What Is Solar Radius?
The radius of the sun is about 696,300 kilometers. When we look at the sun at the average distance between the sun and the earth, the radius of the sun is about 960 arc seconds, which is converted into line scale 1 arcsec (arcsec) = 725.3 kilometers (Km). The radius of the sun is not static, the sun itself has a process of contraction and expansion, so we generally refer to the radius of the sun as an average.
- The radius of the sun is about 696,300 kilometers. When we look at the sun at the average distance between the sun and the earth, the radius of the sun is about 960 arc seconds, which is converted into line scale 1 arcsec (arcsec) = 725.3 kilometers (Km). The radius of the sun is not static, the sun itself has a process of contraction and expansion, so we generally refer to the radius of the sun as an average.
- The sun was formed by the gravitational collapse of the primitive nebula. After the formation of the sun, it entered the main sequence star stage. Figure
- Meridian measurement
- Solar eclipse and Mercury transit;
- Telescope drift scanning technology;
- Contour method
- Satellite angular distance measurement.
- Due to geometric reasons, the influence of the optical balance of the moon on the moment of contact is much lower in the polar region of the moon than in other parts of the moon;
- In recent decades, the long-term observation of lunar occultation has greatly improved the correction of the topography of the lunar polar region.
- China is the first country in the world to measure the diameter of the sun. The method of measuring the diameter of the sun in "Zhou Huan Jing Jing" is: "Instantly take an inch of bamboo empty diameter. Eight feet long. Capture the shadow and look at it. The sky is covered by the sky. The sun should be the hole. From this view rate. Eighty inches. And one inch in diameter. Therefore, the sentence is the first. Take as the stock. From to the next 60,000 miles. And have no shadow. From above to the day. Then 80,000 li. At the rate of 80. The mile is one mile. The 100,000 mile is 1,250 miles. Therefore, the sundial path is 1,250 miles. " This passage means: take an eight-foot-long hollow bamboo pole with an inner diameter of one inch, and use this bamboo pole to point to the sun. When the sun crosses the meridian, measure the length of the pole shadow, at this time the round surface of the sun is just filled with the bamboo tube. When the length of the shadow is six feet, the ratio of the inner diameter of the bamboo tube to the length of the bamboo pole is one inch and eight feet, so the diameter of the sun is considered to be one eighth of the distance between the sun and the earth. This value and the diameter of the sun are one hundred and eighth of the average distance between the sun and the earth, and they are already relatively close. Zhang Heng described the angular diameter of the sun and moon in "Lingxian" as "hung like a bright moon. It is much larger than the sun and the moon. Its diameter is one-seventh of the week of the week." Converted to the current 360-degree system, which is 29'.21 '', which is only 2% less than the average angular diameter of the day and month measured by modern astronomy. '. Under the scientific and technological level and observation conditions at that time, this value was quite accurate [1] .
- French astronomer Picard measured the solar radius more accurately during the Monde minima. In recognition of his contribution to the study of solar radius, a satellite measuring the diameter of the sun launched by France in 2010 was named after it. The system's solar radius measurement began in the 19th century. In 1891, Auwers measured the solar radius to be 959.63 ", which was later published as the standard solar radius value. The measurement of the solar radius is mainly based on geometric principles. Common measurement methods are:
Solar Radius Meridian Measurement
- By recording the time the sun passed through the meridian circle and measuring the angle from the zenith to the upper and lower edges of the sun, this was an early work by the Royal Greenwich Observatory to measure the radius of the sun. This work continued from 1836 to 1953. Before 1851, the time of the sun passing through the meridian circle was recorded by listening to the sound of a pendulum. After 1854, this method of "eyes and ears" observation was replaced by the chronograph method, which can automatically record the time the sun passes through the meridian circle; the introduction of this method also caused the data to be discontinuous. In 1891 and 1906, the objective of the telescope was polished twice, which may affect the observation of the radius of the sun. The "impersonal micrometer" was installed in the telescope in 1915. This device would affect the measurement of the horizontal solar radius. Due to the human error caused by the measurement of different observers, the measured values will also be affected. Between 1861 and 1883, there were 9 observers; the average error range of the vertical diameter they observed reached 4.8, and the error range of the horizontal diameter reached 2.2 '. '. From 1915 to 1949, there were a total of 7 observers. The measurement results of 5 of them did not have a clear trend of change, and the results of 2 of them had relatively large and unstable personal errors. Therefore, the average value of the measurements of 7 people gradually decreased. Gives a false trend of decreasing solar radius. In addition, the method is limited by weather and observation conditions, such as "cloud occlusion", "instability", "undefined definition", "bad image", "extremely poor definition" and other factors. Therefore, meridian measurements are not suitable for studying possible changes in the solar radius.
