Collection
zero Useful+1
zero

Right ascension

One of the coordinate values in the celestial equatorial coordinate system
Right ascension, yes astronomy Use in celestial sphere Equatorial coordinate system One of the coordinate values in the system, which is merged with Celestial equator Vertical, the other coordinate value is declination.
The angular distance similar to the longitude of the earth. Together with declination, it is used to determine the position of celestial bodies in the celestial sphere. It is calculated from the vernal equinox to the east along the celestial equator. Declination, similar to the latitude of the earth, refers to the distance from the celestial body to the northern and southern corners of the celestial equator [1]
Right ascension is a coordinate in the celestial equatorial coordinate system. It refers to the arc segment on the celestial equator between the right ascension circle passing through the vernal equinox and the right ascension circle passing through the celestial body, expressed in α. From the spring equinox, press Diurnal visual movement Measure in the opposite direction, from 0h to 24h [2]
Chinese name
Right ascension
Foreign name
right ascension
Abbreviations
RA
Symbol
α
Properties
Coordinate value
Corresponding coordinates
Declination
See publications
Astronomical Terms (Second Edition), Science Press
Time of publication
1998 [6]

Astronomical concept

Announce
edit
from Vernal equinox Go east along the celestial equator hour circle And Celestial equator The angle between the intersection points of is the right ascension of the object. Right ascension and Hour angle Different, the time angle is determined by celestial meridian The right ascension is measured from the vernal equinox to the east, and the two directions are opposite.
Right ascension finger Equatorial coordinate system Meridional coordinates of, through celestial sphere Previous Right ascension circle Vernal equinox Dichotomous circle The spherical angle of intersection. The celestial sphere is equivalent to the earth Meridian A line passing through the poles of the celestial sphere and perpendicular to the celestial equator. It is expressed in hours, minutes and seconds.
The algorithm of right ascension is special longitude (from - 180 degrees to+180 degrees), the right ascension is celestial equator 0 hours to 24 hours from west to east. Like time, each hour of right ascension can be divided into 60 minutes, and each minute can be subdivided into 60 seconds. The minutes and seconds of right ascension are not equal to the angles and minutes Angular second The conversion between them is 1 hour=15 minutes, 1 hour=15 seconds. The starting point of right ascension calculation is Vernal equinox The vernal equinox is the position of the sun at the annual vernal equinox (around March 21).

explain

Announce
edit
celestial sphere The right ascension of the upper part, its function and Geographical coordinates In longitude Same. Right ascension and longitude are vector degrees eastward or westward along the equator, and the zero point is also randomly selected on the equator. The zero point of longitude is Prime meridian The zero point of right ascension is Vernal equinox This is the point where the sun passes when it reaches the northern celestial sphere in late March Ascending intersection
The value of the right ascension is measured from the vernal equinox to the east in hours, minutes and seconds, but sometimes it is also measured in degrees. He and Sidereal time The relationship between. It is both a unit of time and a unit of angle. 1h=15 °, 1m=15 ', 1s=15 ". It is used in navigation Stellar hour angle (SHA), which is different from the right ascension in that the right ascension is measured from west to east, and the star hour angle is measured from east to west.
Right ascension can be used to measure the celestial sphere And can calculate the time when the celestial body reaches a certain point in the sky. For example, a celestial body located at 13h30m of right ascension is Meridional circle On the day when the right ascension is 20h, it will be 6.5h( Sidereal time )After passing the meridian circle.

history

Announce
edit
The concept of the Right ascension can be traced back to at least the second century BC, Hipachas He has known to use the right ascension to compile a catalog, but he and later astronomers used it Ecliptic coordinates , equatorial coordinates are used only in special cases.
Because of the invention of the telescope, astronomers can observe the celestial bodies in detail. In order to meet the needs of long-term observation, the telescope is installed in the Equatorial On the platform. Because as long as the equatorial instrument rotates the axis parallel to the earth's rotation axis, it can offset the earth's rotation and point fixedly at the selected celestial body. In short, Equatorial coordinate The system has been widely accepted by observers Spacer Can accurately point to the celestial bodies that already know the right ascension and declination. The first book uses equatorial coordinates fixed star Our catalog is John Fleming Steed The Historia Coelestis Britannica catalog.
Right ascension is the longitude coordinate of the equatorial coordinate system. It is the spherical angle intersected by the right ascension circle of a point on the celestial sphere and the half circle of the equinox. In 1857, Wei Lie Yali edited the "Six Harmonies Series" 11: "The British Boggson newly measured the asteroid, and its measurement is based on the London Observatory. At ordinary times, from noon, it is recorded here: at 9:54:13 on June 27, it measured the right ascension at 20:2:27:16, and the latitude at 16:20:53:7." The 1936 Science Pictorial Volume III, Issue 13: "Commerce is the heart of Scorpio, which is 180 degrees away from the Red Sutra of Betelgeuse." [3]

Related nouns

Announce
edit

Right ascension circle

The right ascension circle, also known as the time circle, is a large circle in the equatorial coordinate system. That is, the great circle passing through the celestial pole, which is the sub circle of the equatorial coordinate system. There are infinite right ascension circles, all perpendicular to the celestial equator [2]

