. The children's book of stars . e about the same as they do here. Herorbit is nearly a circle, so that her distance fromthe sun does not vary much, and the heat will notbe much greater from this cause at one time of theyear than another. As her orbit is tilted up a little she does notpass between us and the sun at each revolution, butoccasionally she does so, and this passing is calleda transit. Many important facts have been learnedby watching these transits. Mercury also hastransits across the sun, but as he is so muchsmaller than Venus they are not of such greatimportance. It was by the cl
. The children's book of stars . e about the same as they do here. Herorbit is nearly a circle, so that her distance fromthe sun does not vary much, and the heat will notbe much greater from this cause at one time of theyear than another. As her orbit is tilted up a little she does notpass between us and the sun at each revolution, butoccasionally she does so, and this passing is calleda transit. Many important facts have been learnedby watching these transits. Mercury also hastransits across the sun, but as he is so muchsmaller than Venus they are not of such greatimportance. It was by the close observation ofVenus during her transits that the distance fromthe earth to the sun was first measured. Not untilthe year 2004 will another transit of Venus occur. It is not difficult to imagine that the earth mustappear a splendid spectacle from Venus, whence FOUR SMALL WORLDS 55 she is seen to great advantage. When nearest tous she must see us hke a little moon, with markingsas the continents and seas rotate, and these will. ORBITS OF UAKS, THE EARTH, VENUS, AND MERCURY. change as they are obscured by the clouds rollingover them. At the North and South Poles will beglittering ice-caps, growing larger and smaller as 56 THE CHILDRENS BOOK OF STARS they turn toward or away from the sun. A briUiantspectacle ! We might say with a sigh, If only we could seesuch a world ! Well, we can see a world—notindeed, so large as Venus, yet a world that comesalmost as near to us as Venus does, and which,unlike her, is outside us in order from the sun, sothat when it is nearest to us the full sunlight ison it. This is Mars, our neighbour on the otherside, and of all the fascinating objects in thesky Mars is the most fascinating, for there, if any-where, should we be likely to discover beings likeourselves! Mars takes rather more than half an hour longerto rotate than we do, and as he is so much smallerthan the earth, this means that he moves roundmore slowly. His axis is tilted at nearly t
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