A primary astronomy .. . ear the plane of his equator, theymust also be near the ecliptic. 587. How do these Satellites TELESCOPIC VIEWS OF THE MOONSOF JUPITER. usually appear to be situated ? At different distances;some on one side of theprimary, and some on theother. 588. What is their apparentmotion 1 They seem to oscillatelike a pendulum, from theirgreatest elongation on oneside, to their greatest elon-gation on the other. [If we could look down perpendicularly upon the ecliptic, we should see these satel-lites revolving in apparent circles ; but as wo are in or near the plane of the eclip
A primary astronomy .. . ear the plane of his equator, theymust also be near the ecliptic. 587. How do these Satellites TELESCOPIC VIEWS OF THE MOONSOF JUPITER. usually appear to be situated ? At different distances;some on one side of theprimary, and some on theother. 588. What is their apparentmotion 1 They seem to oscillatelike a pendulum, from theirgreatest elongation on oneside, to their greatest elon-gation on the other. [If we could look down perpendicularly upon the ecliptic, we should see these satel-lites revolving in apparent circles ; but as wo are in or near the plane of the ecliptic,which is the plane of their orbit, they seem merely to pass to and from the plane.] 589. What is the Form of the Orbits of these Satellites ?They are very nearly circular. [This fact is ascertained by observing that their greatest elongalion is nearly thei same both east and west at every revolution; whereas, if their orbits were very ellip-I tical, their greatest elongations would vary. See Question 247, and Notes.]. PEEMAEY ASTEONOMY. 125 590. In what direction do they revolve ? From east to west, or in the direction their primaryrevolves, both upon his axis and in his orbit. [See the directions as indicated by the arrows in the next cut.] 591. Have they a revolution around their respective Axes ? They are supposed to revolve once upon their axesduring every revolution around their primary, as is thecase with our own satellite. 592. Are Jupiters Moons always visible ? They are not. Sometimes only one or two can beseen. (See the lower figure in the opposite cut.) 593. Why is this ? Because, as their orbits lie near the plane of Jupitersorbit, they have to pass his broad shadow, and betotally eclipsed at every revolution. eclipses of jupiters • v*D \r. KC CO! OA
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
