Umbral oscillations are a type of fundamental phenomena occurring in sunspots. Accurate measurement of umbral oscillation period is important to the understanding of the structure and evolution of sunspots. A high-quality observation of the sunspot within the active region AR10593 was carried out by the spacecraft HINDOE in May 1, 2007 at the Ca II line. By using the Fast Furiour Transformation (FFT), we derive the oscillation period of the sunspot to be about 154s, which means the umbral oscillation in the Ca II line formation region is a typical 3min oscillation.

To open new opportunities on radio astronomical research with the recently constructed YNAO 40m radio telescope, we carried out test observations of extragalactic radio sources. Three compact radio sources (3C273, 3C295, and 0716+714) were observed with the ON/OFF mode. In such a mode the telescope was pointed first toward the source and then 2 degrees off the source. In each cycle there are 2 minutes on-source observation and 2 minutes off-source observation. The observational wavelength bands were alternated between the S and X bands but with short time intervals. We present here the S- and X-band flux-density curves of the three sources. There are unexpected drifts on various time scales in these curves. The sensitivity limits of the observations are about 1 Jy. Through the observation, we have identified problems of the telescope stability and environmental radio-frequency interference. By pointing the telescope to the Zenith without tracking, we found ≤1% per hour drifts in the flux-density curve, which are much less than the drifts observed in an ON/OFF mode for a source. In the S band, there is a strong interference signal at the frequency 2142MHz. This interference signal has several harmonics, so that it polluted our data severely. The frequency interference in the X band is weaker than in the S band. We finally propose measures to improve the telescope capacity. These include developing of a counter-interference system, using a radiometer for measuring the K factor to eliminate gain drifts of devices, and performing drift-scan observation without telescope tracking to avoid other unstable factors.

The FAST (Five hundred meter Aperture Spherical Radio Telescope) will be the largest radio telescope in the world. There are three outstanding technological innovations in the FAST project: the unique Karst depression as the site for antenna, the light-weight focus cabin driven by cables and servomechanisms, and the active main reflector. When we set the main reflector, the surface shape (including errors in manufacturing) of each of its panels has significant influence on the convergence of electromagnetic waves. It is necessary to measure the surface shape so that it can be set correctly. The FAST main reflector consists of 4600 triangular panels spliced together, each of which has a side length of 11 meters. The large sizes require certain fine technique for measuring surface shapes. In the photogrammetry a measured object is not physically contacted but measured through its image. The photogrammetry can have high efficiency when applied to wide-spread or multiple objects. Currently, the projects of world's largest radio telescopes, such as the GBT and ARECIBO reflectors all use the photogrammetry for surface measurement. After investigating and testing existing methods of surface measurement we propose a method of close-range digital photogrammetry. With this method, the surface shape of an eleven-meter panel of the FAST reflector can be measured in a few minutes. ur results show that the accuracy of the method in measuring a single panel is 2.30mm with a standard deviation of 5.00mm. The accuracy of the reflector panel surface was 3.0mm after adjustment. It is thus feasible to use the photogrammetry for measuring surfaces of single panels of the FAST reflector.

With the development of radio astronomy, the EMC (electromagnetic compatibility) problems of radio observing systems are becoming increasingly severe. Mastering cable wiring of such systems can benefit EMC project management and help improving system design. Based on the components and characteristics of electromagnetic compatibility of the Urumqi VLBI station, we analyze the electromagnetic compatibility of the systems under the adopted cable wiring. We subsequently propose shielding, filtering, and grounding methods to provide engineers valuable schemes to solve practical problems of electromagnetic compatibility. However, our work is only an initial stage, and more practical work is needed in the future according to our tests and simulations.

The VLBI terminal technology is developing rapidly over the world in recent years. Recording systems of the Mark5B type are installed in increasingly more stations, while the Mark5C type is under development and tests. In order to meet future requirement of high-speed recording, massive-data storage, and observations with DBBC, we need to upgrade the Mark5A to Mark5B or Mark5B+. Accordingly, a Mark4 formatter needs to be upgraded to a Mark5 sampler module. This paper describes the principle of relevant devices and the procedure of the upgrade of a Mark4 formatter.

