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Observatory code was assigned by The International Astronomical Union (IAU) Minor Planet Center (MPC) for a permanent observatory that intended to do astrometric CCD-observing program of minor planet or comets in solar system. The purpose of acquiring an observatory code is to document specific details about a particular observation site and the types of instruments used within the observatory. In addition, many astronomical centers and stations worldwide will know there is an active observatory at the particular location and international cooperation program in astronomy observation is possible. The Langkawi National Observatory has initiated an observation program to monitor minor planet, specifically those Near Earth Objects (NEOs) that may bring potentially hazardous to the Earth. In order to fulfil the requirement that stated by MPC for undertaking astrometric CCD-observing program, an observatory code was required. The instruments and methods that applied to obtain the observatory code will be discussed. The Langkawi National Observatory is now coded as O43 and listed in the MPC system, the single worldwide location for receipt and distribution of positional measurements of minor planets, comets and outer irregular natural satellites of major planets.

Middle Age lunar crescent visibility criterion is criterion that was produced during 8th until 17th century. This includes al-Khawarizmi lunar crescent visibility criterion in 8th century until al-Lathiqi lunar crescent visibility criterion in 17th century. Numbers of review on mathematics and astronomy during the Middle Age, however the number of review that specifically written for Middle Age lunar crescent visibility criterion limited, with majority of review is written to study the historical of Middle Age science, astronomy, mathematics and geography as a whole, and not converge on lunar crescent visibility criterion. . Therefore, this article aimed to provide a review on Middle Age lunar crescent visibility criterion. The review is conducted using literature analysis, snowball literature search and specific inclusion and exclusion criteria. The review is performed based on 13 works on lunar crescent visibility criterion that pass the selection criteria. The review found out that most of the lunar crescent visibility criterion is based on al-Khawarizmi arc of separation and solar longitude, lunar crescent visibility criterion, with exception on Ibn Tariq, Ibn Qurra and Ibnu Yunus lunar crescent visibility criterion that adopt angular distance or elongation. The review suggest that a new outlook on Middle Age lunar crescent visibility criterion study can be done, by conducting an assessment on new data of moonsighting, and comparing with modern lunar crescent visibility criterion research.

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