Digital zenith telescope prototype of China

Classical optical astronomy measures the direction of the local plumb line on the stellar background,and is influenced by variations of the earth gravity field.Therefore,classical optical astrometry can be used to measure and study variations of plumb line.This endows classical optical astrometric technologies special significance for the interdisciplinary researches of astronomy and geoscience,and makes them irreplaceable by technologies like very long baseline interferometry,satellite laser ranging.However,classical astrometric instruments have a major drawback of low efficiency,such as the low automaticity,more operating observers,and even operative error which makes it very difficult to reduce the random observation error in some visual instruments.To overcome this drawback,we have successfully developed the digital zenith telescope prototype(DZT-1)with the aperture of200 mm,using charge coupled device and other advanced technologies and new equipments.As proved by test observations,DZT-1 can observe thousands of stars over one night,which significantly reduces the random observation error and increases the observation accuracy.In addition,DZT-1 has a high degree of automation,even allowing unattended observation by remote control.Besides,DZT-1 has a small-size and is easy to move,making it convenient for mobile measurement of the deflection of the vertical.In summary,DZT can be widely used in the geoscience and astronomy fields.

Image and data processing of digital zenith telescope(DZT-1) of China

The first digital zenith telescope prototype(DZT-1)of China was successfully developed by National Astronomical Observatories,Chinese Academy of Sciences and Shandong University of Science and Technology at the end of 2011.Compared with classical astrometric telescopes,DZT-1 has features of small size,high automation,and high accuracy.It can be used to do classical astrometric observations as well as measurement of plumb line variation and deflection of the vertical.So DZT-1 plays a significant role in astronomy and geoscience.Although the measurement principle and method of DZT-1 are somewhat similar to classical photographic zenith tube,there are still many differences.The present paper introduces the principle,method,and procedure for processing DZT-1 star image and data,as well as the application software for astronomical latitude and longitude calculation using DZT-1 observations.The test observations and the observation results are also presented.According to the test observation results,the standard deviation of single observation is about 0.200–0.300,and 0.0700–0.0800in term of a group observations.In conclusion,the data processing software fulfills DZT-1’s demand for data processing,guaranteeing the automation and high accuracy for DZT-1.

Revisit of short-term periodicities in solar mean magnetic field

Short-term variations of the solar mean magnetic field(SMMF) were investigated through re-analyzing the data from the Wilcox Solar Observatory during the last four solar activity cycles using continuous wavelet transforms.We demonstrated the time-variable characters of short-term periods of SMMF. Our results indicate that the SMMF has main periods of about 27 and 13.5 days not only in the minimum and maximum years of each activity cycle, but also in the increase and decrease of the solar cycle. The result is partly different from the conclusion that the SMMF has dominant period of about 27 days during the solar maxima and about 13.5 days during the solar minimum years(Ye et al. in Solar Phys 279:411–418, 2012). The entire time span of SMMF was investigated and discussed further.