The Heavens Above: A Popular Handbook of Astronomy

Here, then, we obtain a first notion of the rotundity of the earth, since a sphere is the only body which is presented always to us under the form of a circle, from whatever poi...

86. _Cause of Precession._--We have seen that the earth is flattened at the poles: in other words, the earth has the form of a sphere, with a protuberant ring around its equator...

288. _The Tails of Comets._--The _tails_ of brilliant comets are rapidly formed as the comet approaches the sun, their increase in length often being at the rate of several mill...

267. _Physical Constitution of Saturn._--The physical constitution of Saturn seems to resemble that of Jupiter; but, being twice as far away, the planet cannot be so well studie...

The bright-lined spectra of several substances are given in the frontispiece. The number of lines in the spectra of the elements varies greatly. The spectrum of sodium is one of...

14. _Declination and Right Ascension._--The _declination_ of a heavenly body is its distance north or south of the celestial equator. The _polar distance_ of a heavenly body is...

307. _Aerolites._--There is no certain evidence that any deposit from ordinary shooting-stars ever reaches the surface of the earth; though a peculiar dust has been found in cer...

The farther the earth is from the sun, the less rapidly does its shadow taper, and therefore the greater its diameter at the distance of the moon; and, the nearer the moon to th...

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Since celestial longitude and right ascension are both measured from the first point of Aries, the longitude and right ascension of the stars are slowly changing from year to ye...

238. _The Volume and Density of Mars._--Among the larger planets Mars is next in size to Mercury. Its real diameter is somewhat more than four thousand miles, and its bulk is ab...

116. _Lunar Craters._--The smaller saucer-shaped formations on the surface of the moon are called _craters_. They are of all sizes, from a mile to a hundred and fifty miles in d...

The least retardations for full moon occur when the moon is near the vernal equinox at full: the sun must then be near the autumnal equinox. Hence the least retardations for ful...

The distortions of the solar lines indicate that the wind at the surface of the sun often blows with a velocity of _from one hundred to three hundred miles a second_. The most v...

377. _The Great Nebula of Andromeda._--This is one of the few nebulæ that are visible to the naked eye. We see at a glance that it is not a star, but a mass of diffused light. I...

76. _Diurnal Inequality of Tides._--The height of the tide at a given place is influenced by the declination of the moon. When the moon has no declination, the highest tides sho...

Although the mass of the sun is over three hundred thousand times that of the earth, the pull of gravity at the surface of the sun is only about twenty-eight times as great as a...

At times, also, the spectrum of a spot indicates violent motion in the overlying gases by distortion and displacement of the lines. This phenomenon occurs oftener at points near...

350. _Physically Double and Multiple Stars._--In the majority of cases the components of double and multiple stars are in reality comparatively near together, and are bound toge...

2-1/2 stars of the 2d magnitude to make one of the 1st. 6 stars of the 3d magnitude to make one of the 1st. 16 stars of the 4th magnitude to make one of the 1st. 40 stars of the...

Comet, Biela's, 293. and earth, collision of, 316. Coggia's, 297. Donati's, 296. Encke's, 293. Halley's, 291. of 1680, 290. of 1811, 290. of 1843, 295. of 1861, 297. of June, 18...