Solar radius solar eclipse and planet transit
- The principle of measuring the radius of the sun is similar to the solar eclipse and the planetary transit phenomenon, and both use the principle of the orbital motion of the moon, the earth, and the planets to measure. A solar eclipse is when the moon moves between the sun and the earth. When the three are in the same straight line, the moon blocks the sun's light on the earth, and the shadow behind the moon just falls on the earth. It is assumed that both the sun and the moon are ideal spheres. Since their distances are known, by accurately measuring the four contact moments, the radius of the sun can be calculated. The relative distance between the sun and the edge of the moon moves at a rate of 0.5 per second. If the measurement accuracy at the moment of contact can reach the order of tenths of a second, the measurement accuracy of the solar radius will be higher than 0.1 . The solar eclipse is used to measure the radius of the sun. The most commonly used event is the Bailizhu event. During the solar eclipse, when the moon eclipsed the solar sphere, due to the unevenness of the lunar surface, daylight can still be emitted through the recess to form bright pearl-like light spots. Observe the name. By measuring the time when Bailey beads appear and disappear, the change in the radius of the sun can be estimated, and the accuracy can reach 0.01. The line length of 0.1 on the moon is about 190m, but on the moon, the maximum deviation between the true edge and the average edge can reach ± 2, which is much greater than 190m. Therefore, to measure the radius of the sun, it is necessary to know the topography of the moon's edge accurately. The accuracy is higher than normal, which is difficult to achieve. However, measurements taken near the limits of the alimentary zone can greatly improve the situation because:
- Mercury transits (and Venus transits) occur similarly to eclipses. When Mercury or Venus runs between the sun and the Earth, when the three are exactly in a straight line, Mercury or Venus blocks part of the sun's surface. On Earth, you can observe a small dark spot on the sun moving slowly. This phenomenon is called Mercury or Venus transit. The surveyor can calculate the solar radius by recording the time when Mercury or Venus passes through the circular surface of the sun, and using parameters such as the distance between Sun and Earth and the distance between Mercury and Earth. Mercury transits occur about 13 times every 100 years, and the diameter of the sun measured by the Mercury transit has been over 300 years old. Morrison and Ward summarized 30 Mercury transits in the past 250 years in 1975. In the past, the history of measuring the diameter of the sun was mainly measured by the transit phenomenon of Mercury. The Mercury transit is a highly accurate method for measuring the radius of the sun. According to the orbits of the Earth and Mercury, the transit of Mercury occurs in May or November and has the longest duration in May (crossing the circular surface of the sun). It was 8 hours, and in November it was 6 hours. If the time recorded when Mercury just touched the edge of the sun can be accurate to 1 s, then the resolution of the obtained solar radius can reach 0.1 . However, because it is difficult for observers to distinguish Mercury's first contact with the edge of the sun, the standard deviation of each observation can reach 0.5 ~ 1.
- The conclusion of the research on the measurement of the solar radius by Mercury transit has not been unified. Shapiro believes that the solar radius has shrunk. Shapiro et al. Believe that the radius of the sun does not change by more than 0.1 '' in 100 years, and the change in radius has a period of 80 years. Sveshnikov found that the solar radius changes with 80-year and 11-year cycles. Emilio et al. Measured the radius of the sun on Mercury transits on May 7, 2003 and November 8, 2006. This is the first time in history that Mercury transits measured the radius of the sun from high-precision measurements from space. Their measurements are It is 960.12 ± 0.09. The history of the measurement of the solar radius by the transit of Mercury and Venus is relatively long, but due to the limitation of observation time, frequent measurements cannot be performed, and the data obtained are sporadic.
