George F. Chambers

“ It is not too much to say that the generality of people regard the tail of a comet as the comet; and that though an object may be a true comet from an astronomer’s point of view, yet if it has no tail its claims go for nought with the mass of mankind. ”

“ We now come to the best known planet of the solar system, reckoning outwards from the Sun, and though this planet itself, as an object to look at, has no particular interest for the general public, yet the history of its discovery is a matter of extreme interest. ”

“ The Earth is an ordinary planet member of the solar system, amenable to the same laws, impelled by the same forces, and going through the same movements as the other members of the Sun’s entourage. Yet, by reason of the fact that we are ourselves on the Earth and are not spectators of it looking at it from at a distance, there are many phenomena coming under our notice which require special treatment, and it is often very difficult to say where the province of the astronomer ends and that of the geographer begins. ”

“ The planet Venus has two things in common with Mercury. One is, that being an inferior planet, that is to say, a planet revolving round the Sun in an orbit within that of the Earth, it is never very far distant from the Sun, and therefore can never be seen on a distinctly dark sky. The second point alluded to arises out of the first; Venus exhibits from time to time a series of phases which are identical in character with those of Mercury, and therefore with those of the Moon. Venus differs, however, from Mercury in the very important point of size. ”

“ From Uranus Saturn can be seen, and perhaps Jupiter, both as inferior planets, just as we see Venus and Mercury; but all the other inner planets, including Mars and the Earth, would be hopelessly lost to view, because perpetually too close to the Sun. Possibly, however, they might, on rare occasions, be seen in transit across the Sun’s disc. Neptune, of course, would be visible and be the only superior planet. The Sun itself would appear to an observer on Uranus as a very bright star, with a disc of 13⁄4′ of arc in diameter. ”

“ Twilight is another phenomenon associated with astronomical principles and effects which depends in some degree on the Earth’s atmosphere and on the laws which regulate the reflection and refraction of light. After the Sun has set it continues to illuminate the clouds and upper strata of the air just as it may often be seen shining on the tops of hills long after it has disappeared from the view of the inhabitants of the 81 plains below, and indeed may illuminate the chimneys of a house when it is no longer visible to a person standing in the garden below. ”

“ Sun-spots may come and go; bright planets may shine more brightly; the Sun or Moon may be obscured by eclipses; temporary stars may burst forth,—all these things are within the ken of the general public by means of newspapers or almanacs, but it is a comet which evokes more questionings and conversations than all the other matters just referred to put together. When a new and bright comet appears, or even when any comet not very bright gets talked about, the old question is still fresh and verdant—“Is there any danger to the Earth to be apprehended from collision with a Comet?” ”

“ A superior planet is not, as it were, chained to the Sun so as to be unable to escape beyond the limits of morning or evening twilight; it may have any angular distance from the Sun up to 180°, reaching which point it approaches the Sun on the opposite side, step by step, until it again comes into conjunction with the Sun. As applied to a superior planet, the term “conjunction” means the absolute moment when the Earth and the Sun and the planet are in the same straight line, the Sun being in the middle. ”

“ Although we all of us now perfectly understand that the Earth is a planet moving round the Sun as a centre, it is, comparatively speaking, but recently that this fact has become generally recognised and understood. ”

“ He considered, in effect, that the blaze of the Sun’s light was a lesser evil than the tremors inseparable from observations of the planet, clear it might be in some degree of inconvenient Sun-light, but viewed through the vapours and atmospheric disturbances, which always spoil all observations near the horizon. Schiaparelli’s observations yielded various results, most of them novel, and one of them very startling. He considers Mercury to be a much spotted globe and to be enveloped in a tolerably dense atmosphere. ”

“ The fact that as a comet approaches the Sun some forces, no doubt of solar origin, come into operation to vaporise and therefore expand the matter composing the comet is sufficiently shown by the great developement which takes place as we have seen in the tails of comets, but in regard to the heads of comets we are face to face with a strange enigma. Though the tails expand the heads contract as the comet approaches its position of greatest proximity to the Sun. ”

“ A periodicity so well established would naturally invite astronomers to seek the causes which produced it. The presence of spots only in the Zodiacal regions led Galileo to suspect the existence of some relation between the spots and the position of the planets; but there is in this a mere surmise, which, when it was made, had nothing to justify it, and it is still impossible for us to say anything for certain on the point. The determining cause of the periodicity may exist in the interior of the Sun, and may depend on circumstances which will for ever remain unknown to us. ”

“ As soon as the Sun has disappeared below the horizon all the clouds overhead continue for a few minutes so highly illuminated as to reflect scarcely less light than the direct light of the Sun. As, however, the Sun gradually sinks lower and lower, less and less of the visible atmosphere receives any portion of its light, and consequently less and less is reflected minute by minute to the Earth at the observer’s station until at length the time comes when there is no sunlight to be reflected—and it is night. ”

“ Considered as a system, the rings are distinctly more luminous than the planet, and of the two bright rings, the inner one is brighter than the outer one; and the inner one is less bright at its inner edge than elsewhere. It is also to be noticed that when seen edgeways just about the time of the Saturnian equinoxes, when the Sun is shifting over from one side of the ring to the other, and the ring is dwindling down to a narrow streak, its edges (forming the ansæ as they are termed) do not disappear and reappear at the same time, and are not always of the same apparent extent. ”