Celestial coordinates

Celestial coordinates are also called "astronomical coordinates". A coordinate used to represent the position of a celestial body on the celestial sphere. Usually, latitude and longitude in celestial coordinates are Celestial coordinate system And the origin. It can be divided into four kinds: celestial horizon coordinates, celestial first equatorial coordinates, celestial second equatorial coordinates and celestial ecliptic coordinates.
The latitude in the celestial coordinates includes altitude (horizon latitude), declination (equatorial latitude) and ecliptic latitude (ecliptic latitude), which are equivalent to the geographical latitude in geographical coordinates; Longitude in celestial coordinates includes azimuth (or azimuth, that is, horizontal longitude), hour angle, right ascension (equatorial longitude) and Yellow meridian (longitude of the ecliptic) are equivalent to the geographical longitude in geographical coordinates.
Different celestial coordinates
Since the celestial sphere has different coordinate systems, the same celestial body has different celestial coordinates. As shown in the figure Different Celestial Coordinates, altitude and azimuth constitute the celestial horizon coordinate (a), declination and hour angle constitute the first equatorial coordinate (b), declination and right ascension constitute the second equatorial coordinate (c), and latitude and longitude constitute the celestial ecliptic coordinate (d). There are both differences and connections among various celestial coordinates. The ecliptic is the path of the annual movement of the sun, and the longitude and latitude of the yellow are particularly suitable for representing the movement of the sun, the planets and the moon of the solar system; The altitude and azimuth indicate the local position of the celestial body in the sky at that time; Declination and declination represent the fixed position of celestial bodies in the sky [4]
Celestial coordinates are commonly used in astronomy, including horizontal coordinates, ecliptic coordinates, equatorial coordinates, etc. In ancient China, the equatorial coordinates were most commonly used, and sometimes the horizontal coordinates and ecliptic coordinates were also used. They were unique things in ancient China, and played a unique role in observing stars and determining the position of celestial bodies [5]
(1) The establishment of the equatorial coordinates in ancient China can be traced back to the Warring States Period. It inherited the tradition of the location of the ancient 28 constellations. The two components of the coordinates are the degree of arrival and the degree of departure. The so-called degree of abode refers to the difference of right ascension between the distant star of the 28 constellations and a certain celestial body. For the 28 constellations, the amount equivalent to the degree of abode is the degree of distance. The difference of right ascension from a certain distant star to the next distant star is called the degree of distance of the night. The so-called de extreme is the angular distance from the measured celestial body to the North Pole, which is actually the residual angle of declination. The equatorial coordinate system was widely used in ancient Chinese astronomy, which is a typical example in the history of world astronomy.
(2) Ecliptic coordinates. The ecliptic is the orbit of the annual apparent motion of the sun on the celestial sphere. Based on the ecliptic, the position of celestial bodies is characterized by longitude and latitude of the yellow, that is, the ecliptic coordinate system. One of its components is also the degree of the ecliptic entrance, while the other component is sometimes used to extreme, and sometimes it is used to internal and external degrees of the ecliptic. The earliest explicit reference to the zodiac is the Shi's Star Sutra. Jia Kui of the Eastern Han Dynasty once quoted: "The Shi's Star Sutra said that the zodiac is the circle of the zodiac, where the early morning glory is the winter solstice point, and the zodiac is the landmark of the Shi's Star Sutra. The winter solstice point is 20 degrees, To the extreme is 115 degrees (25 is 115 degrees). At the end of the Han Dynasty, Liu Hong's "Ganxiang Calendar" again appeared the view of seeking the inner and outer degrees of the lunar ecliptic. It should be pointed out that the longitude difference of the ecliptic of the 28 constellations given in ancient China is not the difference of the ecliptic in astronomy, but the projection of the right ascension difference of the 28 constellations distant stars on the ecliptic. The so-called ecliptic distance of a certain night is the length of the ecliptic arc between the two right ascension circles of the star of this night and the star of next night. The so-called extragalactic and extragalactic degrees of the ecliptic refer to the amount in the latitudinal direction. Celestial objects to the north of the ecliptic are called inside the ecliptic, and objects to the south of the ecliptic are called outside the ecliptic. They are measured from the measured celestial bodies to the ecliptic along the right ascension circle of the celestial bodies.
(3) Horizontal coordinate. The coordinates established on the basis of the ground plane and the zenith (overhead direction) are called the horizon coordinates, and its two components are taken as the horizon azimuth and horizon height respectively. In ancient China, the original horizontal coordinate only had horizontal longitude, which was widely used to measure the azimuth of the sun's appearance and movement with sundials. In the Han Dynasty, the twelve geographical branches were often used to represent the orientation, such as Zi representing the north and Wu representing the south. Later, four dimensions, eight stems and twelve branches were used to represent the 24 directions. The four dimensions are: Gen represents the northeast, Xun represents the southeast, Kun represents the southwest, and Qian represents the northwest. Eight Gans are: A, B, C, D, Geng, Xin, Ren, Gui. The twelve branches are: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai. Together, they are the so-called twenty-four mountains, which represent twenty-four directions. These twenty-four mountains are only directional areas, not continuous measurements. Later armillaries were equipped with horizon rings, which were generally used in these 24 directions. The other component of the horizon coordinate is probably generated together with the theory of muddy sky. Tang Monk and his colleagues invented the complex moment diagram (instrument) to measure the height of the horizon. It was only in the Yuan Dynasty that Guo Shoujing invented the vertical movement instrument, which can measure both the height of the horizon and the longitude of the horizon [5]