The Moon

Reflected Moon on Paddy-fields in Sarashina

by Hiroshige Utagawa

The full moon of August will be with us tomorrow. In one ceremony of ancient Japan this moon, seen reflected in water, symbolized more than anything else the mystery and transience of life. But to see the Moon at any time, and at any phase, can be an awe-inspiring experience. Whether you are in the comfortable north-western suburbs of London or camped out on an Antarctic ice-floe, the Moon presents the same inscrutable visage.

It is a true wilderness, remote, aloof from our concerns, and, except for the assorted junk left behind by space programmes, as yet unbefouled.

The familiar pattern on the Moon (representing a man’s face, a hare, a beetle, the Madonna and Child, or a dozen others, depending on your culture) is made up of the darkness of plains contrasted with the brightness of mountains. Seen with binoculars, the pattern disappears at once, and it is only then, with the Moon filling your field of view, that you get some idea of its majesty and size.

For, although the Moon is held to be a mere satellite of the Earth, it is much bigger than the moons of Mars or Jupiter, being over 1/5th the weight of the planet Mercury. Indeed, according to one theory of the Moon’s origin, it was once a small planet, with an independent orbit.

This theory suggests that, at some time at least four billion years ago, the Moon passed sufficiently close to the Earth to be “captured” by the Earth’s gravitational field. As the Moon passed there would have been huge tides, miles high, in the Earth’s oceans. The energy to produce these tides was thus transferred from the Moon to the Earth, slowing the Moon down and preventing it from getting away.

There is a theoretical limit at which any satellite can remain intact, called the Roche limit, which, in the case of Earth, is about 3,700 miles from the planet surface. Once the Moon reached the Roche limit it began to break up, losing half its mass to the Earth, especially the heavier rocks containing iron. This material became the present continental land masses.

The remnants, now just outside the Roche limit, gradually reformed into a sphere and began to retreat, towards the Moon’s present mean distance of almost 240,000 miles from the Earth.

An older theory was that the Moon was originally torn from the substance of the Earth, leaving behind the scar which we now call the Pacific Ocean. Recent understanding of the way continents drift makes this idea seem less likely, as does the fact that rock samples brought back by the Apollo missions prove that the geology of the Moon is very different from that of the Earth.

All the planets in our solar system, and their satellites, were formed by clouds of gas from the Sun, but not all were formed at the same time or from the same cloud. Another theory of the Moon’s origin is that the Moon has always been in the Earth’s orbit, but was formed from a different cloud. Of the three theories, the first is perhaps the most favoured today. Since we do not yet even know in detail how the Earth was made, it may be premature to expect firmer knowledge just yet.

These are matters for the physicists and mathematicians to ponder. But it requires no special knowledge to look at the Moon, and if you have even an old pair of opera glasses you can follow in the tradition set by Galileo, who first turned a telescope on the Moon in 1610. Although he probably knew that no large expanses of water were to be found there, it was he who named the dark areas maria (seas) and the light ones terra (land).

These terms have survived to the present day, inappropriate as they are. We now know that the Moon’s surface is almost unbelievably harsh. When Neil Armstrong took that “giant step for mankind” on 21 July 1969, he stepped into a desert of black, basaltic dust and rock, baked during full sunlight to the temperature of boiling water and frozen during the lunar night to the temperature of liquid air.

On the Moon there are mountains higher than the Himalayas and craters up to 180 miles across and 2,600 feet deep. The atmosphere is extremely thin, for the Moon’s gravity is only 1/6th that of Earth. This means that there is almost nothing to protect the Moon from the impact of meteorites, the chunks of rock which, hurled out perhaps thousands of years before by some disintegrating star, travel on and on through empty space until they meet an obstruction. Most of those striking the Earth get burned up by friction with our thick atmosphere: not so on the Moon.

The surface of the Moon is buried to a depth of several feet in meteorite debris. Its entire surface is pockmarked with craters, from the microscopic to the gigantic. When the impact is especially great, splashes of moondust are thrown in all directions. These bright splashes are called “rays”, and, until disturbed by further impacts, may clearly be seen from Earth.

One of the most perfect craters, as yet virtually undamaged by subsequent impacts, is Tycho. This is in the southern hemisphere, at about the same latitude as New Zealand is on Earth. The 54-mile wide crater has a sharp central peak and walls which rise to 16,000 feet.