“ The Sun is a sphere, and is surrounded by an extensive but attenuated envelope, or rather series of envelopes, which taken together bear some analogy to the atmosphere surrounding the Earth. These envelopes, which we shall have to consider more in detail presently, throw out rays of light and heat to the confines of the Solar System, though as to the conditions and circumstances under which that light and heat are generated we are entirely ignorant. ”

“ There is certainly no one body in creation which is so emphatically pre-eminent as the Sun. Whether or no there are stars which are suns—centres of systems serving in their degree the purposes served by our Sun, I need not now pause to enquire, though I think the idea is a very probable one; but of those celestial objects with which our Earth has a direct relationship, beyond doubt the Sun is unquestionably entitled to the foremost place. It is, as it were, the pivot on 19 which the Earth and all the various bodies comprising the Solar System revolve in their annual progress. ”

“ It is impossible therefore to entertain the least doubt as to the truth of the theory that the spots are excavations in the luminous stratum which envelopes the whole of the solar globe.
If it be true that a spot is a cavity, it follows that when it reaches the margin of the solar disc we ought to detect a hollow place; and this will be so much the more easy to observe according as the cavity is larger and deeper. As a matter of fact, numerous observations of this sort have been recorded from the time of Cassini down to the present time under the designation of “notches” on the Sun’s limb. ”

“ Next beyond Jupiter, proceeding outwards from the Sun, we reach the planet Saturn, which beyond any doubt is the most beautiful and most interesting of all the planets. Nobody who has ever had a fairly good chance of seeing it can have the least doubt that this is the case. ”

“ If Saturn has any inhabitants at all constituted like ourselves, which is highly improbable, they will have a chance of seeing celestial phenomena of the greatest interest. What with the rings surrounding the planet and 8 moons in constant motion, there will be an endless succession of astronomical sights for them to study. The amount of light received from the Sun cannot be much—barely 1/100th what the earth receives. The ring and satellites will therefore be useful as supplementary sources of light ”

“ Not only is the Earth’s orbit eccentric in form, but its eccentricity varies within narrow limits; and besides this the orbit itself, as a whole, is subject to a periodical shift of place, from the joint effect of all which changes it comes about that our seasons are now of unequal length, the spring and summer quarters of the year unitedly extending to 186 days, whilst the autumn and winter quarters comprise only 178 days. The sun therefore has the chance of shining for a longer absolute period of time over the northern hemisphere than over the southern hemisphere ”

“ Careful scrutiny with a powerful eye-piece reveals the fact that the Sun’s surface is marked by a multitude of wrinkles and irregularities which it is well-nigh impossible to describe in words. More or less everywhere there is a general mottling visible; it is more distinct in some places than others, and especially so towards the centre of the disc. This peculiar appearance varies very much from time to time, and its distinctness seems to depend a great deal on the state of the Earth’s atmosphere, for it becomes invisible when the air is disturbed ”

“ Twilight is usually reckoned to last until the Sun has sunk 18° below the horizon, but the question of its duration depends on where the observer is stationed, on the season of the year, and (in a slight degree) on the condition of the atmosphere. The general rule is that the twilight is least in the tropics and increases as the observer moves away from the equator towards either pole. Whilst in the tropics a depression of 16° or 17° is sufficient to put an end to the phenomenon, in the latitude of England a depression of from 17° to 20° is required. ”

“ But what are we to say to Schiaparelli’s conclusions that these markings are so nearly permanent, taking one day with another, that Mercury’s rotation cannot be measured in hours at all, but is a matter of days,—in point of fact, of 88 days; and that in reality Mercury occupies in its rotation on its axis the whole of the 88 days which constitute its sidereal year, or period of revolution round the Sun. The counterpart of this for us would be that, instead of the inhabitants of the earth having a day of 24 hours, they would have only one day and night every 365 days. ”

“ Mercury and Venus, in regard to their orbital motions, stand very much on the 16 same footing with respect to the inhabitants of the Earth as the Moon does, and accordingly both those planets in their periodical circuits round the Sun exhibit the same succession of phases as the Moon does. In the case, however, of the superior planets things are otherwise. Two only of them, Mars and Jupiter, are sufficiently near the Earth to exhibit any phase at all. When they are in quadrature (i. e., 90° from the Sun on either side) there is a slight loss of light to be noticed along one limb. ”

“ Half a century ago the actual state of our knowledge respecting the Sun might without difficulty be brought within the compass of a single chapter in any book on Astronomy, but so enormous has been the development of knowledge respecting the Sun of late years, that it is no longer a question of getting the materials properly into one chapter, but it is a matter of a whole volume being devoted to the Sun, or even, as in the case of Secchi, of two large octavo volumes of 500 pages each being required to cover the whole ground exhaustively. ”

“ It is obvious from the foregoing that we on the Earth need not concern ourselves very much about lunar heat; and I will only add that F. W. Very, by an ingenious endeavour to localise the Moon’s radiant heat, has been able, he thinks, to establish the fact that on the part of the Moon to which the Sun is setting, what he calls the heat-gradient (using a phrase suggested by terrestrial meteorology) appears to be steeper than on that part to which the Sun is rising. Generally, Very’s observations accord fairly with Lord Rosse’s. ”

“ There is often a slight general resemblance between a planet and a comet, as regards the path which each class of body pursues. Probably the least reflective person likely to be following me here understands the bare fact, that all the planets revolve round the Sun, and are held to defined orbits by the Sun’s influence, or attraction, as it is called. ”