The Heavens: An Illustrated Handbook of Popular AstronomyR. Bentley, 1871 - 432 síður |
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angle aphelion appearance Arago astronomers atmosphere axis brightness brilliant celestial bodies celestial vault centre clouds clusters colour comets constellation craters dark described diameter dimensions disappear disk double stars Earth equator equatorial equinox extreme fact globe heat heavens hemisphere Herschel horizon hypothesis immense instruments intensity Jupiter Lastly length less light luminous points lunar Mädler Mars mass mean distance measure Mercury meridian meteors miles Milky minor planets Moon Moon's movement of rotation naked eye nearly nebula Neptune night nucleus observed orbit pass penumbra period phenomena photosphere physical constitution planet planetary poles portion position present proper motion rays regions remarkable revolution ring round the Sun satellites Saturn seen sidereal sidereal day solar day Solar System sometimes southern space sphere spots starry vault Sun's surface telescope terrestrial total eclipse traverse umbra Uranus variable variable stars varies velocity Venus whilst Zodiacal Light zone
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Síða 233 - We see it as Columbus saw America from the shores of Spain. Its movements have been felt, trembling along the far-reaching line of our analysis, with a certainty hardly inferior to that of ocular demonstration.
Síða 15 - Herschel has suggested, by the consideration that after all this improvement of our knowledge amounts to no more than a correction to an observed angle represented by the apparent breadth of a human hair viewed at the distance of about 125 feet.] • Before 1769, astronomers had endeavoured to determine the distance of the Sun in various ways.
Síða 173 - ... the most remote condition, of which we have positive evidence, was that of small, detached, melted globules, the formation of which cannot be explained in a satisfactory manner, except by supposing that their constituents were originally in the state of vapour, as they now exist in the atmosphere of the Sun ; and, on the temperature becoming lower, condensed into these
Síða 106 - As has been mentioned, the time shown by a sundial is called Apparent Solar Time. It differs from Mean Solar Time by an amount known as the Equation of Time, which is the total effect of two causes which make the length of the apparent solar day nonuniform. One cause of variation is that the orbit of the Earth is not a circle, but an ellipse, having the Sun at one focus. As a consequence, the angular speed of the Earth in its orbit is not constant; it is greatest at the beginning of January when...
Síða 187 - if their orbits are figured under the form of material rings, these rings will be found so entangled, that it would be possible, by means of one among them taken at hazard, to lift up all the rest...
Síða 140 - ... of controversy. In conclusion, this hypothesis suggests the probability that the other bodies belonging to our solar system have either already passed through a similar epoch, or are destined still to encounter it. With the exception of the polar ice of Mars we have hitherto obtained no certain glimpse into the thermal or meteorological condition of the planets : neither is the physical state of their surfaces accessible to our best telescopes. It is otherwise however with the moon, whose distance...
Síða 140 - Ehone glacier. These ridges are visible for the whole period during which that portion of the moon's surface is illuminated ; but it is only about the third day after the first quarter, and at the corresponding phase of the waning moon, when the sun's rays, falling nearly horizontally, throw the details...
Síða 97 - Astronomers, with a view of obtaining a convenient and uniform measure of time, have recourse to a mean solar day, the length of which is equal to the mean or average of all the apparent solar days in a year. An imaginary Sun, called the mean Sun...
Síða 396 - Instruction should proceed from the known to the unknown, from the simple to the complex, from concrete to abstract notions, from analysis to synthesis.
Síða 52 - These are the general grounds on which we suspect the sun to be the agent which causes magnetic disturbances ; but there is also some reason to believe that on one occasion our luminary was caught in the very act. On the 1st of September, 1859, two astronomers, Messrs. Carrington and Hodgson, were independently observing the sun's disc, which exhibited at that time a very...