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Mystery of the universe: what is a bright nebula?

What is a bright star cloud?

1694, a scientist saw and described a bright fuzzy area in Orion, which looked like a glowing cloud and was later called a nebula. Now, we call it the Orion Nebula. This is a bright star cloud, a huge cloud of dust and gas, about 30 light-years wide. If we put the whole solar system, from the sun to the farthest comet, into the Orion nebula, the solar system will disappear into the infinite space of the nebula, and even the sun and its nearby 12 stars can be easily accommodated.

A bright nebula is a brighter nebula. It is bright because this nebula contains stars, because the nebula itself does not emit light. For example, the Orion Nebula contains many stars that excite hydrogen and make it emit green light. It is 300 light-years in diameter, but only a small part of the diameter of 27 light-years is illuminated by the nebula and seen by us, but this part is too big for us humans. In fact, in general, according to the different ways of light emission, it can be divided into emission nebula (there is a very hot star in the middle of the nebula, and the nebula absorbs the ultraviolet radiation of this star before emitting visible radiation) and reflection nebula (reflecting the bright nebula nearby).

Wanderers in the sky

Planets are celestial bodies that revolve around the sun or other stars (except comets, meteors or satellites). The eight planets revolving around the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The planet itself does not shine, but because the surface reflects sunlight. It has color characteristics and brightness changes. It is hidden among the stars, advancing and retreating freely, and people call it a celestial body wandering in the sky. Planets can be classified in different ways. With the earth's orbit as the boundary, the planets in the earth's orbit are called inner planets, such as Mercury and Venus. Jupiter, Saturn, Uranus, Neptune and Pluto outside the earth's orbit are called extraterrestrial planets; With the asteroid belt as the boundary, Mercury, Venus, Earth and Mars near the sun are called inner planets, while Jupiter, Saturn, Uranus, Neptune and Pluto far away from the sun are called outer planets. There are also terrestrial planets, such as Mercury, Venus, Mars and Earth, which are classified according to their mass. Other stars (except Pluto) are similar to Jupiter and are also called woody planets. Observations in recent years show that planets may not be unique to the solar system, and other stars outside the solar system may also have planetary systems.