Stars and planets: August

Our search for an alien intelligence (SETI) in the universe has just taken a giant leap forward – but the chances of detecting that first significant call from ET may be scuppered by giant volcanic eruptions on his home planet. Those were the messages of optimism and pessimism to emerge from this month's international conference on bioastronomy, held on Hamilton Island on Australia's Great Barrier Reef.

First, the good news. The SETI Institute, based in California's Silicon Valley, has begun building the most powerful radio telescope yet constructed to search for alien radio messages. The search for extraterrestrial intelligence began in 1960, and so far there have been about 100 different attempts to pick out an intentional signal from aliens to the Earth. But these have all been limited. Some have used small and outdated radio telescopes, retired from active astronomy research. Others have "piggybacked" on larger radio telescopes doing different kinds of astronomy. Instead of having the freedom to check out likely stars with life-bearing planets, the latter are forced to search wherever the telescope happens to be looking.

The prime purpose of the telescope the SETI Institute is building is to seek out ET. It's thanks to an $11.5m (£8.2m) donation from Paul Allen, who co-founded Microsoft with Bill Gates, and a further $1m from Nathan Myhrvold, a former chief technology officer at Microsoft.

The Allen Telescope Array is revolutionary. It's not a single radio telescope, but an array of 350 individual dishes, each 6m (20ft) across. To make the instrument affordable, these are off-the-shelf satellite TV dishes. Linking them together will create a radio telescope more powerful than Jodrell Bank.

Two weeks ago, the first of these telescopes was set up at Hat Creek, 300 miles north-east of San Francisco. The big array should be complete in 2005. To help meet costs, the SETI Institute is offering to name each dish in return for a $50,000 donation.

Apart from the random piggyback searches, SETI researchers have been limited to investigating just 1,000 nearby stars that are like the Sun, hoping they'll have Earth-like planets where aliens are busy sending radio waves into space. The Allen telescope will be able to eavesdrop on almost a million different stars.

That makes a big difference. Even the most optimistic SETI enthusiasts think we'd be pretty lucky if one in a thousand stars hosted an advanced alien civilisation. But many scientists think it's odds on that at least one civilisation will evolve in a sample of a million stars. And, as the Sun is a relatively new kid on the cosmic block, this civilisation is probably millions of years ahead of us. But we'll only detect their radio signals if the civilisation can last for millions of years. And Mike Rampino, of New York University, thinks that's unlikely.

Rampino, a volcano expert, told the bioastronomy conference that the volcanoes we see on Earth today are pretty tame. Even an explosion like the one at Krakatoa only hints at the "super-eruptions" our planet can produce. About 73,000 years ago, the Sumatran volcano Toba blew apart in an explosion a thousand times greater than Krakatoa. It blasted 10 billion tonnes of ash high into the stratosphere, blocking sunlight from the Earth's surface, where temperatures would have plummeted at least five degrees over the whole globe. Local effects could have been worse, leading, Rampino suggests, to snowfalls in the Sahara.

This global cooling would have been lethal for vulnerable life-forms, such as early humans. And genetic studies suggest that the population did crash at about this time, from 100,000 humans to a few thousand. Despite our technologies, humans today would be equally vulnerable. Rampino is convinced that our civilisation would totally collapse.

In fact, Rampino estimates that super-eruptions are twice as likely to wipe out our civilisation as an impact from an asteroid – with a frequency of about once every 50,000 years. On that reckoning, we are about due for another super-eruption at any time. And where will it happen? Ironically, the planet's most technologically advanced nation also harbours one of the Earth's most lethal volcanic hot-spots – the Yellowstone National Park region of Wyoming.

WHAT'S UP

It's a month for celestial fireworks: a shower of meteors is set to liven up the middle of the month. Though it looks like a falling star, a meteor is in fact a small speck of dust in space that burns up in the Earth's atmosphere. During August, our planet runs into a trail of dust shed by a comet called Swift-Tuttle, and so we experience a shower of shooting stars.

These meteors all seem to spread out from the same point in the sky, in the constellation Perseus – hence their name, the Perseid meteor shower. You'll spot some Perseid meteors throughout the first three weeks of August, but they build to a maximum on the night of 12-13 August. The best time to watch is after midnight, when the crescent Moon has set and the Earth's spin is taking us into the interstellar debris at maximum speed.

The Perseids are the "old faithfuls" of the meteor world: it's relatively safe to predict how many you'll see – unlike the temperamental November meteor shower, the Leonids, which has come up with storms of meteors over the past couple of years.

In fact, the Perseids have been getting more sparse over the past few years, as comet Swift-Tuttle is gradually heading away from the Earth and back to the outer parts of the solar system. The International Meteor Organisation predicts that this year you'll see about a meteor a minute.

On the planetary front, Venus is sinking into the evening twilight, but still prominent as it grows gradually brighter. At the end of the month, it passes close to Spica, the principal star in the constellation Virgo (the virgin). Saturn is now rising in the northeast around midnight, and Jupiter in the early hours.