THE PLANETS URANUS AND NEPTUNE. 403
of rotation always parallel to itself and in the plane of theecliptic; so that the axis in question would pass through theSun at the solstices, while the Sun ’s distance from a pole ofthe heavens would change from zero at a solstice to 90° at anequinox. Upon this supposition, figures may easily he drawn,similar to those used for the Earth in the earlier part ofLecture VIII., which would indicate the Sun ’s daily path forvarious seasons and localities.
In such a case it can also he shown, if the satellites movedin the plane of the equator of Uranus , that they wouldappear, when seen from any place upon the planet, to describea daily path in the sky which would always intersect thehorizon in its east and west points. If an observer were uponthe equator, they would pass through his zenith at mid-day;if he were near to a pole, they would all the day long keepclose to his horizon; while they would cross his meridian atan intermediate elevation for intermediate places of observa-tion. All this can be readily concluded from the fact thatthey would constantly be 90° from either pole of the heavens,the altitude of which above the horizon of any place, as in thecase of the Earth (see Lecture VIII., p. 180), would be equal tothe observer’s latitude.
Let us, however, next consider what appearance they wouldpresent to an observer upon the Earth , if they thus rotatedround Uranus in a plane at right angles to the ecliptic. It isevident that, if at any time that plane were turned edge-wise to our view, they would seem simply to travel up anddown in straight lines perpendicular to the ecliptic, passingalternately before and behind the planet. On the other hand,if that plane should at any time he at right angles to ourview, they would seem to go round the planet in circles. Atintermediate times their paths would appear as ellipses of agreater or less degree of ovalness. But in every case theirmotion would be in a plane whose direction would be to thenorth and south of the ecliptic, and always perpendicular toit. They would not have any motion at all round Uranus from east to west, or from west to east, relatively to theecliptic.