Comets are lumps of rock left over from the formation of the Solar System. Fleetingly they appear in our skies, and just occasionally they can be celestial divas. Here are some of the most spectacular comets, recorded from the time when superstitious people considered them harbingers of doom, up to the present day.

Caesar

The week-long visitation of a brilliant comet following the assassination of Roman dictator Julius Caesar in March 44 BC confirmed his divine status to the people of Rome. The Emperor Augustus even had coins minted in Caesar's honour which displayed the comet on the reverse side. Chinese astronomers, who thought comets were 'celestial ambassadors', recorded this fleeting visitor a full month before the Romans saw it, but no doubt they called it something other than Caesar's Comet. As it was seen from their nation's capital, 'Comet Chang'an' could have had a nice ring to it.

Charles V

The Great Comet of 1556 was named after Charles V, the Holy Roman Emperor. This VIP was also king of Germany, Italy and Spain, and Lord of the Netherlands as well. When he saw the comet Charles V thought it a sign for him from Heaven so he sent for a philosopher called Eginard to discuss what it could mean. The upshot was that Charles V retired to a monastery. Fast forward to the 19th Century and English astronomer John Russell Hind¹, after studying the report of Friar Giles of Cambridge on the Great Comet of 1264, declared that it and Comet Charles V were the same comet on a return visit. If this was accurate then a further return could be expected around 1848. Unfortunately it didn't materialise, so we can only speculate on a possible return of the comet in 2140 to prove Hind correct.

• The Great Comet of 1264 saw out a pope, Urban IV. There is a legend that involves him and Tannhäuser, a German poet. According to the story, Tannhäuser found the Venusberg, spiritual home of the Roman goddess Venus, and during his time there he became so entranced that he put aside his Catholic convictions and worshipped Venus instead. After a crisis of conscience, Tannhäuser journeyed to seek the absolution of the Pope, but was refused. Heartbroken, he returned to Venusberg. This story inspired the opera Tannhäuser by Richard Wagner, which he began writing and composing the music for in the 1840s, uncannily around the time of the comet's anticipated return.

De Chéseaux

The Great Comet of 1744 was named after the Swiss astronomer Jean-Philippe Loys de Chéseaux (1718 – 1751) even though he was not the first person to learn of its existence². Comet de Chéseaux was visible to both hemispheres of Earth and it must have been a spectacular sight indeed, with its six tails spread across the sky like a cosmic fan.

• One awestruck viewer of Comet de Chéseaux was French teenager Charles Messier, who was inspired to become an astronomer and comet hunter through this encounter.

Donati

Italian astronomer Giovanni Battista Donati (1826 - 1873) discovered Comet Donati in 1858. It has the distinction of being the first comet ever to be photographed, at Harvard College Observatory in Cambridge, Massachusetts, USA.

• Down on Earth, the first transatlantic telegraph message was sent and received. Emmeline Goulden was born in Manchester, England; she would later become Emmeline Pankhurst, leader of the British suffragette movement. Time magazine listed her as one of the 100 Most Important People of the 20th Century.

Flaugergues

The Great Comet of 1811 was discovered by French astronomer and archaeologist Honoré Flaugergues (1755 - 1835). It was, by all accounts, a visual treat for non-astronomers as well as an unforgettable experience for comet enthusiasts. Of all the comets known at that time, it was the one that was visible for longest, a record it held until Comet Hale-Bopp overtook it at the end of the 20th Century. Comet Flaugergues is sometimes referred to as Napoleon's Comet, as the French Emperor was making plans to invade Russia at the time, but that didn't turn out so well for him.

• In 1811 the first steam-powered ferry service commenced between New York City and Hoboken in New Jersey. The German inventor and chemist Robert Wilhelm Bunsen was born, as were conjoined twin brothers Chang and Eng.

Hale-Bopp

Comet Hale-Bopp was discovered in July 1995 by two independent observers, professional astronomer Alan Hale, and amateur astronomer Thomas Bopp using a borrowed telescope. As was the normal practice of the time, Bopp sent a telegram to the Central Bureau for Astronomical Telegrams, announcing his discovery. Hale, on the other hand, had access to a new contraption known only to a few people: the Internet. He had already e-mailed in his discovery and two updates on the new position of the comet before Bopp's telegram arrived. The Internet was responsible for spreading the news instantaneously worldwide and Hale-Bopp featured on the new Astronomy Picture of the Day website many times. The twin-tailed apparition was visible to the naked eye for just about 17 months, from May 1996 until September 1997, which makes it the current endurance champion and probably the most widely-observed comet in history.

• Along with Comet Hale-Bopp's popularity with the astronomy profession and the general public alike, some notoriety came in the form of the Heaven's Gate UFO religion group. Their leader predicted that an alien spacecraft, hidden behind comet Hale-Bopp, would take their souls to another planet if they all committed suicide. As a result 39 people, including the leader, killed themselves in March 1997. The question of whether they attained their desired goal or not remains unanswered.

Halley

Halley's Comet is the most well-known comet of all; it holds the distinction of being the first recognised periodic comet, returning approximately every 76 years. English astronomer Edmond Halley (1656 - 1742) worked out its orbit in 1682. He correctly predicted the comet's next return to the inner Solar System, so it was posthumously named in his honour. Halley was a contemporary of Sir Isaac Newton; in fact he prompted Newton to rewrite his lost notes on gravity and publish them.

