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Delights at night

By Zhang Lei | China Daily | Updated: 2020-08-01 16:49

Star chasers hold their breath when Neowise appears in the northwestern sky after nightfall.[Photo by Bai Jikai/For China Daily]

In just over half a month, its brightness increased about 100 times. Why does the brightness change drastically? In fact, the main reason is the distance between the comet and the sun.

The comet can be seen by us because it reflects the sunlight. On the one hand, as the comet approaches the sun, the intensity of the sun's light continues to increase, so it looks brighter and brighter. On July 3, Neowise reached perihelion, only about 43 million kilometers away from the sun, so it would shine.

On the other hand, the comet continues to accelerate, causing dust tails to stretch longer. Therefore, when the comet gets closer to the sun, it looks brighter. The energy of the sun heats the comet, and gas and dust erupt from the surface of the comet, forming a huge dust tail, usually in yellow. At the same time, the comet produces a stream of charged particles under the action of the solar wind, forming an ion tail, which is generally blue.

In mid-to-late July, due to the orbital movement, the majority of star chasers have a higher probability of seeing this comet in the evening and dawn. In order to observe it more before it gradually moves away, Li drove to Inner Mongolia three times in a week, persistently recording its dreamlike light with a camera. According to the calculations of some star chasers, the next time we see this comet from Earth will be in 6,800 years.

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