To reduce the dependence on the high-precision time service provided by the GPS, it is desirable for our country to establish a low-cost and high-precision time service system of independent intellectual property rights. In this paper, we present a new method of satellite time service achieved through the broadcasting of a communication satellite and using a high-stability ground-based atomic clock as the time-frequency reference. We study the theory and measurement of multiple-satellite and single-satellite time services with the navigation constellations constituted by high-stability ground-based atomic clocks and communication satellites. We particularly analyzed factors affecting time accuracy in these two types of methods. Because of the high stability of the time-frequency source our proposed forwarding approach of satellite time service can have improved ranging accuracy. As long as the systematic error of time delay is precisely corrected, highly accurate time service can be achieved with our approach as well: Time accuracy with the coarse acquisition code can be within 20ns and that with the fine short code is about 10ns. In short our proposed system has the advantages of flexibility, convenience, and broad applications.

In order to precisely calibrate the time settings of astronomical facilities in the Antarctica, we introduce a method of building a high-precision NTP server, which can collect valid timestamps from the NMEA0183 data and keep them to be of high precision using PPS signals. The paper gives the circuit schedules of using the G591 GPS module and also the building steps of the NTP server in details. Three comparative tests show that the NTP server based on the LinrxPPS is precise, stable, and reliable.

In this paper we present a study of simulating turbulence-influenced phase screens. Effects of inner and outer scales of turbulences on phase screens in simulating with different Monte-Carlo methods are analyzed. Our result shows the effectiveness of the SH-FFT method under certain specific astronomical observational conditions. By using multiple-layer model of atmospheric turbulences (corresponding to multiple phase screens), we introduce a new method for simulating astronomical images of short and long exposures. Using the new method, we simulated images of a point source with and without the correction by an AO system.

Under the influence of atmospheric turbulence, a telescope with diameter larger than atmospheric coherence length cannot reach its diffraction limit. Especially, when the telescope aperture is about 10m or larger atmospheric turbulence will significantly distort the result image. In this case, an Adaptive Optics (AO) system can be used for alleviating the effect. Since an AO system is rather complex, it is necessary to simulate it before actually having it built. Such a simulation normally consists of several parts: the wavefront propagation to the telescope, wavefront reconstruction, wavefront control, and deformable-mirror control. For the first part, a phase screen simulation is traditionally used to provide a series of simulated turbulence layers. Most traditional methods are based on the singular decomposition of the correlation matrix derived from a structure function, their speeds are thus low and the required temporary memory is large. For a simulation of large telescope or of long time, it can be more convenient if the duration of this step is shortened. In this paper, the author adapts a method previously used in wavefront reconstruction, the Fractal Iterative Method with complexity of O(N), to substantially speed up the simulation.

The major function of the Survey Strategy System (SSS) of the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) is to generate observational plans and direct sky surveys. The management of an object catalog will thus be the initializing step of a survey. Astronomers will need to select targets from various database resources according to their research subjects and then input data entries of the objects into the catalog. Using object-oriented programming and the JDBC technology, we have designed and realized a general tool for database access and object data input. It has the capability of accessing databases, extracting data of objects, converting data formats, inputting object catalogs, and supporting processing of massive amount of data. With this tool astronomers can select target objects and manage survey catalogs rather conveniently.

The current astronomical data publishing techniques are mainly based on Web pages and REST-style Web services. But there are many deficiencies in these techniques, in particular automated tools are not conducive to machine recognition and service invocation. The WEB SERVICE is a mature distributed-computing model. It has many advantages such as the cross-platform linkage and loose coupling so that it can be used to improve flexibility and automation of astronomical research. In this paper, we investigate applications of the WEB SERVICE in the Virtual Observatory and current major publishing techniques of astronomical data. On the basis of the investigation, we analyze how to achieve WEB SERVICE applications that comply with the IVOA specifications. We design and implement a Cone-Search Service application supporting both the SOAP and REST styles for an astronomical data publishing project. Our WS-I test results show that the service design is successful.

Polarimetry is one of the four major types of astronomical measurements (spectroscopy, photometry, polarimetry, and imaging). A polarization analyzer is an effective tool in polarimetry. We have realized a closed-loop polarization-analyzer control system, which consists of a step motor and an absolute encoder. The step motor is controlled through the TCP/IP protocol, and the encoder is controlled through the RS485 serial communication. The system has a polarization-angle measurement error of 0.42°, a stepping angle of 22.5°, and a slew range of 0~360°. These sufficiently meet the requirements for polarimetry. A traditional polarization-analyzer control system is of open loop and contains a step motor and a Hall device. Through the Hall-effect switch the initial position of the polarizer can be determined, and then commands are sent to the step motor for designated angles, such as 45°, 90°, 135°, and 180°. It is easy to be operated to realize its basic function but it has large errors because of lost steps of the motor, the number of which is hardly known. In case when the system is restarted after unexpected power out, the current position of the motor cannot be specified and the entire system (including the step motor) has to be initiated again. We use an absolute encoder to replace the Hall device in our closed-loop polarization-analyzer control system. We can inquire the absolute encoder to retrieve the information about the current position of the polarizer. The systematic error can be controlled by the encoder also, and the positioning accuracy depends on the resolution power of the encoder. There is no need to worry about any power off for the system because the position is displayed in real time. Overall, our polarization-analyzer control system has very good positioning accuracy and robust performance. It is convenient for polarimetric applications.

