pysky: An Application for the Planning of Multi-Target Astronomical Observations

To automate the process of planning and curating multi-target observation sessions, pysky application builds on the astroplan Python package to identify visible objects during an observation window and produce relevant information about those objects in visual and graphical form. The package calculates object visibility based on a provided time window and observing location as well as maximum airmass and limiting magnitude requested by the user. The pysky application images of the target objects with identifying and astrometric data to provide context for the images. In addition, pysky creates polar plots of each object’s horizontal coordinates, and the images and plots are designed to be shown side-by-side. The package also generates an HTML table of the selected target objects with their related data to relay the entire target list as one. The pysky application draws on a variety of Python packages to collect and process data from databases such as JPL Horizons and SIMBAD. Results for a test event were verified by hand using database web interfaces. The pysky application provides a platform for further integration of automated observation planning with websites and apps to enhance multi-target observation sessions.

Gnomon shadow lengths recorded in the Zhoubi Suanjing:the earliest meridian observations in China?

The Zhoubi Suanjing, one of the most important ancient Chinese books on mathematical astronomy, was compiled about 100 BC in the Western Han dynasty （BC 206 - AD 23）. We study the gnomon shadow lengths for the 24 solar terms as recorded in the book. Special attention is paid to the so-called law of ‘cun qian li’, which says the shadow length of a gnomon of 8 chi （about 1.96 m） high will increase （or decrease） 1 cun （1/10chi） for every 10001i （roughly 400kin） the gnomon moves northward （or south- ward）. From these data, one can derive the time and location of the observations. The resuits, however, do not fit historical facts. We suggest that compilers of the Zhoubi Suanjing must have modified the original data according to the law of ‘cun qian li’. Through reversing the situation, we recovered the original data, our analysis of which reveals the best possible observation time as 564 BC and the location of observation as 35.78° N latitude. We conclude that this must be the earliest records of solar meridian observations in China. In the meantime, we give the errors of solar altitudes for the 24 solar terms. The average deviation is 5.22°, and the mean absolute deviation is 5.52°, signifying the accuracy of astronomical calculations from that time.