Why are some of the stars in the sky bright and some dark?

There are two main factors that determine whether people observe the stars as light or dark:

One is due to the size of the star's ability to emit light, and the other is the distance between the star and people.

Astronomers usually divide the ability of stars to shine into 25 magnitudes, with the strongest ones being about 10 billion times different from the worst ones.

A star that is close to people has a strong ability to emit light, so people will light up when they see it. However, even if a star is quite capable of emitting light, if it is very far away, then its brightness may not be as bright as that of a star that is tens of thousands of times less capable of emitting light.

1 Some stars are near and some are far away 2 Inhomogeneity due to the existence of the earth's atmosphere and changes in air currents 3 The intensity of the light emitted varies due to the different states of each star 4 Generally, because the planets in the solar system are relatively close to the earth, they can be seen by the naked eye by reflecting the sun's light. Planets outside the solar system are generally invisible to the naked eye because they do not emit light. The stars we usually see are stars 5 The light of the star we see is actually emitted by this star a long time ago.

The brightest is the "zeroth" and the "sixth" is dark, which allows us to see with the naked eye; More are stars above the "seventh magnitude". It is now stipulated that for every 1st magnitude difference between stars, the brightness of a star of the 1st magnitude is exactly equal to 100 times that of a 6th magnitude star. ]

One of the reasons for determining the brightness of a star is its ability to emit light, which varies by a factor of 10 billion in size. Another reason is the distance between the stars and us, and generally speaking, the closer the stars are to us, the brighter they become.

The size of the stars is another case, large stars do not necessarily shine very strongly, and some stars that appear to be faint are often huge stars.

The brightest known star, up to 1 million times the luminosity of the Sun; The smallest star is only one millionth of the luminosity of the Sun. In astronomy, stars with low luminosity are called dwarf stars, stars with large luminosity are called giants, and stars with particularly large luminosity are called supergiants.

To compare the true luminous power of stars, astronomers use absolute magnitude to indicate the luminosity of stars. That is, put different stars at the same distance for comparison. It's like a race, standing on the same starting line.

The star's "starting line" is defined at a distance of 10 parsecs (light-years) from the observer. The brightness observed at this distance is expressed in absolute magnitude.

The two bright stars in the sky are Venus and Jupiter.

Venus and Jupiter are the closest together, Venus is the brightest star in the sky, and Jupiter is second only to Venus in brightness.

The low is Venus and the high is Jupiter. Venus is particularly bright because of its close proximity and its strong ability to reflect light. Venus can reach at its brightest and so on.

Jupiter is large and reflective, and Jupiter is above magnitude 2 at its brightest. They are the brightest stars in the sky, and both are brighter than Sirius. Sirius has only waiting.

Geographical features. The sky of Venus is orange-yellow. There was also thunder and lightning on Venus, with the largest ever recorded flash ridge of lightning lasting 15 minutes.

Venus's atmosphere is mostly composed of carbon dioxide and contains small amounts of nitrogen. The atmospheric pressure of Venus is very large, 92 times that of the Earth, which is equivalent to the pressure in the Earth's oceans at a depth of 1 kilometer. The presence of a large amount of carbon dioxide makes greenhouse dry on a large scale on Venus.

Without such a greenhouse effect, the temperature would drop by 400 .

01 Stars are generally stars that emit light by themselves, and the brightness and darkness of the stars seen by the naked eye are mostly related to the size and distance of the stars. For example, the stars of Cowherd (Aquila) and Weaver Girl (Lyra) are not as bright as the moon, but they are actually much larger and brighter than the sun, and they appear dark because they are far away from the earth.

The stars in the sky are some bright and some are dark. We know that a 60-watt lamp is brighter than a 20-watt lamp because of its ability to emit light. So, do bright stars shine more than dark stars?

In fact, this is not necessarily the case, in addition to its ability to shine, there is another reason that determines the brightness of the star, which is the distance between the star and us. Generally speaking, the closer the stars are to us, the brighter they look. The above is the apparent brightness of the star, which is the brightness of what it seems.

Apparent brightness is expressed in terms of apparent magnitude. The brightest stars we see are generally classified as 1st magnitude, and the faintest stars that people with normal vision can barely see with the naked eye are classified as 6th magnitude. A bright star in the sky may really be a star that emits a lot of light, but it may also be bright just because it's so close to us.

Conversely, some faint stars are not necessarily dim, and although they can only be seen through telescopes, they may be extremely capable of emitting light, but they appear faint because they are so far away from us.

In order to compare the true luminous power of different stars, they should be compared at the same distance as us. It's like a race, you have to stand on the same starting line and start at the same time. According to international regulations, this "starting line" of the star is set at 10 parsecs, that is, light years.

The brightness of a star at this standard distance is specified as its absolute brightness, which is expressed by absolute magnitude. Athletes can start on the same starting line, and stars can't all move to a distance of 10 seconds, so absolute magnitude is calculated. The apparent brightness of the Sun is the absolute champion, and once it is placed at a distance of 10 parsecs more than 2.06 million times farther than it is now, its absolute magnitude is only +.

The following five celestial bodies in apparent magnitude order should be inverted if they are arranged in absolute magnitude.