In the Milky Way, there seems to be a center or approximate center position.
As it happens, the Milky Way is almost uniformly illuminated, which makes the assumption that the sun is at the center of the Milky Way somewhat reasonable. If the Milky Way is on the side of the center,
This orientation looks thicker and brighter than other orientations. Looking from the center of the Milky Way to the edge, you will find that there are fewer stars. On the other hand, walk towards it.
From the heart, we will face the far end of the Milky Way, where there seem to be many stars. However, no matter how reasonable it seems, the sun must be there.
The theory of the center or near the center of the galaxy is untenable. If it is true, not only all the stars in the Milky Way should be evenly distributed, but also the Milky Way.
Other orientations of stars should also be symmetrical, but this is not the case. After all, there are globular clusters that we discussed before. Most of them are located on one side of the sky,
And 1/3 is in Sagittarius.
Why is there such a unique asymmetry? 19 12 years, American astronomer Henrietta. Swan. When Levitt studied the Magellanic Cloud,
This answer has just begun to take shape. Two fuzzy patches, large magellanic cloud and small magellanic cloud, look like separate parts of the Milky Way. Only from the south
The hemisphere saw them, Ferdinand, the first European to see them. Named after Magellan, it crossed South America in 152 1 year.
At the southernmost tip of strait of magellan.
John. When Herschel studied them at the southernmost observatory in Africa 1834, he found that they were made up of many stars like Magellan in the Milky Way.
Clouds extend many light years in the sky, but because they are so far away from us, we can roughly think that they are the same distance from the earth (just like people)
Although the children are scattered all over Chicago, these people are about the same distance to Paris.
There are some variable stars in Cepheus in small magellanic cloud, which are roughly as far away as us. This kind of star is John. Gudrico found it at 1784. Xianwang constellation
A variable star is a variable star, and its characteristics are determined by two factors: mass and distance. And the brightness increases with the increase of star mass, follow me.
The distance between children is increasing. Therefore, very bright stars are either very large or very close to us. But to distinguish which hypothesis is correct, generally speaking.
It is out of the question. However, considering that all Cepheus variables in small magellanic cloud are roughly the same distance from the Earth, in this case, they can be ignored.
Distance. If we find that one star in small magellanic cloud is brighter than the other, then we should understand that we can come to the conclusion that the star we feel brighter must be two.
The bigger one, actually. Levitt found that in the small magellanic cloud, the brighter the Cepheus variable, the longer its change period and luminosity.
There is a consistent relationship with the cycle.
Then, if you know the distance of a particular Cepheus variable, you can measure its period. According to these conditions, you can determine its luminosity.
The photometric period curve discovered by Levitt is obtained. Then, you can study any other variables of Cepheus. According to its cycle, through Levitt
We can know its luminosity from the picture, and then on this basis, we can get how far the star with such brightness is in the sky. This "Cepheus variable star"
Standards can measure the distance between stars, but the distance is too far, which leads to measurement errors. However, we understand that even the nearest Cepheus changes due to parallax.
The star is too far away from us to determine its distance, so we don't have a distance map. We must build it first.
However, in 19 13, Hezipulu (the person who discovered the red giant star) managed to solve some distances of Cepheus variables that ignored differences through careful reasoning.
From, thus establishing the standard. 19 14 years, American astronomer Harold. Shapley applied this criterion to Cepheus in different globular clusters he designated.
Variable stars He gets the distance of each cluster, and then designs their patterns in their respective directions and distances. This provided him with all the information about globular clusters.
Three-dimensional model, he found that the model formed an approximate celestial sphere, and its center was thousands of light years away from Sagittarius.
Shapley thinks it is reasonable that globular clusters are located in the center of the Milky Way, so they seem to be far away from us. In fact, he overestimated it.
Today, we know that the sun is not located at or near the center of the Milky Way, but 3000 light-years away on one side.
In that case, why don't we think that the Milky Way is much brighter in Sagittarius than in the opposite direction? In fact, to some extent, the Milky Way.
Sagittarius is brighter and more complicated than other directions, but we can't see the center and edge of the galaxy. Dark nebulae scattered throughout the galaxy.
Covering most of the stars in that direction. In other words, when we look at the sky, we only see a relatively small part of the Milky Way, which constitutes the distance from the earth.
The nearest external area of the yang system-our neighbor. If we only consider this part of the Milky Way, we are located near its center, but far away from it.
The actual center is still far away.