杏吧原创

is a sight to see. When this moving speed bump of water races round a bend in the UK鈥檚 longest river, spouting spray up onto the bank and startling the swans, you can鈥檛 quite believe your eyes. It is hard to believe that the moon, a quarter of a million miles away, reaches out with its gravitational fingers to fashion such a localised thing. But the Severn bore is striking evidence, if evidence is needed, that the Earth is not, in the words of the late Carl Sagan, an isolated 鈥減ale blue dot鈥�, but prey to celestial influences from near and far.

Lunar tides, though regular, are idiosyncratic enough to baffle. Perhaps that is why it took the genius of Newton to realise they were caused by the gravitational pull of the moon, which varies in strength across the globe.

The tides are just the beginning. In Heaven鈥檚 Touch, astronomer describes in detail how the moon, sun and planets continually nudge the Earth鈥檚 spin axis and orbital plane, triggering mundane effects, such as the wandering of the north celestial pole, and more catastrophic effects like ice ages. It is this kind of technical detail that differentiates Heaven鈥檚 Touch from last year鈥檚 book by Jeff Kanipe, The Cosmic Connection.

The real surprise of the past few decades must be the vulnerability of the Earth to truly cosmic events 鈥� not only supernovae, whose 鈥渒illing zones鈥� may extend within 30 light years of us, but also gamma ray bursters whose emissions, beamed like death rays, could scour life from planets 6000 light years away. I have a soft spot for magnetars, ultra-dense neutron stars with the strongest magnetic fields in the universe, and Kaler covers these in detail. In 1998, the eruption of one such star 20,000 light years away generated X-rays so powerful that anyone in Earth orbit would have had the equivalent of a dental X-ray. Six years later, the Earth was irradiated by a magnetar outburst 100 times more powerful.

All these phenomena and more are described authoritatively by Kaler who predictably, but fittingly, ends with our most intimate connection to the cosmos. The iron in our blood, the calcium in our bones, the oxygen that fills our lungs each time we take a breath 鈥� all were forged in the furnaces of stars that lived and died before the Earth was born. We are stardust made flesh. Or, as the American astronomer put it: 鈥淲e are all brothers 鈥� we were all born in the same supernova explosion.鈥