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Stars and Planets

Stars shine entirely by their own light; planets shine chiefly, if not entirely, by reflected light. Stars are suns, globes of glowing flame, the planets reflect the light of the sun. Not more than 3000 stars are ever visible to the naked eye on a clear night. Round the whole earth man can with unaided eye see 5000 to 6000. Sir William Herschel calculated roughly the number of stars within reach of his powerful telescope, round the whole earth, to be 20,000,000-twenty millions of burning suns. Stars are commonly classed according to "magnitude," which really means "brightness," the degree of brightness fixing the class of a star. Stars can be seen without a telescope as low down as the 6th magnitude. Of Ist magnitude stars there are altogether about 20; 2nd magnitude, 65; 3rd magnitude, 200, and so on, till those of the 6th magnitude number over 2000. Alpha Centauri is the nearest star whose distance has been measured; it is 20,475,000,000,000 miles from the earth! 61 Cygni is 45,500,000,000,000 miles away, and Sirius is nearly 91,000,000,000,000 miles distant. Others are further still. Light travels 188,000 miles in a single second of time. A ray from the sun reaches the earth in 8½ minutes; each light gleam that reaches the eye of man from Alpha Centauri left that star 3/2 years before! During all that time it had flashed ceaselessly onward, 188,000 miles each second. The light from 61 Cygni takes 714 years, that from Sirius takes 20 years to reach the earth.

The earlier Zodiac has been ascribed to the Egyptians and to the Hindoos. No other people would be likely to confer a sign on water (aquarius), and it would be made to accord with the flood or fall of the Nile or the Ganges. It would then be appropriately followed by "Pisces."

Democritus, a Greek, taught that the Milky Way was composed of innumerable stars. The Phoenicians sailed by the stars in Great and Little Bear. The precision of Astronomy arises not from theories, but from prolonged observation, and the regularity of the mean motions, and the ascertained uniformity of their irregularities. Ephemerides of the planets, places of eclipses, etc., have been published for 300 years, and were at first nearly as precise as they are to-day. A general conjunction of the planets can only occur in 17 billions of years. The next transit of Venus will occur in A. D. 2004.

A circle, whose diameter is a million of miles, has nearly 5 miles in every second of its periphery, and 291 miles in every minute of its periphering. Then, as a minute is to the least visual angle by the average of eyes, so at the distance of a million of miles, any object less than 291 miles in diameter is invisible. But if a telescope with light and power of 500 is used, then the eye sees equal to 500 minutes, and shows an object, or the 0.58 of a mile.

What is called the tail of a comet is a luminous projection in a line directly opposite to the Sun, which, therefore, follows them as they approach the Sun and goes before them as they leave the Sun, and is a head or tail as their positions vary. The comet 0. 1811 was 10,900 miles in diameter-twice the bulk of the earth -and its luminous projection was 132 millions of miles. The comet which returned in October 1835 was very bright, and of a gold color. It was the same in 1531, it was dark and leaden in 1607, bright in 1682, and dark and obscure in 1759.

The Sun's spots cross the Sun from East to West, and show that the axis is inclined 3° 45' to the Eastward. Spots have been seen to divide and separate in many parts. When they disappear, they are succeeded by faculæ or bright spots. They are classed as openings, shallows, ridges, nodules, corrugations, indentations, and pores. A spot completes its revolution in about 27 days.

The coldness of the Moon's light is known. The heating rays are supposed to be absorbed.

The surface of the Moon shows what seem to be hundreds of volcanoes. The Earth's shadow is from 800,000 to more than a million of miles. The Moon's shadow extends from 225 to 240,000 miles, and, therefore, does not always reach the Earth. The breadth of the Earth's shadow at the Moon is about 3 times the Moon's diameter.