How to use the star map

Activity star map is a simple tool for teenagers, primary and secondary school students and astronomy enthusiasts to know the stars, and it is also a convenient teaching aid for teachers to guide students to know the stars. It is also a guide for professionals, field workers and PLA officers and soldiers to identify the stars and determine the direction at night. It consists of an upper plate and a lower plate. The upper plate is called a station, and there are five circles in the plate, which represent the horizon of the region with 250, 30, 35, 40 and 45 north latitude respectively, and can be selected all over the country. The lower disk is called the astrolabe, and it is marked with more than 800 stars of grade 5 or above and some famous nebulae and clusters.

In addition to identifying stars, this star map can also be used for the conversion of sidereal time and solar time; You can check the date of the 24 solar terms of the lunar calendar, the time and approximate location of sunrise every day. Its usage is as follows:

Cognitive constellation

On a clear night, turn the astrolabe. Make the date and time in the altimeter and the site consistent with the observation date and time, and then select the corresponding window in the upper plate according to the geographical latitude of the observation site. At this time, the constellation presented on the star map is the constellation above the observation site. Put the star map on the top of your head and align the position indicated on the star map with the actual position, then the constellation in the star map corresponds to the constellation of the actual starry sky, and the stars can be identified at this time. Instead, you can tell the direction according to the constellation.

Check the time and place of sunrise and sunset.

The position of the sun on different dates is marked on the ecliptic of the astrolabe. If you want to check the time and orientation of sunrise and sunset on a certain day, put the center point "O" of the sun on the horizon at the eastern edge of the astrolabe, and then find out the station time corresponding to the corresponding date from the edge of the astrolabe, which is the sunrise time. If the sun's center point "O" is placed on the western horizon, the sunset time can be found according to the above method, and their positions can be estimated. However, because this map is only an estimation, for the sake of simplicity, only the following amendments are made; That is, when there is no time to check the sunrise and the sun in February, you can add 10 minutes to the checked time. If 10 doesn't have time to check the sunrise and the sun, subtract 15 minutes from the checked time, and you can directly use the time found in the star map in other months without adding or subtracting.

Check the dates of the 24 solar terms in the lunar calendar (that is, the summer calendar)

The outer circle of the astrolabe is marked with characters of 24 solar terms, and there are arrows on the characters. The grid indicated by the arrow indicates the corresponding date of solar terms. However, due to the alternation of leap year and peace year in Gregorian calendar, the exact dates of some solar terms are advanced or delayed by one day in the years before and after leap year. The arrow indicates that the date of solar terms in the middle of the grid is basically unchanged, and the date of solar terms on the line has two years every four years, and the day after that has two years; The arrow next to the grid indicates that the year of solar terms is the day before or the day after every four years.

The transformation of time

When the solar time is converted into stars, the astrolabe is rotated to make the moon and day in the astrolabe coincide with the observation time in the station, and then the corresponding time (the right ascension of the star in time) in the astrolabe is found from the south point (12 time line) of the meridian in the station, and vice versa.

Time correction

This map is based on the longitude of east longitude 120'. For areas far away from east longitude 120', it is necessary to correct them in time. The correction values are longitude person c of the observation site and longitude person of the standard time. When observing stars at an observation site, Tc and T represent the difference between local time and standard time respectively.

Then TC-TN = in c-in n.

TC = TN ten(c-n)

In type P, n is east longitude 120, that is, n = 8H000S (h, m and s respectively represent hours, minutes and notes). Find the longitude of the observation site from C on the map, then read the standard time TN (afternoon plus 12) from the clock, and substitute the above formula to get the local time TC of the observation site. For Fujian, TC and TN are very close and do not need to be converted.

This star map is enough for the plan of the north pole center. The constellation image is realistic, which is convenient for beginners to identify the stars. This is the biggest advantage of this star map, but the constellations south of the equator are sparse, stretching along the latitude (especially the constellations below-45), and the constellations north of the equator are dense, which cannot be used as a comparison of constellation sizes.