A harvest moon looks big, doesn't it? Well, Jupiter from Ganymede is sixteen or seventeen times as wide as the Moon looks and it covers better than two hundred and fifty times as much sky. It hangs there in the sky, never rising, never setting, and you wonder what holds it up.
I saw it first in half-moon phase and I didn't see how it could be any more beautiful than it was. But the Sun crept across the sky and a day later Jupiter was a crescent and better than ever. At the middle of Sun phase we went into eclipse, of course, and Jupiter was a great red, glowing ring in the sky, brightest where the Sun had just passed behind it.
But the best of all is during dark phase.
Maybe I ought to explain how the phases work; I know I didn't understand it until I came to Ganymede. Ganymede is such a small planet and so close to its primary that it is tide-locked, just the way the Moon is; it keeps one face always toward Jupiter and therefore Jupiter does not move in the sky. The sun moves, the other Jovian moons move, the stars move—but not good old Jove; it just hangs there.
Ganymede takes just over an Earth week to revolve around Jupiter, so we have three and a half days of sunlight and then three and a half days of darkness. By Ganymede time the period of rotation is exactly one week; twenty-four Ganymede hours is one seventh of the period. This arrangement makes a Ganymede minute about a standard second longer than an Earth minute, but who cares? Except scientists, of course, and they have clocks that keep both sorts of time.
So here is the way a week goes on Ganymede: the Sun rises at Sunday midnight every week; when you get up Monday morning it's a little above the eastern horizon and Jupiter is in half-moon phase. The Sun keeps climbing higher and about suppertime on Tuesday it slides behind Jupiter and Ganymede is in eclipse; eclipse can last an hour or so up to a maximum of about three hours and a half. The stars come out and Jupiter shows that beautiful red ring effect because of its thick atmosphere. Then it's light again by bedtime Tuesday.
At noon on Thursday the Sun goes down and we start the dark phase; that's best of all. Jupiter's colors really show and the other moons are easier to see. They can be almost anywhere and in almost any combination.
Jupiter and its satellites is sort of a miniature solar system; from Ganymede you have a front seat for the show. There is always something new in the sky. Besides the eleven "historical" satellites ranging in size from Ganymede down to Jay-ten or Nicholson-Alpha, which is a ball of rock and ice only fifteen miles thick, there are maybe a dozen more a few miles or less in diameter but big enough to be called moons and heaven knows how many smaller than that. Sometimes these little ones come close enough to Ganymede to show discs; they mostly have very eccentric orbits. Any time there will be several that are conspicuous lights in the sky, like the planets are from Earth.
Io, and Europa, and Callisto are always discs. When Europa passes between Jupiter and Ganymede it is as big in the sky as the Moon is from Earth. It actually is as big as the Moon and at that time it is only about a quarter of a million miles away.
Then it swings around to the far side and is very much smaller—more than a million miles away and less than a quarter as wide. Io goes through the same sorts of changes, but it never gets as big.
When Io and Europa pass between Ganymede and Jupiter you can see them move with your naked eye, chasing their shadows or running ahead of them, depending on the phase. Io and Europa, being inside Ganymede's orbit, never get very far away from Jupiter, Io sticks within a couple of diameters of the big boy; Europa can get about sixty degrees away from it. Callisto is further out than Ganymede and goes all around the sky.
It's a show you never get tired of. Earth's sky is dull.
By six o'clock Saturday morning Jupiter would be in full phase and it was worthwhile to get up to see it. Not only was it the most gorgeous thing I had ever seen, but there was always the reverse eclipse, too, and you could see Ganymede's shadow, a little round black dot, crawling across old Jupiter's face. It gave you an idea of just how colossally big Jupiter was— there was the shadow of your whole planet on it and it wasn't anything more than a big freckle.
Jupiter is ninety thousand miles across the equator, eighty-four thousand from pole to pole. Ganymede is only a little better than three thousand.
For the next couple of days after full phase Jupiter would wane and at Sunday midnight it would be in half phase again, the Sun would rise and a new light phase would start. One thing I expected but didn't find was dim sunlight. Jupiter is a long way out; it gets only one twenty-seventh the sunlight that Earth does. I expected that we would always be in a sort of twilight.
It didn't work out that way. It seemed to me that the sunlight was just as bright as on Earth.
George says that this is an optical illusion and that it has to do with the way the human eye works, because the iris of the eye simply shuts out light it doesn't need. Bright desert sunlight back on Earth is maybe ten thousand foot-candles; the same thing on Ganymede is only four hundred foot-candles. But really good bright artificial light is only twenty-five foot candles and a "well-lighted" room is seldom that bright.
If you've got only a two-gallon bucket does it make any difference whether you fill it from the ocean or from a small pond? Sunlight on Ganymede was still more than the eye could accept, so it looked just as bright as sunlight on Earth.
I did notice, however, that it was almost impossible to get a sunburn.
11. "Share Croppers"
George got us a place to live when we had been there about a week, which was a lot better than most of the other immigrants did, but it didn't suit him and it didn't suit Molly and it didn't really suit me.
The trouble was he had to take a job as a staff engineer with the colonial government to get quarters for us—and that meant he would be too tied down to prove a piece of land for homestead. But it did carry private family quarters with it, if you could call two rooms twelve feet square a home.
It was like this: the colony was made up of homesteaders and townies. The townies worked for the government and lived in government-owned buildings —except for a very few who were in private trade. The townies included the Colonial Commission representative, Captain Hattie the pilot, the hydroponics engineers, the hospital staff, the engineers who ran the power plant and the heat trap, the staff of the local office of Project Jove, and everybody else who worked at anything but land farming. But most of the colonials were homesteaders and that's what George had meant us to be. Like most everybody, we had come out there on the promise of free land and a chance to raise our own food.
There was free land, all right, a whole planet of it. Putting up a house and proving a farm was another matter.
Here is the way it was supposed to work: A colonist comes out from Earth with his family and lands at Leda. The Colonial Commission gives him an apartment in town on arrival, helps him pick out a piece of land to improve and helps him get a house up on it. The Commission will feed him and his family for one Earth year—that is, two Ganymede years—while he gets a couple of acres under cultivation. Then he has ten G-years in which to pay back the Commission by processing at least twenty acres for the Commission— and he is allowed to process as much land for himself as for the Commission during the time he is paying what he owes. At the end of five Earth years he owns a tidy little farm, free and clear. After that, he can spread out and acquire more land, get into trade, anything he likes. He has his toehold and has paid off his debt.