Solar Radius Telescope Drift Scanning Technology
- Telescope drift scanning technology, also known as time-delay integration readout technology. Using the principle of step-by-step charge transfer of CCD, the speed of parallel transfer of the charge in the column direction (realized by the vertical clock) and the speed of serial read data in the row direction (implemented by the horizontal clock) are achieved through the sequential circuit. The magnitude of the drift speed is matched; the purpose of charge tracking is achieved while the charge is being accumulated, because there is no relative movement between the target image on the CCD photosensitive surface and the CCD electronic image, so that the image formed on the CCD photosensitive surface follows The targets drift together to obtain a circular star image with good moving celestial bodies. Wittman et al. Used this technique to measure the radius of the sun. Wittman et al. Measured the radius of the sun 1122 times from July to October 1990 (including 472 times at Izana , 650 measurements in Locarno), the average solar radius R = 960.56 "± 0.03 was measured. Their research shows that the amplitude of the solar radius change will not exceed 0.3".
Solar radius contour method
- Laclare of the French Observatory has measured the radius of the sun with a contour meter since 1976. Xu Jiayan et al. Summarized its measurement principle: observe the moments when the upper and lower edges of the sun pass through these high circles on the same contour circle. In order to improve the observation accuracy, the upper and lower edges before and after each contour of the sun should be recorded multiple times, and these records should be counted to the time when their edges are tangent to the contour, and then their average value. Although the apparent circle of the sun is large, since the moments when the upper and lower edges of the sun pass through the same contour circle, the correction of atmospheric refraction is performed on the same zenith distance, so the influence of the atmospheric refraction coefficient error is relatively Small and negligible. On this basis, Xu Jiayan et al. Proposed two schemes (single-image scheme and dual-image scheme) for measuring the radius of the sun using a photoelectric altimeter, and carried out simulation calculations. The results show that both schemes are better than 0.1. France The solar radius data measured by the Calern Observatory is the longest in the history of measuring solar radius. There is a relatively continuous set of data years ( 1976-2006), which is widely used for periodic analysis of solar radius (Golbasi et al. The results of measuring the radius of the sun by the drift scanning method and the contour method are summarized.
Solar radius satellite angular distance measurement
- At present, there are mainly two satellites measuring the solar radius. They are SOHO / MDI and Picard satellites. The advantage of satellite observation is that it avoids the effects of atmospheric disturbances and seasonal factors, so the observations are more accurate and continuous. MDI uses the theoretical model of the sun to observe the solar mode oscillation to obtain the radius of the solar earthquake. The measured data has the characteristics of high stability and low noise. The solar earthquake radius measured by MDI corresponds to a height range of 5000 ~ 10000km below the photosphere layer, which is different from the solar radius measured from the center of the solar sphere to the surface of the photosphere layer. Compare directly. Schou analyzed the f-mode frequency of MDI observations and pointed out that the solar heliospheric radius observed with MDI is R = (695.68 ± 0.03) Mm, which is greater than the standard value of solar radius R = (695.99 ± .0.07) Mm (million meters) It is nearly 300km smaller. Emilio et al. Compared the number of sunspots smoothed by Fourier, the solar radius observed by the ground telescope of the CERGA Observatory and the solar radius observed by SOHO / MDI, and found that the amplitude of the increased solar radius observed by the MDI is much smaller than that of the CERGA Observatory ground telescope. Observed solar radius. Sofia et al. Point out that the change of the radius of the photosphere is much larger than the change of the radius of the sun below the photosphere. Kuhn et al. Studied MDI solar radius data and concluded that the annual variation of the solar radius does not exceed 15 mas / a. Similarly, the study by Bush et al. Showed that the variation of the diurnal radius does not exceed 1.2 mas / a. Emilio et al. Used MDI to measure the solar radius of 959.28 "+/- 0.15"; this value is slightly smaller than the value measured by the ground telescope, but it is in good agreement with the value measured by Schou. The Picard satellite was launched on June 15, 2010. Its main goal is to measure the solar irradiance, solar radius, and solar edge contour more accurately, and to study the internal conditions of the sun through the method of solar earthquakes. The solar diameter and surface imager in the Picard satellite measures the solar diameter every minute with an accuracy of a few thousandths of an angular second. We also expect the data measured by the Picard satellite to accurately characterize changes in the solar radius.