Comet

A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail.

The word ‘comet’ came originally from a Greek word ‘comitis’ meaning ‘wearing long hair’.

Most comets are believed to originate in a cloud (the Oort cloud) at large distances from the Sun consisting of debris left over from the condensation of the solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state.

Not long after Julius Caesar was assassinated, a comet shone for seven successive days. Caesar's Comet, which was interpreted by Romans as a sign of the deification of their recently murdered dictator, was perhaps the most famous comet of antiquity.

This signified Julius Caesar's ascension to Godhood, and propaganda for Caesar's nephew. The comet was described as: "To make that soul a star that burns forever, Above the Forum and the gates of Rome."

Arthur Storer, America's first colonial astronomer, was among the first observers to sight and record data about a magnificent comet that passed over Patuxent skies in 1682. The comet became known as Storer's Comet, until English astronomer Edmund Halley later predicted the comet's return; thereafter this celestial marvel was known as Halley's Comet.

Halley's Comet

Halley claimed in 1705 that several comet sightings — dating from 1531, 1607 and 1682 — related to a single comet whose orbit brought it past Earth every 76 years. Sadly, he died before the comet’s return around Christmas in 1758 proved him correct.

The first recorded perihelion passage of Halley's Comet was in 240BC.

Halley's Comet and Earth experienced their closest approach to one another in 837 AD when their separating distance equaled 0.0342 AU (3.2 million miles).

Halley's Comet blazed across the sky on April 24, 1066 and the week that followed. It was a very bright comet, and it was visible to the naked eye in the daytime sky. Many people in Europe saw the comet, and it was interpreted as a sign of bad luck or impending disaster. In fact, the comet appeared just a few weeks before the Battle of Hastings, in which William the Conqueror defeated King Harold and took the English throne. Some people believe that the comet was a sign of William's victory, while others believe that it was simply a coincidence.

The comet's appearance in 1066 was recorded on the Bayeux Tapestry

German astronomer Gottfried Kirch discovered the Great Comet of 1680 on November 14, 1680 in Coburg. It was the first to be found using a telescope. The Great Comet of 1680 became one of the brightest comets of the 17th century – reputedly visible even in daytime – and was noted for its spectacularly long tail.

Lexell's Comet passed closer to the Earth than any other comet in recorded history, approaching to a distance of 0.015 AU (2,200,000 km; 1,400,000 mi) on July 1, 1770. The comet has not been seen since 1770 and is considered a lost comet.

The comet was named after the Swedish astronomer Anders Johan Lexell, who calculated its orbit and predicted its close approach to Earth. Lexell's Comet had a highly elliptical orbit, and its close encounter with Earth caused it to be visibly bright in the night sky. It was even visible to the naked eye for several months.

After its close approach, Lexell's Comet moved away from Earth and has not been observed since. It is considered a "lost comet" because its orbit hasn't been accurately determined since its 1770 appearance. Several attempts have been made to locate the comet, but so far, none have been successful.

Jean-Louis Pons was a French astronomer who made a total of 37 comet discoveries between 1801 and 1827. His first comet discovery was on July 11, 1801, and it was jointly attributed to Charles Messier. Pons was a self-taught astronomer who began his career as a doorkeeper at the Marseille Observatory. He was eventually given lessons in astronomy by the directors of the observatory, and he went on to become one of the most successful comet discoverers in history.

Jean-Louis Pons

American astronomer Edward Emerson Barnard discovered D/1892 T1, the first comet found by photographic means, on the night of October 13, 1892.

Edward Emerson Barnard

Samuel Clemens (Mark Twain) was born on and died on days when Halley's Comet could be seen. He predicted he would die when it was visible.

The Hale–Bopp comet was discovered independently on July 23, 1995 by two observers, Alan Hale and Thomas Bopp, both in the United States. When amateur astronomer Thomas Bopp co-discovered Hale–Bopp, he had never seen a comet before and was using a borrowed telescope.

As Hale–Bopp passed closer to Earth, it became the most widely observed comet of the 20th century and one of the brightest seen for many decades. It was visible to the naked eye for a record 18 months, twice as long as the previous record holder, the Great Comet of 1811.

Image of Hale-Bopp, taken on 1997 April 04, By E. Kolmhofer, H. Raab; 

When Hale–Bopp was discovered at a great distance from the Sun,  there were expectations that the comet would brighten considerably by the time it passed close to Earth. Although predicting the brightness of comets with any degree of accuracy is very difficult, Hale–Bopp met or exceeded most predictions when it made it closest approach to The Sun on April 1, 1997.

The Philae is a robotic European Space Agency lander that accompanied the Rosetta spacecraft. On November 12, 2014 it landed on Comet Churyumov–Gerasimenko, the first-ever controlled touchdown on a comet nucleus.

Depiction of Philae on Churyumov-Gerasimenko. By DLR, Wikipedia

C/2014 Q2 (Lovejoy), a comet discovered in August 2014 and visible to the naked eye in December 2014 and January 2015 was known to release alcohol into space. It gave off enough alcohol to produce 500 bottles of wine per second.

Comet tails are created by an interaction with either solar winds or photons from the sun. The tail always points away from the sun.

The tail of a comet is formed of dust and ice, blown by solar winds as the ice melts.

The Perseid meteor shower, which is seen from Earth every August, occurs when the Earth passes through the orbit of the Swift-Tuttle comet.

You are ten times more likely to be hit by a comet than to die in a plane crash.

Source Daily Express