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Projections on the terminator of Mars and martian meteorology
Author(s) -
Douglass A. E.
Publication year - 1897
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.18971422205
Subject(s) - martian , mars exploration program , observatory , citation , meteorology , terminator (solar) , library science , history , astrobiology , computer science , astronomy , physics , ionosphere
Lastly : the relative visibility of some of the markings changes with their position with regard to the observer. For instance Somnus regio, which was almost invisible when in the centre of the disk, has grown more conspicuous as it has approached the limb. Anteros regio and Adonis regio have similarly become less salient on nearing the central meridian. Other markings under like conditions of position and illumination have not done so, but have remained as evident in the one aspect as in the other or, m Hermione regio, have been less conspicuous on nearing the limb. As of two markings occupying the same part of the disk, Hermione regio and Somnus regio for example, the one will change in one way, the other in an opposite manner, the changes cannot be a matter of obscuration. Secondly as the position of the markings has not shifted with regard to the Sun, the change cannot be intrinsic. It is due probably to a difference in the character of the rock or soil, greater or less roughness for example, in one region than in toe other. That in these markings we are looking down on a bare desert-like surface is what the observations imply. Nov. 7 4h 34m-40m, Nov. ·9 oh 32m-43m stehen den Lesern zur Einsicht zur Verfligung. The librations affecting Venus and Mercury are of two kinds: true libration, due to the planet's own motion; and apparent libration, due to the motion of the observer ~~st kind alone can affect the amount of visible surface presented to him since only libration with regard to the Sun can produce any alteration in the parts of the planet's surface under illumination. True libration may take place either in longitude or latitude; the former depending upon the eccentricity of the planet's orbit, the latter upon the inclination of the pole of rotation to that orbital plane. The amount of the latter we do not yet know exactly; but from the fact that observations here show no perceptible deviation from what would be the case were the pole perpendicular to the orbital plane, any possible inclination must be small. The libration in longitude is a perfectly definite quantity and amounts in the case of Venus at its maximu~, to 4 7' of arc ; in Lowell Observatory, I 896 Oct. 2 I. the case of Mercury to 23° 39'. This is the extreme limit …