What's the difference between a comet and a mass?

Classification: education/study/examination >> National College Entrance Examination

Analysis:

Comet (comet)

The main body of a comet is mainly composed of frozen gas and dust, so it has the title of "dirty snowball". Its diameter is usually only a few kilometers, and when it exceeds 10 kilometers, it is very huge, and its orbit is mostly oblate or parabolic. The former circled the sun for several years to tens of thousands of years, while the latter visited the sun once and never came back. Usually comets are frozen because they are far away from the sun, and their luminosity is extremely dim. However, as soon as they enter the earth's orbit and the distance from the sun is shortened, they will start to be lively, and at the same time release a lot of dust to form coma and tail. The volume is very huge, and the largest can even be compared with the sun, but its density is thinner than the "vacuum" that can be created on the earth.

Great comets visible to the naked eye do not often appear, but there are more than twenty comets that can be observed by telescope or photography every year. If spectacular and bright comets occasionally appear, it will cause a huge astronomical upsurge, such as Comet Wu Bai and Comet Haier in previous years. Popper's comet is, except for Halley's comet, which has a period of 76 years, almost all aperiodic comets that can attract public attention (referring to comets with a period of more than 200 years or will not return); In May, 2004, it is estimated that two large comets with brightness above 1 will appear in the western sky at the same time after sunset. This rare astronomical spectacle is worth looking forward to.

Meteor (meteor)

Meteors are mainly dust particles roaming in space, some of which are so small that they can't even be seen by the naked eye. They are attracted by the gravity of the earth and fall to the earth. They usually enter the earth's atmosphere at the speed of 1 1~7 1 km per second, and the high heat generated by friction with the atmosphere is enough to make themselves evaporate and disappear, and the electrons are excited to emit light, with a luminous height of about 80 km. A meteoroid with a large mass, or a large meteor with brightness above -2, is usually called a "fireball" or "fireball". Some of them will be greatly brightened by the explosion in the middle, and sometimes even sound can be heard. Some bright meteors will leave faint meteor traces after passing by, while larger meteors can last for a few minutes, and then slowly disperse and disappear with the strong wind at high altitude.

We can often see a few scattered meteors flying over lonely nights in ordinary nights, but in addition to these random meteors, sometimes there will be a large number of meteors (more than dozens per hour) in a short time, and they all fly out from the same radiation point, which is what we call "meteor shower"; Meteor showers occur when the earth passes through the dust left by a group of comets. Comets that can cause meteor showers must intersect the earth in orbit, so we often say that comets are the mother of meteors. Every year, the earth passes through some meteor groups regularly, forming a meteor shower.

Among them, the most famous meteor showers are quadrant meteor shower, Perseid meteor shower, Leonid meteor shower and Gemini meteor shower. The naming method of meteor shower usually depends on the location of radiation point. The number of meteors per hour (ZHR) usually ranges from a few to hundreds, and sometimes there is a rare phenomenon of "star rain". The number of meteors per hour can reach 1000 or even dozens. Among them, the most famous Leonid meteor shower has a maximum cycle lasting for several years every 33 years, and it is very likely that there will be a meteor shower at the maximum.