Measuring the sky

This civilization lived by the water. On the shore of Lake Edward, some twenty thousand years ago, people fished, gathered, and made harpoons of bone. One of them took a thin piece of bone, set a chip of quartz at its end, and began to cut.

The cuts are small and deliberate. They run in three columns along the shaft, gathered in groups, as if the hand had paused between each set and started again. Someone was keeping something: a count, a sequence, a record of days. We do not know which. The order of the groups looks intended, and that is almost all that can be said with certainty.

In the first century BCE, a cargo ship went down off the small island of Antikythera, between Kythira and Crete. It carried statues of bronze and marble, glassware, coins, and a wooden case not much larger than a stack of books. Two thousand years under the sea turned the case into lumps of green stone. In 1902, a year after they were brought up, someone looking closely saw a toothed wheel.

This civilization had built a machine to hold the sky. Turn a handle, and pointers moved across its dials: the Moon with its phases and its uneven pace, the Sun through the signs of the zodiac, the calendar of the games, the months in which an eclipse would come. Its teeth were cut by hand in thin bronze, its instructions engraved in tiny Greek letters on its plates.

This civilization wrote at the edge of a desert. Timbuktu stood where the caravans from the Sahara met the boats of the Niger, and with salt, gold and cloth came paper and books. Families copied them, bought them, annotated their margins, and passed them down.

The pages speak of everything. How to read the stars to know the seasons. How to divide an inheritance. How to treat a fever with plants and minerals. How to add and multiply. How the soul draws nearer to God. Some are in Arabic, others in African languages written in Arabic letters. Kept in chests and in family rooms, they survived heat, dust and termites for centuries.

This civilization lived on atolls so low that a coconut palm showed above the horizon only some twenty kilometres out to sea. Its navigators did not look for land; they felt for it. A swell rolling in from the east bent around an island, struck its reef and sent back a fainter wave, and a canoe crossing these meetings of water rocked in a way the body learned to recognise.

What is kept here is how that recognition was taught. Thin sticks lashed with fibre: the straight ones for currents and regular waves, the curved ones for the great ocean swells, and small shells tied on for the atolls. It was never taken to sea. A learner studied it ashore, committed it to memory, then left it behind. The chart travelled inside the navigator.

If you are holding this, you found it very far from us. It left in 1977, fixed to the side of two spacecraft, Voyager 2 in August and Voyager 1 in September, and it was addressed to no one this civilization knew.

It is a record: a disc of copper plated with gold, a foot across, packed with a cartridge and a needle. The cover is our instruction for use, cut in lines rather than words: how to lower the stylus, how fast to turn the disc, how to rebuild the pictures stored in the grooves, and where our Sun lay, measured against distant pulsars. A trace of uranium was plated onto it so that you could tell how long it had travelled.