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.