The 1m solar telescope of the Yunan Observatory has a spectrograph as one of its main terminal instruments. The telescope has an altazimuth mounting structure and a Gregorian optical system. In the process of tracking the sun, the solar image on the slit plane of the spectrograph rotates around the main optical axis because of the kinetics of the mounting structure and mirrors. Such image-field rotation should be compensated for the spectrograph to work properly. We first give an in-depth study of the image-field rotation on the slit plane, and analyze the variations of rotation angle and acceleration of image-field rotation with the solar hour angle. We subsequently provide key parameters about position detection and driving motors of the counter-rotation system based on the specifications of image-field rotation and requirement on precision of counter rotation. We finally give a design of the servo control of counter rotation for the spectrograph.

The one-meter equatorial optical telescope at the Weihai Observatory of the Shandong University was installed in June 2007, and since then it has been in commission. The value of seeing is one of the most important parameters for ground-based astronomy and the full widths at half maximum (FWHM) of stellar images can be used to indicate the seeing condition. In order to estimate the seeing condition of the Weihai Observatory, we processed all the observational data of the observatory in 2008 and 2009 to derive the values of FWHM automatically by an IRAF batch-processing procedure. In general the values of FWHM of stellar images are contributed from instrumental defraction, tracking errors, defocus, dome seeing, and so on. They may be larger than the seeing values obtained by a differential image motion monitor (DIMM), but they reflect the overall image quality of observations.We study all seeing data in these two years and analyze the correlation between the meteorological data and the seeing data. The results show that the median value of seeings (FWHM) at the Weihai Observatory is 1.69 arcsec and the typical seeing (FWHM) ranges from 1.2 arcsec to 2.0 arcsec. The best observing seasons are spring and autumn, and the observational condition in winter is also good. Temperature is the dominant meteorological factor for the fluctuation of seeing, perhaps because the air temperature gradient from the inside to the outside of the telescope dome triggers troublesome turbulence eventually causing large fluctuation of seeing.

In 1280 A.D.in the Yuan dynasty (from 1279 A.D. to 1367 A.D.) the Chinese ancient calendar Shoushi Li (or Shou-shih li) was made by Guo Shoujing (or Kuo Shou-ching) and his colleagues. The calender has a high precision. It is the last calendar designed by ancient indigenous Chinese scientists. The Shoushi Li is thus one of the most famous calendars in the ancient China, and was recorded in the Lizhi (ancient calendar book of China) of the Yuanshi (annals of the Yuan dynasty). There are seven important calculation parts in the Shoushi Li, including solar positions, syzygies, corrections of solar motion and lunar motion, eclipses, and so on. The locations of the five planets are also in the list. Almost every part has a corresponding section in a modern astronomical ephemerides. The period of its usage (from 1281 A.D. to 1644 A.D.) is the longest among calendars in the ancient China. It was also a new calendar system at the time, in the sense that it dropped the traditional method of carrying out calculations from an epoch of the distant past. The essential constants of calculation were obtained from meticulous observations. Currently this calendar can still predict the solar eclipse to occur in May 21, 2012 and the local circumstance in Beijing. The error for the time of the middle of eclipse is 4min and the error of magnitude of the maximal eclipse is 0.04. This paper also provides the results from the Shoushi li for local circumstance and accuracy during the year 1990 to the year 2050 in Beijing. The standard deviation of the time errors is 103.04min and that of magnitides at the maximal eclipses is no less than 0.33. After investigating 186 solar eclipses from the year 1280 to the year 2050, the overall accuracy of the Shoushi Li can be deirved. Considering missed and erroneous records of solar eclipeses the standard deviations of the two aspects should not be better than 50.65min and 0.19, respectively. We have extended the calendar algorithms in steps by using a computer, and we find that the errors of the Shoushi Li increases with time after issueing. This calendar has not been in use for 450 years, but in some cases it is still of high accuracy, and the solar eclipse in 2012 is an example.