Report of visiting the Chinese Astronomical Centers
Debi Prasad C.
Udaipur Solar Observatory
Physical Research Laboratory
11, Vidya Marg, Udaipur, 313 001, India
(The visit to Chinese Astronomical Centers was supported jointly by The Third World Academy of Sciences and Chinese Science Academy)
The quest for knowledge about the heavenly bodies, in as accurately as possible, among the Chinese can be traced back to the early down of the civilization. The record of the novae observations can be found as early as 14th century BC. The solar and lunar eclipse observations were very carefully made in 13th century BC in the Yin Dynasty. The observation of a large sunspot is described as "A bird setting in the Sun" in a book "Huai Nazi", "Han Shu" written in 28 BC. The book "Spring and Autumn" written in 613 BC records one of the earliest sightings of Comet Halley as "A star was shining near the Dipper in July" in Lu Wengong 14th Year. The accurate record of Crab Super Novae in 1054 AD has really proved very important in the modern astronomy to understand this object. The attempts to stretch the imagination for understanding the cosmic structure started as early as 12th century BC. The individuals who contributed in instrumentation in Chinese early astronomy are Zhang Heng, who was the director of astronomy bureau in the eastern Han Dynasty, Shen Kuo, who made the armilary sphere during "Song Dynasty" and Shoyjing, who made Abridged Armilla in Qing Dynasty.
The Ancient Beijing Observatory was built in the 7th year of the Zhengtong reign (1442 AD) of the Ming Dynasty. The observatory has a impressive building called Purple Hall built during Zhengton reign (~ 1437-1436 AD) of the Ming Dynasty. Recently, the hall was renovated and decorated. The platform of this observatory is 14 meters high with 8 large astronomical instruments made in the Qing Dynasty. These instruments display an impressive combination of scientific precision and artistic elegance. They are influenced by the post renaissance European astronomical achievements. We give a brief description of the instruments. Figure 1 gives the display of the Chinese ancient astronomical instruments.
Instruments made in Ming Dynasty
1. The Armillary Sphere: It was constructed in 1439 AD, 4th year of Zhengton to determine the coordinate of celestial bodies.
2. The Abridged Armilla: This instrument is similar to the Armillary Sphere in construction, operation and utility and made in the same year.
3. The Gnomon: This instrument was made in 1437-1442 AD, 7th year of Zhengton, to determine the length of a tropical year and 24 solar terms.
Instruments made in Qing Dynasty:
1. The Celestial Globe: Made in 1673 AD, the instrument was designed for measuring the time and azimuth of the rising and setting of celestial bodies, as well as measuring altitude and azimuths of celestial bodies at any time.
2. The Equatorial Armilla: Made in 1673 AD, it was meant primarily for measuring true solar time as well as right ascension difference and declination of celestial bodies.
3. The Ecliptic Armilla: Made in 1673, was meant to measure the ecliptic longitude difference and latitudes of celestial bodies as well as the 24 solar terms.
4. The Sextant: Made in 1673 AD, it was used to measure the angular distance less than 6o between any two stars as well as the angular diameter of the sun and the moon.
5. The Altazimuth: Made in 1673, meant to measure the azimuths of celestial bodies.
6. The Quadrant: Made in 1673, used to measure the altitudes and zenith distance of celestial bodies.
7. The Azimuth Theodolite: Made in 1715, was designed to measure the azimuths and altitudes of celestial bodies.
8. The New Armilla: Made 1744 AD, designed to measure the true solar time as well as the right ascension difference and declination of celestial bodies.
Nanjing Astronomical Instruments Factory:
Nanjing Astronomical Instruments Factory (NAIF), founded in 1958, is a special establishment of Chinese Academy of Sciences. It has three research divisions (a) Optics, (b) Construction and (c) Electronics control, in which about 530 staff members including over 200 scientists and engineers work. The main facilities are,
1. 2.5 m optical polishing machine,
2. 1.5 m optical polishing machine,
3. 1.0 m vacuum aluminizing tank,
4. 2.5 m and 8m vertical lathes,
5. 250 large floor type boring machines.
It has good facility to measure and test the large size aspherical mirrors, electro-optic modulators and birefringent filters. The experimental arrangement to test the KD*P modulators is given in figure 2.
The test facility of solar instruments include a 40cm celostat and a high resolution grating spectrograph. The spectrograph has the following characterstics.
Imaging Mirror: 12m, 30cm
Collimator f = 6 m
Grating: 600 groves mm-1, 100100 mm
Camera f = 7 m
Blazed in 5500 A, 2nd order
Standard = 0.02 mm
I was very much interested in the "experiment system of thin mirror active optics project" in which Dr. Xiangqun Cui was working. In this system, the experiment mirror has 500 mm apparature, 510 mm outer diameter and 6 mm thickness. There are 58 actuators and three fixed points in it. These actuators are arranges on five circles. Their radii are 0, 56.7, 113.3, 170 and 226.7 mm. Figure 3 shows the distribution of actuators. A Shack-Hartmann test apparatus is used for the measurement of wavefront aberration. All image points formed by it appear theoretical diffraction pattern. A CCD TV camera is used for sensing. A 486-class computer is used for calculating and controlling. From signal collected by CCD the wavefront aberration then the force f are calculated. All the step moters rotate according to the f and controlled by the computer. When a circle is completed, the new wavefront aberration is measured and corrected again if needed. Figure 4 gives the schematic out line of the experimental scheme. The wavefront aberration is fitted with Zernik Polynomial to get the residuals. The figures 4, 5 and 6 show the image after various stages of corrections.
Purple Mountain Observatory:
The Purple mountain observatory, Academica Sinica, situated at the third peak of the Purple Mountain towards the east of Nanjing was established in Nanjing in February, 1928 and the observatory was completed on september 1, 1934. It was renamed as Purple Mountain Observatory, Academica Sinica on May20, 1950 after founding of the People's Republic of China. It has sub-observing stations Qingdao observatory, Qinghi Observing Station, Qinghi Observing station for radio astronomy and Ganyu Solar observing station. The observatory is engaged in the research of astrophysics, celestial mechanics, radio astronomy, space astronomy and practical astronomy. It also develops the detectors for astronomical satellites and milimeter wave radio telescope. I have visited to see their solar telescopes in detail. Its spectrograph system is similar to the Nanjing University Solar towar, which will be described later. At this observatory, in a cave made to hide the astronomers during the 2nd world war bombing, the mirror polishing is done. The cave has exceptionally good temperature stability ~ 1 variation in the year. They produce flates of /10-20 quality.
Nanjing University Solar Towar
Nanjing University Solar Towar was shown to us by Dr. Huang You-ran. It has a celeostat consisting of 60cm mirror. Imaging lens is 40 cm. It gives 10' good field of view. The spectrograph as a dispersion of 1A/mm and resolution of R= 4 10. The floore and walls of the spectrograph room is wooden with black coating. The wooden floore and wall reduces humidity and dust.