Calculation Position of The Moon and Sun During Observation Hilal 26 June 2025 at Bosscha Observatory Using The Astronomical Almanac 2025 Khaulatul Azwari(a*), Maulana Hendra Pratama(a), Alfadiyah Zilda Rosa(a)
a) Department of Atmospheric and Planetary Science, Institut Teknologi Sumatera, Indonesia
*khaulatul.122290006[at]student.itera.ac.id
Abstract
Calculating the positions of the Moon and Sun prior to observing the crescent moon is important in order to facilitate observation. One source of accurate data that can be used in these calculations is the Astronomical Almanac. The Astronomical Almanac is an annual astronomical publication containing ephemeris data on celestial bodies, such as the Moon and Sun. The Hilal, which determines the start of the Hijri month, heavily depends on its visibility, specifically when the young crescent moon appears shortly after conjunction. This calculation is performed using a hisab-based method utilizing ephemeris data from the Astronomical Almanac 2025. The process of performing these calculations involves interpolation and correction of the observers latitude and longitude relative to the Right Ascension (RA) and Declination data of the Moon and Sun, as well as converting the time of sunset based on the observation location. The results obtained from these calculations will be used to assess crescent visibility parameters, such as the altitude of the Moon and Sun, azimuth difference, and elongation angle relative to the Sun.
Keywords: Astronomical almanac- Calculation- Crescent Moon- Interpolation- Moon- Sun
