Moscow Planetarium logo.
May 4, 2021
Most comets that fall into the region of the solar space are not bright enough for an observer on Earth to see them with the naked eye. Therefore, they are noticed only by astronomers with the help of telescopes.
Image above: Comet Hyakutake in the night sky at its closest approach to Earth on March 25, 1996.
When comets become bright enough to be clearly visible from Earth without special instruments, they are called Great or Great comets. However, there is no official definition of the term "Big Comet". For a comet to become Large, a combination or presence of one of the following factors is necessary:
- The comet must have a large and active nucleus;
- The comet must be close to the sun;
- The comet must be close to Earth.
A comet that meets all of these criteria will be extremely bright and spectacular. But even if at least one of them is triggered, the comet will also be visible to the naked eye. In March 1996, the small comet Hyakutake (C / 1996 B2) passed relatively close to the Earth (15, 2 million km), therefore it was easily observed with the naked eye in the night sky, due to which it was named the Big Comet of 1996.
Image above: Comet Hale-Bopp. Photo near the city of Pazin (Croatia), March 29, 1997.
Comet Hale-Bopp (C / 1995 O1) did not come very close to the Sun, like many other comets, but it had a very large and active core with a diameter of more than 40 km, so it became one of the most observed comets of the 20th century. Experts studied it for 18 months in 1995-1997. At perihelion passage on April 1, 1997, the comet was a stunning sight. Then they began to call it the Big Comet of 1997.
A comet that approaches the Sun at a distance of less than 75 million km can potentially become a Large comet, even having a small nucleus. If this event coincides with the comet's proximity to Earth, the effect will be more dramatic.
Image above: Comet McNaught. Sydney, Australia, January 19, 2007.
Comet McNaught (C / 2006 P1), also known as the Big Comet of 2007, having a core diameter of about 25 km, but passing from the Sun at a distance of only 25.5 million km, became the brightest comet since the 1965 Ikei-Seki comet.
It is difficult to predict whether comet Big will become. For example, comet Kogoutek 1973, according to all calculations, should have become very bright and spectacular. In the media, it was even called "the comet of the century." But, approaching the Earth, she turned out to be rather pale and uninteresting, for which she was nicknamed "Comet Watergate".
Related article:
Main belt comets
https://orbiterchspacenews.blogspot.com/2021/03/main-belt-comets.html
Related links:
ROSCOSMOS Press Release: https://www.roscosmos.ru/30959/
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.
Best regards, Orbiter.ch
