There are a variety of formation mechanisms for the different types of nebulae. Some nebulae form from gas that is already in the interstellar medium while others are produced by stars. Examples of the former case are giant molecular clouds, the coldest, densest phase of interstellar gas, which can form by the cooling and condensation of more diffuse gas.
Before studying the effects that the motions of the stars have had and will have upon the constellations, it is worth while to consider a little further the importance of the stellar pictures as archives of history. To emphasize the importance of these effects it is only necessary to recall that the constellations register the oldest traditions of our race. A knowledge has been obtained of their height above the ground during their flight and of the length of their visible courses.
Would a huge runaway sun, like Arcturus, for instance, make such an opening if it should pass like a projectile through the Milky Way?
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The fall of meteorites offers an appreciable, though numerically insignificant, peril to the inhabitants of the earth. Historical records show perhaps three or four instances of people being killed by these bodies. But for the protection afforded by the atmosphere, which acts as a very effective shield, the danger would doubtless be very much greater.
It has been calculated that on a clear night the total starlight from the entire celestial sphere amounts to one-sixtieth of the light of the full moon; but of this less than one-twenty-fifth is due to stars separately distinguished by the eye. If there were no obscuring medium in space, it is probable that the amount of starlight would be noticeably and perhaps enormously increased.
It is a singular fact that recent investigations seem to have proved that an event of this kind actually happened in North America — perhaps not longer than a thousand or two thousand years ago.
– William A. Miller
This leads us back again to the wonderful group of the Pleiades. All of the principle stars composing that group are traveling in virtually parallel lines. Whatever force set them going evidently acted upon all alike.
At the surface such a body is enveloped in a shell of relatively cool matter. Now suppose a great attracting body, such as another sun, to approach near enough for the difference in its attraction on the two opposite sides of the body and on its center to become very great the consequence will be a tidal deformation of the whole body, and it will lengthen out along the line of the gravitational pull and draw in at the sides
But serious questions remain. It needs, for instance, but a glance at the Triangulum monster to convince the observer that it cannot be a solar system which is being evolved there, but rather a swarm of stars. Many of the detached masses are too vast to admit of the supposition that they are to be transformed into planets, in our sense of planets, and the distances of the stars which appear to have been originally ejected from the focal masses are too great to allow us to liken the assemblage that they form to a solar system.
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To most minds mystery is more fascinating than science. But when science itself leads straight up to the borders of mystery and there comes to a dead stop, saying, At present I can no longer see my way, the force of the charm is redoubled.
It was another of the magical wonders of the unknown South, and as such it formed the basis of many a wild surmise and many a sea-dog’s yarn. Scientific investigation has not diminished its prestige, and today no traveler in the southern hemisphere is indifferent to its fascinating strangeness.
To most minds mystery is more fascinating than science. But when science itself leads straight up to the borders of mystery and there comes to a dead stop, saying, At present I can no longer see my way, the force of the charm is redoubled.
The name, coal-sacks, given to these strange voids is hardly descriptive. Rather they produce upon the mind the effect of blank windows in a lonely house on a pitch-dark night, which, when looked at from the brilliant interior, become appalling in their rayless murk.
The name, coal-sacks, given to these strange voids is hardly descriptive. Rather they produce upon the mind the effect of blank windows in a lonely house on a pitch-dark night, which, when looked at from the brilliant interior, become appalling in their rayless murk.
One of Barnard’s earliest and most excellent photographs includes two of them, both in the star-cluster M8. The larger, which is roughly rectangular in outline, contains one little star, and its smaller neighbor is lune-shaped — surely a most singular form for such an object.
Splendid and astonishing, however, as this remarkable phenomenon really was, and although it could not fail to call forth the admiration and applause of every beholder, yet I must confess that there was at the same time something in its singular and wonderful appearance that was appalling.
It is not alone the conspicuousness of this celestial vacancy, opening suddenly in the midst of one of the richest parts of the Galaxy, that has given it its fame, but quite as much the superstitious awe with which it was regarded by the early explorers of the South Seas.
There remains the question of the luminiferous ether by whose agency the waves of light are borne through space. The ether is as mysterious as gravitation. With regard to ether we only infer its existence from the effects which we ascribe to it.
The most famous of the coal-sacks, and the first to be brought to general attention before astronomers had awakened to the significance of such things, lies adjacent to the Southern Cross, and is truly an amazing phenomenon.