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Updated: May 13, 2025
The great majority of cometary orbits are classed as parabolic; and it is ordinarily inferred that they are visitors from remote space, and will never return. But are they rightly classed as parabolic? Observations on a comet moving in an extremely eccentric ellipse, which are possible only when it is comparatively near perihelion, must fail to distinguish its orbit from a parabola.
Sept. 30, '82, 4.30 A.M. I am down in Camden county, New Jersey, at the farmhouse of the Staffords have been looking a long while at the comet have in my time seen longer-tail'd ones, but never one so pronounc'd in cometary character, and so spectral-fierce so like some great, pale, living monster of the air or sea.
Discarding the crude notions of cometary impact and volcanic eruption, Laplace filled up the gaps in the hypothesis with the aid of well-known laws of gravitation and motion.
The return of Halley's comet in 1835 was looked forward to as an opportunity for testing the truth of floating cometary theories, and did not altogether disappoint expectation. As early as 1817, its movements and disturbances since 1759 were proposed by the Turin Academy of Sciences as the subject of a prize ultimately awarded to Baron Damoiseau.
Nebulae are vast cometary clouds, with particles more or less widely separated, giving off gases through meteoric collisions, internal or external, and perhaps glowing also with electrical or phosphorescent light. Gravity eventually brings the nebular particles into closer aggregations, and increased collisions finally vaporize the entire mass, forming planetary nebulae and gaseous stars.
These, by the character of their movements, serve as a link between the planetary and cometary worlds, and by the nature of their construction, seem to mark a stage in cometary decay.
The outline which would bound my walks would be, not a circle, but a parabola, or rather like one of those cometary orbits which have been thought to be non-returning curves, in this case opening westward, in which my house occupies the place of the sun.
Suppose we take off from here, dive at Earth, make a near-graze, and let its gravity curve our course! Like a cometary path! That's what we've got to do!" He kicked off his magnetic-soled shoes and went diving down to the airlock. Over his shoulder he panted an order for the radar-duty man to relay anything from Earth down to him there.
Between the brilliant circular semi-ring and the head, the cometary substance appeared to be dark, of great rarity, and very diaphanous. "The luminous self-ring floated: one day it seemed to be suspended in the diaphanous atmosphere by which the head of the comet was surrounded, at a distance of 322,000 English miles from the nucleus. "This distance was not constant.
But as the nucleus faded towards the end of June, they came out strongly, and were more and more clearly seen, both at Greenwich and at Princeton, to agree, not with the spectrum of hydro-carbons glowing in a vacuum tube, but with that of the same substances burning in a Bunsen flame. It need not, however, be inferred that cometary materials are really in a state of combustion.
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