The Children's Book of Stars

ouring out far greater heat and light than anything that we have here, even in the tropics. It was at first supposed that Mercury must have an extra thick covering of clouds to protect him

er than in our own ease. There is some reason to believe, too, that Mercury's day and year are the same length. This means that as the planet circles round the sun he turns once. If this is so the sun will shine on one half of the planet, producing an accumulated heat terrific to think of; while the other side is plunged in blackness. The side which faces the sun must be heated to a pitch inconceivable to us during the nearer half of the orbit-a pitch at which every substance must be at boiling-point, and which no life as we know it could possibly endure. Seen from our point of view, Mercury goes through all the phases of the moon, as he shines by the reflected light of the sun; but this point we shall consider mo

ny other heavenly body except the moon. Alas! when she is nearest, she like Mercury, turns he

well. She is at her best from our point of view when she seems to us to be furthest from the sun, for then we can study her best, and at these times she appears like a half or three-quarter moon, as we only see a part of the side from which the sunlight is reflected. She shine

T PHASES

we have to look away or wink hard at the sight; and the reflective power of the surface of Venus is as dazzling as if she were made of snow. This is probably because the light strikes on the upper surface of the clouds which surround her. In great contrast to this is the surface of Mercury, which reflects as dully as a mass of l

er than an earthly day, while others believe that the planet's day is equal to her year, just as in the case of Mercury. Venus's year is 225 days, or about seven and a half of our months, and if, indeed, her day and year are the same length, very peculiar effects would follow. For instance, terrible heat would be absorbed by the side of the planet facing the sun in the perpetual summer; and the cold which would be felt in the dreary winter's night would far exceed our bitterest Arctic climate. We cannot but fancy that any beings who might live on a planet of this kind must be di

there what it is here-that is to say, things will weigh at her surface about the same as they do here. Her orbit is nearly a circle, so th

facts have been learned by watching these transits. Mercury also has transits across the sun, but as she is so much smaller than Venus they are not of such great importance. It wa

THE EARTH, VEN

must see us like a little moon, with markings as the continents and seas rotate, and these will change as they are obscured by the clouds rolling over th

Venus does, and which, unlike her, is outside us in order from the sun, so that when it is nearest to us the full sunlight is on it. This is Mars, our neighbour on th

han the earth, his diameter is about twice that of the moon, and his density is about three-quarters that of the earth, so that altogether, with his smaller size and less density, anything weighing a hundred pounds here would only weig

sh Astronomical Asso

large

another disturbing fact turned up to upset their theories, and that was that they saw canals, or what they called canals, on Mars. These were long, straight, dark markings, such as you see on the map. It is true that some people never saw these markings at all, and disbelieved in their existence; but others saw them clearly, and watched them change-first go fainter and then darker again. And quite recently a photograph has been obtained which shows them plainly, so they must have an existence, and cannot be only in the eye of the observer, as the most sceptical people were wont to suggest. But further than this, one astronomer announced that some of these lines appeared to be double, yet when he looked at them again they had grown single. It was like a conjuring trick. Great excitement was aroused by this, for if the canals were altered so greatly it really did look as if there were intelligent beings on Mars capable of wo

later in the season parts near the pole turn brown. Thus the idea that the greenish parts are seas had to be quite given up, though it appeared so attractive. The idea now generally believed is that the greenish parts are vegetation-trees and bushes and so on, and that the red parts are deserts of reddish sand, which require irrigation-that is to say, watering-before anything can be grown on them. The apparent doubling of the canals may be due to the green vegetation springing up along the banks. This might form two broad lines, while the canal itself would not be seen, and when the vegetation dies down, we should see only the trench of the canal, which would possibly appear faint and single. Therefore the arrangements on Mars appear to be a rich and a barren season on each hemisphere, the growth being caused by the melting of the polar ice-cap, which sends floods down even beyond the Equator. If we could imagine the same thing on earth we should have to think of pieces of land lying drear and dry and dead in winter between straight canal-like ditches of vast size. A little water might remain in these ditches possibly, but not enough to water the surrounding land. The

e planet seems in every way fitted to support life, even if it is a little different from our earth. It is most certainly a living w

so infinitely small in regard to the space between them that there is no possibility of any one of them getting in such a position that it would throw a shadow on any other or eclipse it. The planets are like specks in space, and could not interfe

THE EART

is to say, every time we swing round our orbit we catch him up in a different plac

hese, the most favourable times of all, he is still more than thirty-five millions of miles away-that is to say, one hundred and forty times as far as the moon, yet comparatively we can see him very we

he planet in about ten hours. Now, as Mars takes more than twenty-four hours to rotate, this was considered ridiculous, for no moon known then took less time to go round its primary world than the primary world took to turn on its own axis. Our own moon, of course, takes thirty times as long-that is a month contains thirty days. Th

uch more than a brilliant star, and the inner one would be but a fifth part the apparent width of our own moon. So Mars is not very well off, after all. Still, there is gre

ommunication with Mars, and if it be inhabited by any intelligent beings, we may be able to signal to them; but it is almost impossible that any