• Modern day astronomers have traced Halley's Comet back to 240 BC by comparing historical records kept by ancient civilisations like the Babylonians and the Chinese. An earlier possible sighting is being investigated, as there was a comet visible for about 75 days during 466 BC. The comet was seen in Greece; mention of it was later recorded by Pliny the Elder, who documented a brown meteorite the size of a wagon load³ which fell to Earth while the comet was visible in the sky. Did the ancient Greeks think that a piece of the comet had sheared off? It's an intriguing thought, but nevertheless it was probably just a coincidence.

Holmes

Comet Holmes has been visiting the inner Solar System approximately every seven years since 1892. Up to 2007 it was nothing to get excited about. That soon changed when Comet Holmes underwent an eruption, brightening it to 3rd magnitude over a period of 42 hours. The comet's coma expanded to 1.4 million km (869,900 miles) in diameter, making it, for a while, bigger than the Sun. Comet Holmes returns to the inner Solar System in March 2014. Will it put on another stunning performance, or will it be a damp squib? Only time will tell.

• Comet Holmes was discovered by English amateur astronomer Edwin Holmes in November 1892. At that time Sir Arthur Conan Doyle published a collection of 12 short stories about a detective who was about to become a global phenomenon: The Adventures of Sherlock Holmes. One of the craters near the Apollo 17 landing site on the Moon was called Sherlock by geologist/astronaut Harrison Hagan 'Jack' Schmitt, who was a student of Dr Eugene Shoemaker.

Kirch

The Great Comet of 1680 was the first one discovered by telescope, by German astronomer Gottfried Kirch. Sir Isaac Newton studied this comet's behaviour and realised that when it disappeared and later reappeared in a different part of the sky, it had in fact gone around the Sun and was now heading away from it. Newton included a diagram of its orbit in his Principia⁴ of 1687.

• Comet Kirch heralded the birth of Edward Teach, also known as Blackbeard, the most notorious pirate of all time. Exiting life on Earth that year was Colonel Thomas Blood, who had stolen the English Crown Jewels in 1671, and almost got away with them. Luckily for him, King Charles II had a love of scoundrels, so Colonel Blood got a royal pardon.

McNaught

The Great Comet of 2007 was the 31st comet discovered by modern-day asteroid and comet hunter Robert McNaught. We are so lucky to live in an age when we can not only appreciate such wonders as Comet McNaught with our own eyes but there is the technology to photograph them and the means to distribute the images worldwide so others who weren't so lucky can appreciate them too. At its most photogenic, the luminous bands of its tail spanned some 35° of the southern skies. We can only imagine whether the 18th-Century 'comet ferret' Charles Messier would have been satisfied with digital imagery if it had been available to him.

Shoemaker-Levy 9

Comet Shoemaker-Levy 9 ensured its place in history with its extraordinary death. It was discovered in March 1993 in orbit around Jupiter by astrogeologist Dr Eugene 'Gene' Shoemaker, his wife Carolyn and their friend David Levy. Astronomers knew that the comet was being pulled apart by Jupiter's gravity and that the fragments would eventually impact the gas giant. Never before in history had such an event been witnessed, so Jupiter was monitored 24/7 until, between 16-22 July, 1994, chunks of the comet punched Jupiter's atmosphere like a crashing wagon train, leaving visible 'bruises' the size of the Earth. That was the end of comet Shoemaker-Levy 9, but what a way to go!

• Co-discoverer of the Jupiter-collision comet Gene Shoemaker was killed in a car accident while visiting impact craters in Australia exactly three years later, on 18 July, 1997. Uncannily, or perhaps significantly, Comet Hale-Bopp was still visible on that date. A memorial capsule containing some of his ashes was launched with NASA's Lunar Prospector space probe. Following completion of its mission, the probe was allowed to impact the Moon's surface. To date Shoemaker is the only human being whose remains rest on another world.

Tempel-Tuttle

The comet 55P/Tempel-Tuttle was named after Wilhelm Tempel (1821 – 1889) and Horace Parnell Tuttle (1837 – 1923) who co-discovered it upon its return to the inner Solar System in 1866. Modern astronomers have been able to backtrack the 33-year periodic comet to its first recorded appearance in 902 AD. While this particular comet doesn't have the charisma of the diva celestial visitors, it is the one which is responsible for our annual Leonid meteor shower. This is a hotly-anticipated meteor shower during years when the comet revisits, as it deposits more debris in its wake. This then falls as 'shooting stars' when the Earth travels through the comet's orbital path. One descriptive writer, Agnes Mary Clerke, shared her experience about what happened on the night of 12-13 November, 1833:

A tempest of falling stars broke over the Earth... The sky was scored in every direction with shining tracks and illuminated with majestic fireballs. At Boston, the frequency of meteors was estimated to be about half that of flakes of snow in an average snowstorm. Their numbers were quite beyond counting; but as it waned, a reckoning was attempted, from which it was computed, on the basis of that much-diminished rate, that 240,000 must have been visible during the nine hours they continued to fall.

Comet Tempel-Tuttle will pass our way again in 2031. We can only cross our fingers and hope that the Leonid meteor shower that year will be half as spectacular!

West

Comet West travelled within 0.2 AU⁵ of the Sun and subsequently the nucleus broke into four chunks. It was visible in broad daylight post-perihelion in early March 1976, and from dark skies it looked like a multi-coloured cosmic feather. Comet West's orbital path is a mind-boggling length; so far that astronomers measure it as one light year. As comets don't travel at the speed of light, Comet West won't be back this way any time soon, probably not for a million years. We wonder what changes will have occurred on Earth in that time and whether human beings will even be around to witness its second appearance, what with things like Comet Swift-Tuttle⁶ being placed on the list of potentially threatening NEOs (near-Earth objects) at NASA's Jet Propulsion Laboratory.