China and Korea have a long history of star charts, dating from the prehistoric period. Historically, Korean astronomy has been deeply influenced by China over the last two thousand years, particularly on constellation system. Therefore, Chinese and Korean traditional star charts have many similarities in terms of shape of constellation, number of star, and so forth. Korean star charts, however, have lots of unique characteristics distinguishing from Chinese ones, such as, size of star and position of constellation. Overall knowledge of the Chinese star chart is required to study the Korean star chart. In this paper, I focus on introducing selected star charts in China and Korea. Although this review is very limited, I hope that this paper is helpful in research in the field of historical astronomy.
Gyupyo (圭表, Gnomon) consists of Gyu (圭, Measuring Scale) and Pyo (表, Column), and was one of the traditional astronomical instruments in East Asia. Daegyupyo (Large Gnomon) was manufactured in the Joseon dynasty around 1434 ~ 1435. To increase the measurement accuracy, it was equipped with a Hoengyang (橫梁, Cross-bar) and used a Youngbu (影符, Shadow-Definer) which was invented during the Yuan dynasty (1271 ~ 1368). The cross-bar was installed on the top of the column and this structure was called Eol (臬). In addition, three plumbs hanging from the cross-bar was employed to vertically built Eol on the measuring scale. This method was also used to not only check the vertical of Eol but also diagnose the horizontal of the cross-bar. Throughout this study, we found that a cross-bar in a gnomon has played three important roles; measurement of the shadow length made by the central part of the Sun, increase of the measurement precision using the shadow-definer, and diagnosis of the vertical of Eol and the horizontal of the cross-bar itself using the three plumbs. Hence, it can be evaluated that the employment of a cross-bar and a shadow-definer in a gnomon was a high technology in the contemporary times. In conclusion, we think that this study is helpful for understanding the Large Gnomon of the Joseon dynasty.
We have developed a data integration system for ground-based space weather facilities in Korea Astronomy and Space Science Institute (KASI). The data integration system is necessary to analyze and use ground-based space weather data efficiently, and consists of a server system and data monitoring systems. The server system consists of servers such as data acquisition server or web server, and storage. The data monitoring systems include data collecting and processing applications and data display monitors. With the data integration system we operate the Space Weather Monitoring Lab (SWML) where real-time space weather data are displayed and our ground-based observing facilities are monitored. We expect that this data integration system will be used for the highly efficient processing and analysis of the current and future space weather data at KASI.
An optical grism for education is fabricated and tested. It is composed of a transmission grating as dispersion element and a prism as diffraction angle compensation device. The transmission grating is Edmundoptics #49-584(spatial frequency 600 lines/mm, dimension 50 mm × 50 mm). The prism is the fused silica type with angles (41.3 , -48.7 , -90 ). The grism device is fabricated by bonding the transmission grating and the prism with an optical adhesive. The zig for assembling the grism, telescope and camera is composed of an aluminum tube, an aluminum disk ring and a T-ring camera adaptor. The fabricated optical grism spectrograph is tested in laboratory using Halogen lamp and Neon lamp with DSLR camera. And the grism assembled with reflector telescope is tested in a field using stellar light. The results show good agreements with design parameters. The wavelength coverage range of the grism is 250 nm at the un-deviated wavelength of 506 nm. The wavelength resolution is 0.11 nm/pixel.
This is the second paper on a systematic search for variable stars in Cyg OB3 region. In this paper we present the observational properties of 46 variable stars found in the region. Among them, 27 are eclipsing binaries and others are semi-long periodic or slow irregular variables. Only 5 are known variables and the rest are newly discovered ones. We have obtained the period and amplitude of 20 eclipsing binaries using the phase fitting method, and present the light curves of 46 variable stars.
A fiber-optic reference signal transmission system, which transmits the 1.4 GHz reference signal from H-maser to receiver cabin in radio telescopes, was adopted for compensating the phase changes due to temperature variation and antenna movement. At the first experiment, the remote signal’s phase changed more than 15 degrees at 1.4 GHz. We found unstable components in sub-system experiments and replaced them. The main cause of unstable phase stability was the unaligned polarization axis between Laser Diode and Mach-Zehnder Modulator (MZM). The improved system stability showed 1 × 10-16 allan standard deviation at 1,000 sec integration time with the antenna fixed. When the antenna moves in the azimuth axis, the 1.4 GHz remote signal showed the phase change smaller than 0.2 degrees.