Service Dept. (2016). "Leap Seconds". United States Naval Observatory. United States Naval Observatory. "Universal Time". "Universal Time". Oxford Dictionaries:
AstronomicalObservatory of Mallorca (esp. Observatorio Astronómico de Mallorca, OAM) on observatorio Mallorcassa, Espanjassa. Observatorio avattiin toukokuussa
Francesco Manca: Sormano AstronomicalObservatory: Table of Next Closest Approaches to the Earth by Asteroids AstronomicalObservatory of Brera. Viitattu 31