Popular science composition 1500 words,

A good helper to identify stars-star map

Before you are familiar with the star map, you should know something about the magnitude. As we all know, the brightness of stars is different, some are brighter and some are darker. Astronomers use "magnitude" to represent the brightness of each star. The brightest star is 1, the barely visible star is 6, and there are 2, 3, 4 and 5 in the middle. For every magnitude difference, the brightness difference is 2.5 12 times, that is, the brightness of the star with 1 2 times that of the second-class star, the brightness of the second-class star is 2.5 12 times that of the third-class star, and so on. You will find that the brightness of a star like 1 is exactly 100 times that of a star like 6.

Astronomers found through accurate measurement that the magnitude of most stars is not an integer, and a few are brighter than 1. At this time, they are represented by numbers with decimal points and negative numbers. For example, the famous Vega is 0, Altair is 0.8, Sirius-1.4, arcturus -0. 1. Venus can reach -4.4 at its brightest, the full moon-12.5, the sun -26.7, and so on.

There are more than 6000 stars visible to the naked eye in the whole sky. However, when we look at the starry sky anywhere on the earth's surface at a certain moment, we can only see half of the sky, that is, we can only see about 3,000 stars above the horizon, and the other 3,000 stars are hidden below the horizon.

Just like drawing a map, drawing a map of the distribution of stars in the sky is called a star map. Star map is a necessary tool for us to identify stars. Open the star map and have a look. You will find that the patterns of bright stars in some constellations are very beautiful When you see the shapes of these constellations, you will think of many wonderful and magical stories, which not only increases your interest in reading star maps, but also provides convenience for understanding constellations and their main bright stars. But the myth is not true after all. In fact, the stars contained in each constellation are not members of a family and have nothing to do with each other. The patterns and shapes we see are just their projections on the celestial sphere. All stories, people, animals, instruments and utensils do not exist. Only two constellations are special. One is the Big Dipper in Ursa Major. They are the remains of the same cluster. The other is Orion, most of which are blue, because they are young high-temperature stars, all located in the same region on the same spiral arm of the Milky Way, from which new stars are constantly born. Orion is like a giant nursery for newborn stars. Of course, Orion is also mixed with many stars unrelated to these young stars. The most prominent is its main star, α-Betelgeuse, which should be the "mother" of this constellation, but in fact it is just in the same sight as these young stars in Orion, and Betelgeuse is much closer to us than them. Betelgeuse is a typical old star.

There are many kinds of star maps. At present, the most detailed star map used by astronomers has drawn 23 stars, which is also the limit magnitude that the world's largest telescope can see. The number of stars in the whole day is more than 500 million. There are several kinds of stars suitable for amateur observation, such as active star map, four-season star map and all-sky star map.

Active star map is a very simple and convenient star map. It consists of two disks: a chassis and an upper disk. The chassis can rotate around the center, and bright stars and constellations are painted on it. Coordinates are marked around the disk surface, and the month and date are marked. There are horizontal circles and notches in the four directions of east, west, north and south on the upper plate, and there are moments around the plate. When in use, rotate the chassis so that the date on the chassis is aligned with the observation time of the upper plate, and then the exposed part in the horizontal circular incision of the upper plate is the same as the starry sky that can be seen at that time. Hold the active star map above your head, so that the north-south direction of the star map is consistent with the north-south direction of the ground, and you can know the starry sky by comparing the star map.

The four-season starry sky map is to draw the starry sky of four seasons in spring, summer, autumn and winter on four pictures respectively. This is based on the vertical projection of celestial bodies from the zenith to the ground, so all four star maps are circular. The edge of the circle represents the corresponding geographical latitude and the four directions of east, west, north and south. The center of the circle is above the head, that is, the zenith. The stars in the four seasons star map are generally only drawn to level 3 or 4, and some larger star maps may be drawn to level 5. Because there is no dark star, the bright star is more prominent, which is more convenient for beginners to use.

All-sky map is a detailed map of all divisions of the whole starry sky. This kind of star map is very necessary for those astronomy enthusiasts who are already familiar with the starry sky and intend to further observe binary stars, variable stars, nebulae, clusters and galaxies, or prepare to look for new comets. This kind of star map is generally not available in the market. Interested readers can buy them at the Beijing Planetarium, which provides various star maps for astronomy enthusiasts all the year round.