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altitude angle apparent asteroids astronomical astronomical units atmosphere axis azimuth binary bright celestial equator celestial sphere centre chromosphere circle comet constellation corona declination density determined diameter disc Dist distance Double Stars earth earth's orbit earth's surface eccentricity eclipse equal equatorial eye-piece feet force globe gravity heat heavenly bodies horizon inches instrument Jupiter known latitude libration light longitude lunar lunar eclipse magnitude Mags mass mean measured meridian meridian circle meteoric method miles a second minutes moon moon's motion moving naked eye nearly nebulae node object object-glass observations parallax perihelion period perturbations photographs photosphere planet pole Pole-star probably proper motion radius right ascension ring rotation satellites seen shadow sidereal sidereal period Sirius solar spectra spectroscope spectrum stellar sun spots sun's synodic period telescope tides tion transit Uranus velocity Venus vernal equinox visible zenith
Сторінка 18 - ... is the great circle in which the plane of the earth's equator cuts the celestial sphere. It is often called the "Equinoctial.
Сторінка 178 - The radius vector of each planet describes equal areas in equal times. (3) The squares of the periods of the planets are proportional to the cubes of their mean distances from the su» ; ie, £12 : ia2 : : «!3 : a28. This is the so-called "Harmonic Law.
Сторінка 153 - From this, it is easily computed that the amount of heat received by the earth from the sun in a year is sufficient to melt a shell of ice 177.4 feet thick all over the earth's surface. 214. Solar Heat expressed as Energy. — Since according to the known value of the " mechanical equivalent of heat
Сторінка 401 - Power.—If we use the naked eye, we cannot see the image distinctly from a distance much less than a foot, but if we use a magnifying lens of, say, one inch focus, we can view it from a distance of only an inch, and it will look correspondingly larger. Without stopping to prove the principle, we may say that the magnifying power is simply equal to the quotient obtained by dividing the focal length of the object-glass by that of the eye-lens; or, as a formula M = — ; that is, — in the figure.
Сторінка 75 - Motion of the Pole of the Heavens around the Pole of the Ecliptic. — The obliquity of the ecliptic, which equals the angular distance of the pole of the heavens from the pole of the ecliptic, is not sensibly affected by precession.
Сторінка iv - The eminence of Professor Young as an original investigator in astronomy, a lecturer and writer on the subject, and an instructor in college classes, led the publishers to present the General Astronomy with the highest confidence; and this confidence has been fully justified by the event.