How to measure sidereal time at night Are all the stars you see at night star?

There are more than a dozen ways to measure the distance of a star, and you can take two lessons, and you can't explain it clearly in a few words. To put it simply, some of the closest stars to us can use the method of trigonometric parallax to measure the position of the stars separately in half a year, and for the stars close to us, it can be found that there is a displacement, which is parallax, known the parallax angle and the radius of the Earth's orbit around the sun, and the stellar distance can be calculated with a triangular relationship. This is the most accurate method, but for slightly farther stars, the parallax angle is too small to measure, and it will not work.

For example, for some variable stars, the light period is related to the intrinsic brightness of the star, and the apparent brightness of the star can be measured to calculate its distance. There are many such methods, and many of them involve basic astrophysics knowledge, so it is impossible to explain them all here.

Here is just one commonly used: astronomers often use the parallax method to measure the distance between stars.

Looking at an object from a different place will cause a change in the apparent position of the object, a phenomenon called parallax. When the Earth is on the Sun, they look at a star, and then six months later, when the Sun is on Earth, they look at the star again, and astronomers can measure the distance of the star against the background of a very distant star. The less a star moves, the farther away it becomes.

Pretty much all of them.

There are only a few planets in the sky that are visible to the naked eye, namely Mercury, Venus, Mars, Jupiter, Saturn, and Uranus.

Although the brightness of Mercury is not bad, the conditions for seeing him are really harsh, and it is generally impossible to see it without paying special attention to it (I have seen Mercury 3 times this year, early in the morning on January 8, and it was cold and I saw it twice in March, almost blocked by the city's buildings, and the two times add up to a total of 10 minutes).

The brightness of Uranus is barely visible to the naked eye, and it will be ignored if you don't specifically look for estimates (otherwise it won't be given to William.) Herschel to 1781 in the discovery was not).

The other four are bug-level, with quite amazing brightness, and they have steadily entered the ranks of bright stars, among which Venus and Jupiter are even more important, and they can even cause light pollution ...... in places with very good observation conditions

In short, with the naked eye, the stars seen in the sky are all stars except for the four above.

Strictly speaking, stars include the planets of the solar system (which reflect the sun's rays) and stars If you are not looking at the planets of the solar system, then they must be stars.

Because stars emit light, while planets don't, the stars that can be seen at night are basically stars.

We've all heard that when talking about sidereal distances, the numbers involved are incredibly large. That is, how do we know how far away a star really is? While there are many ways to calculate the distance between our planet and another star, there are three that are the most effective.

Through simple mathematical and logical reasoning, our astronomers give us a more vivid picture of the universe. Now sit back, grab a cup of tea, and get your brain ready for some incredible math.

Have you ever noticed that when you look out the window at a moving car, objects close to you fly by, while objects far away from you seem to move slowly in comparison? This is called the parallax effect. In the same way, as we revolve around the Sun, the positions of stars closer to Earth move steadily from one position to another, while stars farther from Earth seem to move less frequently.

Using this principle, astronomers can calculate the distance to nearby stars with considerable accuracy. First, astronomers record the star's position in the night sky. Six months later, the position of the same star was measured again.

First, you have to understand an effect called parallax. If you hold up a finger in front of your nose, about 20 centimeters away from your nose, and then alternately open and close one of your eyes, this finger will look like jumping from side to side. This is because each eye gives you a different visual effect, and there is a few centimeters between your two eyes.

If you know two extremely important dimensions: the distance between your eyes and the angle at which your fingers appear to be jumping, then trigonometry will help you figure out how far your fingers are from your eyes. The problem is that this method is suitable for observing close fingers, but not for objects farther away.

If you try to do this to a lamppost at the end of a distant road, you will find that you can't detect any movement at all – it's too small to observe.

So, to increase parallax, the eyes must be more apart. Astronomers use this effect to make one observation at a point in the Earth's orbit and then make a second observation before the Earth reaches half a circle around its orbit (which takes about six months). Knowing the distance between these two observations gives you the distance from the Earth to the Sun, and the same method can measure the distance between a star and the Earth hundreds of light-years away.

Changes in the brightness of stars are not directly visible to the naked eye, but are obtained by comparison with those stars that are stable (relatively speaking). Stars that are stable are called "comparators".

Visual observation of variable stars is to compare the difference in brightness between the "variable star to be measured" and the "comparison star". There are 3 methods of application: hierarchical method, interpolation method and joint method, and the commonly used method is Agrandel's hierarchical method.

If you want to distinguish these stars of varying light and darkness in the vast sea of stars, there are two methods: one is to divide the magnitude, and the other is to determine the luminosity.

In the 2nd century B.C., the Greek astronomer Hipparchus divided stars into six classes according to their brightness. The greater the brightness, the smaller the magnitude. What can be seen with the naked eye is a 6th magnitude star.

A star of the 1st magnitude is about 100 times brighter than a star of the 6th magnitude. Astronomers refer to the brightness and magnitude of a star observed on Earth as apparent brightness or apparent magnitude.

The apparent magnitude of a star is the brightness that people observe with the naked eye and telescopes, and it does not represent the true intensity of the star's luminescence. Because it is affected by the distance between the star and the observer, the farther the distance, the less apparent brightness will be. Therefore, to compare the true brightness of stars, they should be mentioned at the same distance as us.

Astronomers imagine that when a star is moved 10 parsecs away from Earth (i.e., 32 6 light-years), the apparent magnitude of the star is called "absolute magnitude". If we place the Sun 10 parsecs away from Earth, then we see the Sun only slightly brighter than a faint star of magnitude 5.

The true brightness of a star can also be expressed in terms of "luminosity". Like the Sun, the interior of the star undergoes a thermonuclear fusion reaction, which continuously transfers heat to the outer layers and finally shoots from the surface of the star into space. Astronomers refer to the amount of light energy released from the surface of a star every second as the luminosity of a star.

The luminosity of stars varies greatly, with the brightest stars being 1 million times stronger than the sun; The smallest star is only 1 1 100000 of the sun's luminosity. Interestingly, the Sun is exactly in the middle of the star's entire luminosity range. For this reason, astronomers often express the luminosity of a star in terms of solar luminosity.

They generally refer to stars that are about 100 times brighter than the Sun as giants, and the diameter of the giants is usually twenty or thirty times larger than the diameter of the Sun. Whereas, stars with less luminosity are called dwarfs and are also smaller in size. Giants and dwarfs are like giants and dwarfs in the stellar world, and the Sun is a yellow dwarf.

A supergiant star with a luminosity greater than a giant star is called a supergiant star, and Tianjin 4 is a supergiant star with a luminosity about 60,000 times stronger than the sun. The companion star of Sirius, the brightest star we can see with the naked eye (the brighter of the binary stars is called the main star, and the fainter one is called the companion star), is a white dwarf star with less than 1,1000 luminosity of the Sun.