Christmas comes but once a year and some planetary scientists might say that's quite enough. I think we could do with more.

Not like the one five years ago, however, when Beagle 2 had the nation in tears as we searched for a radio signal from Britain's Mars lander. It steadfastly refused to respond to all our calls; I seem to remember thinking of the carol Silent Night, first performed on Christmas Eve, 1818. Legions of the fans we inspired were disappointed when they asked "What happened to Beagle 2?" instead of "Where are my presents?"

While the country listened to the Queen's Speech (we were told it would have mentioned us had we succeeded) the Jodrell Bank telescope vainly scanned the skies in case it detected a distant bark. It was a double whammy of a disappointment, because the previous Christmas and New Year had been sacrificed to putting the spacecraft together.

Not all my Christmases have been quite so depressing. I remember the excitement when, 40 years ago, Apollo 8 took astronauts Frank Borman, James Lovell and William Anders behind the Moon. Christmas evening 1968 is memorable for their reading from the Book of Genesis, and the "awe-inspiring" vision of Earthrise during a live television broadcast.

ÖйúAƬ

That particular crew undertook what I think was the second most dangerous mission of lunar exploration. Flight controllers, and those of us working on the Apollo programme, certainly were relieved when they emerged, especially me. Analysing returned lunar samples was my first job as a postdoc.

Apollo 8 was the dawn of a new era. It was my reality check. JFK's promise that the US would "choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard" was going to be fulfilled and I didn't need any more inspiration.

ÖйúAƬ

A few weeks later, I was in the audience when Borman visited the UK and spoke at the Royal Society. The room was packed. It's often said that astronauts inspire the young, and Britain's scientific elite were inspired that day; there were venerable gentlemen jostling for a better view of a rather diminutive figure. I stood at the back; at least I saw the top of his head.

The intrepid explorer had an audience with the Queen as I walked back towards Piccadilly. I thought how brilliant it would be if I could always attend such events. I got my wish 25 years later when I was elected a fellow. It wasn't that I came away inspired in 1969 but I was motivated by the occasion, even if it meant working the next Christmas Day so I could reveal the secrets of the Moon to the world. All the investigators had to agree to an embargo on announcements until 3 January 1970.

Back to the Royal Society. Edmond Halley, who became a fellow, would have had a happy Christmas if he had been alive on 25 December 1758. On that day, Polish astronomer Georg Palitsch spotted the comet whose reappearance, no one will forget, was predicted by an Englishman. Halley asked only that he be remembered for getting it right. Having his name associated with one of nature's most spectacular occurrences started the trend of referring to comets by the name of their discoverer. I recently gave the "Halley lecture" to 200 boys at the scientist's old school, St Paul's; I hope I inspired a few of them.

Of course Halley would have got nowhere but for Isaac Newton who was born on 4 January 1643, or 25 December according to the Julian (old style) calendar. He provided the maths Halley needed. My grandfather was born (and died) on Christmas Day using the modern Gregorian version of the calendar.

William the Conqueror was crowned on Christmas Day, 1066, in Westminster Abbey, where can be found the remains of Charles Darwin, who left us the legacy of the theory of evolution. The latter set sail in December 1831, to go round the world on HMS Beagle. The objective of Beagle 2 was to discover whether life had evolved on another planet; it gave my wife the idea to coin the project's iconic name in honour of the naval vessel.

William had a connection to Halley, since the 1066 apparition of the comet is depicted on the Bayeux Tapestry, the record of the Norman Conquest. Another apparition of Halley's Comet occurred in 1305. It was painted by Giotto in the nativity scene on the wall of the Arena Chapel in Padua. Giotto's fresco was the inspiration for the European Space Agency to call its Halley fly-by mission after the artist. My group at The Open University has a mass spectrometer on another inspirational spacecraft called Rosetta that will rendezvous with a comet, land and fly with it into the solar system in six years from now.

