Halley's Comet
Halley's Comet, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years. This periodicity was first recognized by the English astronomer Edmond Halley in 1705, who used Newtonian physics to predict its return in 1758, after its previous sighting in 1682. Halley's prediction was confirmed when the comet was observed again, and it was named after him posthumously.
Historical Observations
- The earliest known sighting of Halley's Comet was recorded in 240 BC by Chinese astronomers.
- It has been observed and recorded by various cultures throughout history, including the Chinese, Babylonians, and Europeans.
- In 1066, the comet's appearance was famously depicted in the Bayeux Tapestry where it was seen as an omen before the Battle of Hastings.
- Notable apparitions include those in 1531, 1607, 1682, 1835, and 1910.
- The 1910 appearance was particularly notable as Earth passed through the comet's tail, causing widespread public fear due to misinformation about the effects of the comet's gases.
Characteristics
Halley's Comet has an elliptical orbit that takes it from the outer reaches of the solar system to the inner solar system. Here are some key characteristics:
- Its nucleus is relatively large, about 15 kilometers in diameter.
- The comet's orbit is retrograde, meaning it moves around the Sun in the opposite direction to most other bodies in the solar system.
- When close to the Sun, the comet's ice sublimates, forming a bright coma and two tails: a dust tail and an ion tail.
- Its orbital period varies slightly due to gravitational perturbations by planets, especially Jupiter.
Modern Observations
The most recent appearance of Halley's Comet was in 1986. Due to its distance from Earth during that apparition, it was not as spectacular as previous sightings:
- The European Space Agency's Giotto mission flew by the comet and provided detailed images and data about its nucleus.
- In 1986, the comet was only at a distance of about 63 million kilometers from Earth, much farther than in 1910.
- It is expected to return in the year 2061.
Impact on Culture and Science
Halley's Comet has had a profound impact on both science and culture:
- It helped establish the science of celestial mechanics, confirming theories about the orbits of comets.
- The comet's appearances have often been interpreted as omens or signs, influencing art, literature, and historical events.
- The study of Halley's Comet has contributed to our understanding of the solar system's formation and the role of comets in delivering water and organic compounds to Earth.
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