Disintegrate the "comet of doomsday" or usher in the end before the most dazzling moment

Recently, a news about the brightest comet in 2020 or its disintegration caused quite a stir.

  Speaking of this comet, but the beginning is not small, as early as the beginning of March, the name of "the end of the comet" has been spread among astronomy enthusiasts.

  "The Doom Comet" is actually a comet named C / 2019 Y4. As we approached the earth, amazing news about it appeared frequently: Some people said that according to computer simulations, this comet can reach the brightest level of -24.7, making it the brightest star in the sky, but some people think that its brightness is not Not as high as imagined.

  At first, in order to attract attention, some people gave it such a bullish name on the Internet, but it never happened that on the way to the earth, it suddenly fell apart and became a real "come of doomsday." At present, its brightness has dropped to 8.8-9.2, etc., it is likely that it will continue to decline in the future until it cannot be seen.

  Why is there such a big deviation in the calculation of comet brightness? What was the brightest comet before? C / 2019 Will Y4 split fragments hit the earth? In response, Shi Jianchun, an associate researcher at the Purple Mountain Observatory of the Chinese Academy of Sciences, was interviewed by a reporter from Science and Technology Daily.

  The super bright comet is exciting

  Comets are a very special type of celestial body in the solar system. In the comet family, we are most familiar with the "Harley Comet". In fact, since the 21st century, the night sky in the northern hemisphere has never ushered in a larger comet.

  Most people's understanding of comets may only stay in books and have not seen it with their own eyes, but this regret is likely to be compensated in the next few months.

  Comet C / 2019 Y4 was discovered by Atlas-Asteroid Ground Impact Warning System on the evening of December 28, 2019, and was the last comet discovered in 2019, so some people call it Atlas comet.

  Atlas was located in the constellation Ursa Major, with a magnitude of 19.6, 2.46 astronomical units from the earth (one astronomical unit is about 150 million kilometers), and 2.94 astronomical units from the sun. According to calculations, Comet Atlas will be too close to the ground on May 23, 2020, at that time it was only 0.78 astronomical units from the earth, and passed the perihelion on May 31, 0.25 astronomical units from the sun, at this time 0.87 astronomy unit.

  Although the brightness of Comet Atlas was not high at the time of discovery, the magnitude was only 19.6, but it is speculated that it will reach its maximum brightness when it is closer to the sun in late May.

  Generally, people call the brightness of the celestial body seen with the naked eye as the apparent magnitude. The apparent magnitude is related to the luminous ability of the celestial body and the distance between the celestial body and the observer. The higher the brightness, the lower the magnitude of the celestial body. A very bright celestial body may appear very dark because it is too far away from the observer; and an actually very dark celestial body may appear very bright because it is closer to the observer.

  After being discovered, the comet immediately showed great strength. From the first discovery to February this year, the comet has brightened nearly 8 magnitudes, increasing from the original 19.6 magnitude to 12.3 magnitude, the brightness increased by more than 800 times.

  According to previous media reports, according to computer simulations, the comet ’s visual brightness will reach -24.7 when its brightness is at its maximum. what is this concept? You know, the brightness of the sun is only -26.8. This brightness may make people unable to look directly. If you see this comet at night, the city ’s lights and neon lights will be eclipsed in front of it, obviously contrary to common sense.

  Although not as bright as the sun, according to predictions, astronomers in the northern hemisphere can still see the comet with the naked eye before sunrise when it reaches the perigee. After a few years of "empty window period", a large comet visible to the naked eye seems to be passing the earth, giving a gift to astronomy enthusiasts.

  The shoulder-to-shoulder sun is actually an oolong

  Why did comet Atlas shine above the sun for a while? For a while, only visible to the naked eye? What determines the brightness of a comet?

  The comet is mainly composed of water ice, gas ice and dust. It does not emit light itself. The light we see is the sunlight reflected by the comet material. Due to the difference in the composition of different comets, different comets exhibit different colors.

  In the early days, the brightness value of comet Atlas was unreasonably high, which caused many people to question. Later, some forecast models were calculated after re-correcting the parameters, and it is conservatively estimated that Comet Atlas may still reach between 2 and 5 between the end of May and the beginning of June.

  "Scientists predict that the comet's brightness is mainly based on the comet's orbit and the brightness, heliocentric distance, geocentric distance, phase angle and other parameters before the comet." Shi Jianchun told reporters.

  Generally speaking, although different models have different predictions of brightness, the difference should not be too large.

  Shi Jianchun believes: "The reason why the predictions of different models are quite different may be related to the sample data on which the different models predict the future brightness of the comet. There is an accident here. For example, the brightness sample taken by a model happens to be a comet. At the outbreak stage, then it will have a large error in estimating the brightness of the comet. "

  At present, the brightest comet discovered by mankind is the comet Igutani-Kuan (C / 1965 S1) discovered in 1965. Its brightness reached -10 on October 21 of that year, which is about twelve points of the brightness of the full moon. one.

  The change in comet brightness is related not only to the aforementioned heliocentric distance, geocentric distance, and phase angle, but also whether the comet has an explosion event.

  Shi Jianchun said that during the approach of the comet to the sun, the internal ice sublimates under the action of the sun's heating, which in turn brings out the internal dust, forming the "coma" and "comet tail" we see. Under normal circumstances, the increase of the comet's brightness is a gradual process, but sometimes the comet is also interfered by other factors to cause an explosion. The explosion refers to the comet ejecting a large amount of material in a short time, causing the comet's brightness to increase sharply. process. But after the explosion, the brightness of the comet will return to near the original level.

  "From the brightness information of the comet, we can know the size, rotation period, composition, and activity level of the comet." Shi Jianchun said.

  "The most shining star" or Xiang Xiao Yu Yu die

  March was full of expectations, and it fell to the bottom in April.

  Atlas comet has brought surprises to astronomy fans around the world, but before it was time to celebrate, the bad news suddenly struck.

  In early April, someone published three observations. It was originally expected that it will continue to brighten, but there are some signs of recession. Many people think this is a bad sign.

  Until April 6, the brightness of Comet Atlas decreased significantly. Based on various observations, it is speculated that the core of Comet Atlas is elongated, and it seems to be disintegrating!

  "Comet Atlas just split on April 6 and split into at least 4 pieces. Its brightness is also 6 times lower than previously expected. Therefore, it remains to be seen whether the brightness of this comet can continue to increase. Shi Jianchun told reporters.

  According to his analysis, the cause of the split of Atlas comet may be due to the degassing effect of the comet, which caused the acceleration of rotation and the increase of centrifugal force, which exceeded its own gravity and tensile strength, resulting in splitting.

  The "brightest star" in the sky is broken, and the hearts of many astronomy lovers are also broken. But some people worry that this "dome comet" will really bring "doom" to the earth? Where will the comet fragments fly? Will it hit the earth?

  "At present, this is not possible." Shi Jianchun analyzed that most of the decomposed fragments of the comet are still in their original orbits due to inertia. "A slight deviation may occur, but it will not be too large. The orbit of Comet Terras is also 110 million kilometers when it is closest to the earth, which is equivalent to 300 times the distance between the earth and the moon, and will not hit the earth at all. "

  At present, the brightness of Comet Atlas has been lower than 10, and it is likely that it will continue to decline until it cannot be seen. Scientists believe that it may completely disintegrate before it reaches perihelion.