1610 65438+1October 7th is an important day in the history of astronomy. What did Galileo discover from the telescope on this day?

If we scan the sky roughly with the naked eye, it seems that we have seen all the stars in the sky. There is no place where the stars look particularly dense, and there is no place where the stars look particularly sparse. From this, we can draw a conclusion that, for us, stars are evenly distributed in all directions. If the stars as a whole can form an aggregate of a certain shape, then the shape must be spherical. Obviously, all large celestial bodies are similar to spheres. Why can't the whole galaxy be regarded as a sphere?

Of course, there are only 6,000 stars that we can see with the naked eye, and most of them are quite close to us. What will we find if we use a telescope? The answer is that we see more stars, which seem to be evenly distributed in the sky-except the Milky Way. To the naked eye, the Milky Way is a weak band of light (now if we live in a city, it is difficult to see the Milky Way because the sky is artificially illuminated). It looks pale milky white. In fact, there is a fairy story about it: a long time ago, when Zeus' wife Hera was breastfeeding her baby, her milk flowed into the sky, forming this faint light band. The Greeks called it galaxias kyklos (silver ring), and the Romans called it via lactea (Galaxy), from which we got its English name.

But what is the real Milky Way? If we don't consider fairy tales, then we can first think of the ancient Greek philosopher democritus.

Around 440 BC, he proposed that the Milky Way actually consists of a large number of stars, which cannot be distinguished separately. But they gather together to give off a soft light. Although this view has not attracted people's attention, it is completely correct. 1609, Galileo aimed the first telescope at the sky and found that the Milky Way contains a large number of stars. This theory was confirmed.

What do you mean by "a huge number"? When people look at the night sky, their first impression is that there are countless stars, too many to count. But I mentioned that

After several times, the total number of stars visible to the naked eye is only about 6,000, and the number of stars visible through the telescope is much more. Does this mean that they are countless?

The stars in the direction of the Milky Way are very dense, while the stars in other directions are relatively rare, which means that we must abandon the stars that form spherical structures.

Overall concept. In that case, there should be as many stars in all directions as in the direction of the Milky Way, and the closer the stars are, the weaker they are.

The light flashes in the background (not as spectacular as it is now) and the whole sky will be lit up.

Then, we must assume that stars exist in large aspherical clusters and extend farther in the direction of the Milky Way than in other directions. In this case, the Milky Way galaxy shows that all the stars gather in the shape of a lens or hamburger. This lens-shaped cluster is called the Milky Way (Greek explanation comes from the Milky Way), and the name of the Milky Way has been preserved because of the dark light band around the sky we see.

The first person to suggest that stars exist in shadow galaxies is Thomas, a shadow astronomer. Wright. He put forward this suggestion in 1750, but his idea seemed so confusing and incomprehensible that few people paid attention to him at first. Of course, even if the Milky Way is lens-shaped, it can always extend in the long diameter direction. Although only a few stars can be seen outside the Milky Way, there are countless stars inside the Milky Way.

To illustrate the problem, William. Herschel counted the stars. It is naturally impossible to count all the stars in a certain period of time.

Herschel chose 683 small areas, evenly distributed in the sky, and then counted the stars seen through the telescope in each area. In this way, he got the number of stars that we now call "imaginary voting" in the sky. This is the first example of the application of statistics to astronomy.

Herschel believes that the number of stars in each region is related to its proximity to the Milky Way. In all directions, the number of stars increases with the approach to the Milky Way.

Steady growth. From the number of stars he counted, we can estimate the number of stars in the Milky Way and the possible size of the Milky Way. 1785, he announced the results, and proposed that the long diameter of the Milky Way is about 800 times the distance from the sun to Sirius, and the short diameter is 150 times this distance. Half a century later, the actual distance of Sirius was calculated, and Herschel concluded that the long diameter of the Milky Way was 8000 light years and the short diameter was 1500 light years. At the same time, he calculated that there are 8 billion stars in the Milky Way. Although this is a huge number, it is not uncountable.

In the past two centuries, astronomers have explored the Milky Way with much better instruments and techniques than Herschel. Now they know that the Milky Way is bigger than Herschel.

The ears are much bigger than expected. It extends at least 654.38 million+light-years in the long diameter direction and may have 200 billion stars. However, it can be said that we have confirmed that galaxies and stars are not numerous but computable, thanks to Herschel. In the clear night sky, there are more than 6000 stars that can be seen and counted. Some are bright, some are dark. Therefore, as early as more than 2000 years ago, people began to divide the stars seen by the naked eye into six grades according to their brightness, and called the unique brightness grade in astronomy magnitude. The very bright star is 65,438+0, and the naked eye is 6. Modern astronomy has continued this tradition, clearly stipulating that the brightness difference is about 2.5 times for every difference 1 magnitude. It is also stipulated that the brightness ratio 1 star is 0, and the bright one is represented by a negative number. For example, the magnitude of Sirius is-1.46.

Next, we will start with the identification of constellations, so as to know and study these stars!

Constellation, in the history of European astronomy, refers to several bright stars in an airspace and the surrounding dark stars, which are connected by imaginary dotted lines to form certain images, such as lions, bears, warriors and fairies. Attach charming fairy tales to become a vivid, easy to identify and find constellation.

There are 88 constellations all day. In each constellation, the stars are named by Greek letters according to their brightness, and the brightest one is called? (Read alpha in Chinese and call it in turn? (beta)，？ (gamma),? (Delta)？ (ε) ... until 24 letters are arranged and the stars have names. It is very convenient to identify the stars by taking the constellation where the stars are located as the surname and the arranged letters as the names. For example, Vega, which is familiar to China people, is the brightest constellation in Lyra according to modern astronomy? Star.

However, with the increase of the magnification of astronomical telescope, astronomers found that there are far more than 24 stars in a constellation, and it is more complicated to determine the numbering order by the old method, so we use the latitude and longitude of the celestial sphere to divide the starry sky area to define and determine the constellation.