The splashes radiating from Tycho have spread out across almost the entire visible face of the Moon, one ray even being seen to cross the Sea of Serenity in the northern hemisphere. The best views of the Moon are usually to be had at other phases, when the slanting sunlight makes the surface stand out in sharp relief, but full moon is the time to see the rays of Tycho.

The full moon – and what better than the August one, traditionally the moon to be viewed – is also, perhaps, the most impressive and the most suitable way of reminding ourselves of the true value and scale of things.

(Introduction to these pieces; see all)

Flaunden by Night

As the winter deepens the cold is becoming more intense. By midnight the puddles on the bridle path are frozen almost solid and no longer break so easily underfoot. There has not yet been snow, but soon, perhaps, when the wind changes and cloud covers the sky, it will begin.

Meanwhile, nightly frosts are preparing the ground for it. Each morning the patterns on the windowpane take longer to disperse, and last night, the coldest yet, there was a loud report from the garden, like a pistol shot. The temperature had fallen so much that the sap in a high cedar bough had frozen, expanded, and split the wood.

The moon was out then too, the frost’s accomplice, high and small and glaring white. The bluish-silver light is casts on the bridle path is treacherous and not to be relied upon, but still you do not take the torch from your pocket, for your eyes are only now becoming adapted to the dark.

There is a childish excitement about an excursion like this, when sensible people are already warm in bed. You would be in bed now yourself, had you not suddenly decided to come out and see the sky.

Winter is a good time for stargazing. The nights are deep and the north wind drives impurities and heat haze away. The other bane of the amateur astronomer is the orange glow of sodium streetlamps, which extends for a surprising distance into the atmosphere. Out here, however, some distance from the nearest town, the sky is black to the horizon.

Emerging from the shelter of the hawthorns, the bridle path runs beside a barbed wire fence and there, downhill across invisible fields, the whole of the southern sky opens out to view.

The patterns of stars, the constellations we speak of, bear little resemblance to the objects, creatures, or personages they are supposed to represent. In different ages and through different eyes the stars must have been arranged in many other ways, fitted to the legends and heroes of the time.

A few constellations, though, must always have been recognized in the shapes we know today. Cassiopeia is one, tonight an M rather than a W, hanging slantwise at a neck-stretching angle in the top of the sky.

Another is the giant figure which, eternally wheeling westwards, comes in winter to dominate the southern sky. Orion was surely always a hunter, a warrior. In our almagest he is locked in endless combat with Taurus, the bull. At his feet is Lepus, the hare. Orion’s shoulders are made by Bellatrix and the red star Betelgeuse, and his rightmost ankle is the brilliant Rigel. His belt-buckle has Alnilam for a jewel; below hangs his sword, in which is visible, even to the unaided eye, the luminous cloud of the Great Nebula.

Nearby, his two hounds are in attendance. The three stars of his belt point down to the larger, Canis Major, in which is the blazing blue-green cauldron of Sirius, the dog star, the brightest in the sky.

Sirius is so dazzling that it is difficult to see the lesser stars which immediately surround it. In the last century the astronomer Bessel noticed that Sirius seemed to be moving in a small orbit, and thought there must be a dark companion star. His idea was confirmed in 1862. Although the companion star is so much dimmer than Sirius, its surface temperature has been found to be about the same, and so, incredibly, the difference in brightness much be due to a difference in size.

The companion, Sirius B, is a white dwarf, in diameter an object only about three times the size of Earth. It contains as many atoms as our sun, but the spaces inside each atom have collapsed. Sirius B now has a density some fifty thousand times that of water, and just one teaspoon of it would weigh almost a ton.

The vast emptiness of Orion’s limbs is almost like the emptiness of our own when compared with the stuff of Sirius B. Like the puddles in the bridle-path, like the cedar tree, like everything else on earth, we are made not so much of solid stuff as of vacancy.

Walking back, having spent a long time standing in the darkness and marvelling, you somehow feel no longer quite so insignificant or remote. The torch-beam is playing on the iron-hard ruts and ice; the basic laws of physics down here are just the same as those up there.

The wind is moving in the hawthorn branches. It has changed direction. Before dawn there will probably be cloud, low, dense, and tinged with yellow, and not long after that it will probably start to snow.

(Introduction to these pieces; see all)