The nativity scene wasn't a part of Christmas until St Francis of Assisi invented it for Christmas, 1223. The day wasn't even celebrated until the 4th century, so the debate about the year of Christ's birth is an anachronism. It was St Matthew who introduced the idea of the Magi, astrologers, not astronomers, who followed the star in the east.

There have been bitter arguments over the nature of the "Star of Bethlehem". Some favour a comet; others think it might have been a supernova. Historical records do not mention acceptable examples of either.

ÖйúAƬ

ÖйúAƬ

A more well-received explanation involves planetary conjunctions: when two or more planets are so close together in the sky that they enhance each other's brightness. There were suitable occurrences in the required time-frame: one of Jupiter and Venus just above the horizon in 2BC, and a very bright instance involving the gas giants Jupiter and Saturn, in 7BC. If the latter is correct, then Christmas Day should be on 15 September. A Mars-Jupiter conjunction was reported in The Times ÖйúAƬ Supplement (as it was then known) at Christmas 1986.

Another Christmas planetary gem is the fact that Galileo didn't discover Neptune. He saw it on 28 December 1612, but he thought it was a star. Neptune had a bit of a charmed life when it came to attempts to discover it. A young British astronomer, John Couch Adams, was bold enough to predict its existence in his 1845 thesis. The Astronomer Royal of the time, George Biddell Airy, was unimpressed, so a Frenchman completed the job.

Biddell Airy's claim to fame was that he secured the Meridian line for Greenwich; the ungrateful French said they would agree to it only if Britain adopted the metric system.

For those expecting to play Trivial Pursuit this Christmas, here are a few more space anniversaries. On Christmas morning 2004, the European Space Agency's Huygens lander separated from its mother craft, Cassini, to land on Saturn's moon Titan in January, 2005. Christmas Eve 1979 saw the launch of the Ariane 1 rocket. The Russians don't have their official holiday until 7 January, so they put their space station Salyut 4 into orbit on Boxing Day 1974 and landed Venera 11 on Venus on 25 December 1978. Venera 5, the first-ever successful planetary landing, took place on Twelfth Night, 5 January 1969; Nasa chose the same date in 1972 to announce that it was going to build the Space Shuttle.

The Quadrantid meteor stream can also be seen on Twelfth Night, which brings me nicely to my favourite subject: meteorites. They can serendipitously land at any time to enhance our knowledge of the solar system. The biggest fall of meteoritic material in Britain arrived as a shower on Christmas Eve 1965. Naturally, those interested in the subject spent the festive season ransacking Leicestershire in the hope of finding a piece to do some inspired research.

The first meteorite accepted as a stone from the sky fell to Earth on 13 December 1795 at Wold Cottage in Yorkshire. Major Edward Topham, owner of the property and an early newspaper proprietor, led a campaign to get the 56lb (25kg) stone accepted as extraterrestrial. His ten-year-old daughter Harriet was inspired to produce an enchanting illustration complete with dimensions for the philosophers, as scientists were then called.

I believe the colourful Topham was instrumental in the subject of meteoritics becoming fashionable. He was renowned for his bushy sideburns - no, he didn't inspire me to grow mine, but he did teach me about the power of the media when it comes to delivering inspirational messages.

There are a few meteorites that come from the Moon and Mars. The realisation that the latter might carry evidence of life on the Red Planet drove me to launch Beagle 2 in an effort to prove it.

The vast majority of meteorites come to us from the asteroid belt. We found out about asteroids only when Giuseppe Piazzi recognised the first, and largest, Ceres, on New Year's Day 1801. When the King of Italy offered Piazzi a gold medal as a reward, he replied that he'd rather have a better telescope.

You see, planetary explorers are not just prepared to work over Christmas but we do it for little reward other than a name check. Piazzi didn't get his, but since 2005, Asteroid 15614 has been known as Pillinger. If anyone feels inspired to have an asteroid named after them, they should become a planetary scientist. l

ÖйúAƬ