The stars: The Moon obscured

The September sky, by Heather Couper and Nigel Henbest

If the Moon looks a bit odd on 16 September, don't be too worried. As it rises, around 1900 BST, the Moon will be largely in Earth's shadow. A few minutes later it will be entirely obscured. This total eclipse ends at 2018, when you will see the Moon begin to emerge again above the eastern horizon.

Two weeks earlier, people in Australia and New Zealand will be treated to the sight of the Moon blocking off part of the Sun's brilliant disc. The eclipse will not be total anywhere in the world, but if you are in the southern parts of those two countries you will see more than half the Sun obscured on the morning of 2 September.

Back in the night sky, brilliant Jupiter is still lording it over the heavens. The Moon is near it on September 13, and passes the next planet, Saturn, on 18 September.

Saturn is the most distant planet we can see with the naked eye, but in space terms it's only on our back doorstep: sunlight reflected from it takes about an hour to reach us. High above Saturn and Jupiter are three bright stars forming the Summer Triangle. The star at the lower point is Altair: its light takes 16 years to reach us. Deneb, to its upper left, is 1,800 light years away. But the Andromeda Galaxy, visible as a faint blur to the east, is 2 million light years from us: we see it as it was when our ancestors in Africa began to look human.

When we look to more distant galaxies, telescopes become time machines, revealing the cosmos as it was far in the past. Last month, the Hubble Space Telescope found the most distant object yet detected: an anonymous galaxy about 12 billion light years away. That light we see now left it long before the Sun and Earth were born.

We are currently living some 13 billion years after the Big Bang, in which the whole universe began. So we see this infant galaxy as it was only 1 billion years after the Big Bang. And the Hubble pictures show it as a hotbed of action, ablaze with the birth pangs of the first generation of stars.

But we can probe still more deeply into space and time. Radio telescopes pick out a "glow" from even farther afield, almost 13 billion light years off. This is radiation from the Big Bang itself. Observations like these have shown that the Big Bang is not just a theory, to be set alongside conjectures like the Fifties Steady State hypothesis (which said the universe was infinitely old).

In 1992 the orbiting Cosmic Background Explorer (Cobe) found "ripples" in this background radiation, now confirmed with sensitive radio telescopes set up by British astronomers in the Canary Islands. The ripples show where the gases from the Big Bang began to curdle into denser clumps, which became galaxies.

European astronomers are now planning a follow-up to Cobe, called Planck, which will explore these ripples in much more detail, and answer the last great remaining question in cosmology: how do the clumps of gas from the Big Bang turn into infant galaxies like that just discovered by Hubble? So the answers we are seeking will provide the clue to our own ultimate originn

All the latest information on the origin of the universe is to be found in the authors' book `Big Bang' (Dorling Kindersley, pounds 9.99).

September diary (24-hour, BST)

1-2 2244-0323: partial eclipse of Sun (Australia and New Zealand)

2 0052 new Moon

10 0231 Moon at first quarter

16 1916-2018 total eclipse of Moon; 1951 full Moon;

Mercury at greatest western elongation

22 2356 autumn equinox

23 1436 Moon at last quarter