General AstronomyE Arnold & Company, 1923 - 392 oldal |
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absolute magnitude absorption altitude angle angular diameter apparent magnitude appear astronomical atmosphere axis binary body bright celestial sphere centre Cepheid Cepheid variables circle clusters comets components corresponding curve declination density determined direction disc displacement Earth Earth's atmosphere eccentricity equal equator equinox error galactic gravitation greater Greenwich increase instrument Jupiter known latitude light limb lines longitude lunar Mars mass maximum mean distance measured Mercury meridian meteors method micrometer miles Milky Moon Moon's nebula node novæ object-glass Observatory observed obtained occur orbit parallax parsecs perihelion period photographic planet Plate polar pole position proper motion radiation radius reflector relative right ascension ring rotation satellites Saturn seen sidereal sidereal period solar eclipse spectra spectral type spectroscopic spectroscopic binary spectrum spiral spots stars stellar Sun-spot Sun's supposed surface synodic period telescope temperature theory transit Uranus variables variation velocity Venus visual magnitudes whilst zenith
Népszerű szakaszok
73. oldal - RULES TO KNOW WHEN THE MOVEABLE FEASTS AND HOLYDAYS BEGIN. EASTER DAY, on which the rest depend, is always the First Sunday after the Full Moon which happens upon, or next after the Twenty-first Day of March ; and if the Full Moon happens upon a Sunday, Easter Day is the Sunday after.
109. oldal - ... the ratio of the velocity of the Earth in its orbit to the velocity of light, might not need correction or modification.
76. oldal - ... revolution on account of the various perturbing forces which may increase or decrease the interval by several hours. The period naturally associated with the Moon, however, is its period of revolution with regard to the Sun, since it is this period which controls the phases, A lunar month may be defined as the period from new Moon to new Moon, or from full Moon to full Moon, ie from conjunction to conjunction, or from opposition to opposition. This period is also known as the Synodic revolution....
29. oldal - Another atmospheric effect, for which it is necessary to make allowance in astronomical observations, is known as Refraction. When a ray of light passes from one medium into another of different density its direction is changed. If it passes from a less dense into a denser medium it is bent towards the normal to the interface between the two media ; conversely, if it is passing into a rarer medium it is bent away from the normal.
149. oldal - This is on the assumption that the diameter of the earth's shadow, at the distance of the moon, is 2^- times the diameter of the moon.
329. oldal - The radiation received from a plane surface varies as the cosine of the angle between the line of sight and the normal to the surface.
91. oldal - Does the Moon rotate on its axis as well as travel round the Earth ? This is a question which is easily answered, although the answer is sometimes found puzzling. Observation of the Moon with a low telescopic power, such as a pair of prismatic binoculars, will suffice to show the principal surface details. Continued observations will reveal that these markings are permanent, and that the Moon always turns the same face towards the Earth. This means that the Moon rotates on its axis in the same time...
70. oldal - England until the year 1752, when the difference between the two calendars had increased to 1 1 days. The day following September 2, 1752, was called September 14; at the same time, the beginning of the year was changed from March 25 to January 1 . In Russia the old style was adhered to until after the Revolution and the difference was then 13 days. It had become customary before the change for both dates to be used for commercial and scientific purposes. It may be noted that if a further modification...
242. oldal - They have likewise discovered two lesser Stars, or Satellites, which revolve about Mars; whereof the innermost is distant from the Center of the primary Planet exactly three of his Diameters and the outermost five; the former revolves in the Space of ten Hours, and the latter in Twenty-one and a Half...
164. oldal - ... refraction of glass, in common with other substances, being different for different colours. A single convergent lens will bring the blue rays to a focus nearer the lens than the red rays (Fig. 31). The difference in the refractive powers for any two chosen colours varies with the type of glass and it is therefore possible by combining two types of glass to make an achromatic lens, ie a lens in which any two chosen colours are brought to a common focus. By suitable choice of the curvatures of...