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August 29, 2021
As it approaches the Sun, the comet begins to glow. A coma forms around its core - a light bowl-shaped shell and a glowing tail that can stretch for millions of kilometers. Sometimes, however, comets flare up so brightly that it baffles scientists. Comet Holmes belongs to such objects.
Comet Holmes (17P / Holmes) was discovered by British amateur astronomer Edwin Holmes. The period of its revolution around the Sun is about seven years. On November 6, 1892, while observing the Andromeda Nebula galaxy, Holmes discovered an object with a brightness of about five magnitudes, which turned out to be a comet. The comet's brightness continued to increase and reached three magnitudes by the end of November. In December, it began to fade and was no longer visible to the naked eye.
Image above: Holmes' comet. Snapshot November 4, 2007. Holmes' comet. Snapshot November 4, 2007.
Later, Holmes's comet was observed in 1899 and 1906, then it was lost and rediscovered by the American astronomer Elizabeth Roemer only in 1964, after which it was observed regularly. In 2007, after passing the perihelion in early May, the comet gradually faded from 14.0 m to 17.0 m. This continued until October 25, when an unexpected outburst on the surface of the comet in just a few days increased its brightness to three magnitudes (it became brighter almost half a million times). This outburst was the largest in the history of cometary observations.
Until the end of October, the comet could be observed as a bright yellow star in the constellation Perseus, the third brightest among all the stars in the constellation. In November, observers reported slight extinction of the comet, while the size of the coma continued to increase. The comet was visible until the end of February 2008. Based on calculations of the comet's orbit and brightness made before the 2007 outburst, the diameter of its core is approximately 3.4 km. A similar flash of brightness up to four magnitudes occurred in January 2015, but then the comet was too far away, and it could only be observed through a powerful telescope.
Image above: The position of the comet in the sky from October 25, 2007 to March 9, 2008. The position of the comet in the sky from October 25, 2007 to March 9, 2008.
The data obtained from various sources around the world still do not allow us to understand the nature of the mysterious processes taking place on the comet. Some researchers believe that a giant luminous cloud of dust and gas could have appeared when a comet collided with an asteroid, but many comets pass through the asteroid belt without any consequences. Holmes's comet, according to this version, should have collided with asteroids three times, which is unlikely. Perhaps the anomalous brightness is associated with explosions of gas vapors under the influence of sunlight, but the comet explodes each time not at perihelion, but much further. The symmetry of the cloud formed after the explosion is also puzzling. Scientists still do not have a clear answer to these and many other questions.
Source: Moscow Planetarium.
Related links:
ROSCOSMOS Press Release: https://www.roscosmos.ru/32333/
Moscow Planetarium: https://www.roscosmos.ru/tag/moskovskiy-planetariy/
Comet: https://www.roscosmos.ru/tag/kometa/
Images, Text, Credits: ROSCOSMOS/Moscow Planetarium/Orbiter.ch Aerospace/Roland Berga.
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