears wet of the fun, he ries before him in the morning, and is called the ; when he appears eat of the un, he hines in the evening after he ets, and is then called the ; being each in its turn for 290 days. It may perhaps be urpriing at firt, that Venus hould keep longer on the eat or wet of the un, than the whole time of her period round him. But the difficulty vanihes when we conider, that the earth is all the while going round the un the ame way, though not o quick as Venus; and therefore her relative motion to the earth mut in every period be as much lower than her abolute motion in her orbit, as the earth during that time advances forward in the ecliptic, which is 220 degrees. To us he appears, through a telecope, in all the various hapes of the moon.

The axis of Venus is inclined 75 degrees to the axis of her orbit; which is 51$1/2$ degrees more than our earth’s axis is inclined to the axis of the ecliptic; and therefore her eaons vary much more than ours do. The north pole of her axis inclines toward the 20th degree of a quarius, our earth’s to the beginning of Cancer; conequently the northern parts of Venus have ummer in the igns where thoe of our earth have winter, and vice vera.

The artificial day at each pole of Venus is as long as 112-y natural days on our earth.

The fun’s greatet declination on each ide of her equator amounts to 75 degrees; therefore her tropics are only 15 degrees from her poles, and her polar circles as far from her equator. Confequently, the tropics of Venus are between her polar circles and her poles; contrary to what thoe of our earth are.

As her annual revolution contains only 9$1/4$ of her days, the fun will always appear to go through a whole ign, or twelfth part of her orbit, in little more than three quarters of her natural day, or nearly in 18$3/4$ of our days and nights.

Becaue her day is o great a part of her year, the un changes his declination in one day o much, that if he paes vertically, or directly over head of any given place on the tropic, the next day he will be 26 degrees from