What type of comet is halley comet

Halley's orbit period is, on average, 76 Earth years. This corresponds to an orbital circumference around the Sun of about 7. The period varies from appearance to appearance because of the gravitational effects of the planets. Measured from one perihelion passage to the next, Halley's period has been as short as The comet's closest approach to Earth occurred in , at a distance of 0.

At that time, April 10, , Halley reached a total apparent brightness of about magnitude The light of Halley was spread over an extended area, however, so its surface brightness was less than that of Venus. During its appearance, Halley's nearest approach to Earth occured on the outbound leg of the trip at a distance of 0.

It was slightly brighter than the north star Polaris, but again spread over a much larger area than a point-like star. At aphelion in , Halley was The comet was moving 0. At perihelion on February 9, , Halley was only 0. Halley was moving at , mph With each orbit around the Sun, a comet the size of Halley loses an estimated 3 to 10 feet 1 to 3 meters of material from the surface of its nucleus.

Thus, as a comet ages, it eventually dims in appearance and may lose all the ices in its nucleus. The tails disappear at that stage, and the comet finally evolves into a dark mass of rocky material or perhaps dissipates into dust. Scientists calculate that an average periodic comet lives to complete about 1, trips around the Sun. Halley has been in its present orbit for at least 16, years, but it has shown no obvious signs of aging in its recorded appearances.

The letter "P" indicates that Halley is a "periodic" comet. Halley's most famous appearance occurred shortly before the invasion of England by William the Conqueror. It is said that William believed the comet heralded his success. In any case, the comet was put on the Bayeux Tapestry — which chronicles the invasion — in William's honor. Astronomers in these times, however, saw each appearance of Halley's Comet as an isolated event.

Comets were often foreseen as a sign of great disaster or change. Even when Shakespeare wrote his play "Julius Caesar" around , just years before Edmond Halley calculated that the comet returns over and over again, one famous phrase spoke of comets as heralds: "When beggars die there are no comets seen; The heavens themselves blaze forth the death of princes.

Astronomy began changing swiftly around the time of Shakespeare, however. Many astronomers of his time held that Earth was the center of the solar system, but Nicolaus Copernicus — who died about 20 years before Shakespeare's birth — published findings showing that the center was actually the sun.

It took several generations for Copernicus' calculations to take hold in the astronomy community, but when they did, they provided a powerful model for how objects move around the solar system and the universe.

The comet appeared in , and Halley suggested the same comet could return to Earth in Halley did not live long enough to see its return — he died in — but his discovery inspired others to name the comet after him. On each successive journey to the inner solar system, astronomers on Earth turned their telescopes skyward to watch Halley's approach.

The comet's pass in was particularly spectacular, as the comet flew by about On that occasion, Halley's Comet was captured on camera for the first time. It is coming again next year, and I expect to go out with it. When Halley's Comet came by Earth in , it was the first time we could send spacecraft up to look at it. That was a fortunate occurrence, as the comet ended up being underwhelming in observations from Earth.

When the comet made its closest approach to the sun, it was on the opposite side of that star from the Earth — making it a faint and distant object, some 39 million miles away from Earth.

Several spacecraft successfully made the journey to the comet. This fleet of spaceships is sometimes dubbed the "Halley Armada. However, subsequent observations have indicated that this is unlikely. Whereas King Harold of England saw the comet as a bad omen, William and his forces interpreted it as a sign of their impending victory at least according to legend.

Throughout the Middle Ages, the appearances of comets in the night sky were seen as heralds of bad news, indicating that either a person of royal standing had died, or that dark days lay ahead. This is perhaps owing to what was seen as the erratic and unpredictable behavior of comets, when compared to the Sun, the Moon and the stars. With the development of modern astronomy, this view of comets has been largely dispelled. In , David C. Jewitt conducted a study that indicated that Halley will likely evaporate, or split in two, within the next few tens of thousands of years.

Alternately, Jewitt predicted that it could survive long enough to be ejected from the Solar System entirely within a few hundred thousand years.

Meanwhile, observations conducted by D. Hughes et al. By their estimations, it would not be surprising at all if the comet evaporated entirely within the next revolutions or so approx. As always, some are choosing to prepare for the worst — believing its next pass will signal the end of life as we know it — while others are contemplating if they will live long enough to witness it.

Astronomy Cast has an episode on comets. Could a crater have formed from some impact?