Comets

In Our Time: Science

BBC

History

4.5 • 1.4K Ratings

🗓️ 17 January 2013

⏱️ 42 minutes

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Summary

Melvyn Bragg and his guests discuss comets, the 'dirty snowballs' of the Solar System. In the early 18th century the Astronomer Royal Sir Edmond Halley compiled a list of appearances of comets, bright objects like stars with long tails which are occasionally visible in the night sky. He concluded that many of these apparitions were in fact the same comet, which returns to our skies around every 75 years, and whose reappearance he correctly predicted. Halley's Comet is today the best known example of a comet, a body of ice and dust which orbits the Sun. Since they contain materials from the time when the Solar System was formed, comets are regarded by scientists as frozen time capsules, with the potential to reveal important information about the early history of our planet and others. With: Monica Grady Professor of Planetary and Space Sciences at the Open University Paul Murdin Senior Fellow at the Institute of Astronomy at the University of Cambridge Don Pollacco Professor of Astronomy at the University of Warwick Producer: Thomas Morris.

Transcript

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0:00.0	Thank you for downloading this episode of In Our Time, for more details about in our time, and for our terms of use, please go to BBC.co.uk.
0:09.0	I hope you enjoy the programme.
0:11.0	Hello, one evening in April 837 a strange new star was spotted in the skies above Northern Europe.
0:18.0	It was exceptionally bright and had a mysterious long tail.
0:22.0	Louis the Pius, King of the Franks, became convinced that it was a portent of his own death. He wasn't the only one to be worried. A scholar in Iraq recorded that this fiery apparition caused widespread terror, while in China the Emperor summoned
0:34.8	his astronomer royal to demand an explanation.
0:37.9	The object that caused so much concernation was Halley's comet, a small body of dust and ice
0:42.4	which orbits the sun and is visible from Earth
0:44.5	about every 75 years. Famously it appeared in 1066 just before the Roman invasion and it was most recently seen in 1986. Comets are some of the most spectacular objects in the night sky,
0:56.4	but are rarely visible to the naked eye, although two unusually bright comets are forecast for later this year.
1:01.9	So where do comments come from? What do they consist of? are us comets are Monica Grady, Professor of Planetary and Space Sciences at the Open University.
1:16.4	Paul Murden, Senior Fellow at the Institute of Astronomy at the University of Cambridge,
1:20.9	and Don Polacko, Professor of Astronomy at the University of Warwick.
1:24.5	Paul Nurden, can you tell us about comets?
1:28.1	There's been attempts to describe them for over 2,000 years, but can you tell us exactly
1:32.4	what a com comet is?
1:34.0	Well, comets are akin to planets, as you said, in that they orbit around the sun through the
1:38.6	solar system. They're solid bodies, they're typically lumps of ice, maybe in the range a few meters in diameter up to perhaps 100 kilometers in diameter.
1:50.0	And they have orbits which are distinctly non-planetary.
1:56.6	The planets all march in an orderly fashion around the sun, all going around in the same
2:00.4	direction, going in orbits that are more or less circular, and going in orbits
2:05.6	which are all in the same plane. But comets come from every direction in the sky and their
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