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Historia obserwacji zakryć

Historia obserwacji zjawisk zakryciowych jest opisana na stronach 12 rozdziału poradnika IOTA: http://www.poyntsource.com/IOTAmanual/IOTA_Observers_Manual_all_pages.pdf


Program Occult zawiera bazy danych obserwacyjnych od roku

There were some naked-eye occultations observed before the 1600’s; some of them are in Newcombe’s papers. Besides some from antiquity, Arab astronomers between about 500 and 1200 AD observed several. While ILOC was collecting observations, on the cover of their annual publications, they included a representation of an occultation of Aldebaran that had been observed in the 7th century AD in Japan. The observations have been used, along with observations of total and deep annular solar eclipses, to determine long-term variations in the rotation of the Earth (called “delta-T” – see https://en.wikipedia.org/wiki/%CE%94T), by workers including Leslie Morrison and F. R. Stephenson. In May 357 BC, Aristotle observed a lunar occultation of Mars, proving that the planet was more distant than the Moon; see https://journals.sagepub.com/doi/abs/10.1177/002182860003100405?journalCode=jhaa . Some even earlier occultations are noted in records from ancient Egypt and Babylon.

Just a little more on this issue, for those interested in history.

APAE Vol IX, Part 1 is available on-line – for a page-by-page view. The Preface, and Concluding remarks, are most interesting reading for anyone interested in the history of astronomy and the moon’s motion.

The Preface is at




and the concluding remarks are at:




1. Simon Newcombe (US Naval Observatory) collected old observations of lunar occultations. They are published in two locations:
  Washington Observations for 1875, Appendix II (observations before 1750) – available from GoogleBooks
  APAE Vol IX, Part 1
Newcombe was trying to derive a reliable ephemeris of the moon – which was a huge problem back then.
Part of the problem with old timings was time itself. Accurate clocks were not developed until the 1800’s. The first timed observations (1600’s) have residuals in the many 100’s of arcsec (you can view these in Occult – Lunar Observations./ View/analyse… and select the menu option to read a file – and read the 1600-1949 file) Times were determined via a variety of means – with issues of local solar time/mean solar time floating around. The timing issue improcved with pendulum clocks, but was not resolved until the mid 1700’s with the development of the chronometer. However there was no ‘program’ of dedicated lunar occultation observations.
2 Around 1920, Ernest Brown published his ‘Improved Lunar Ephemeris’ [which remained the basis of the lunar ephemeris until JPL developed their Development Ephemerides]. Brown suspected there was variability in the Earth’s rotation, and urged the observation of lunar occultations to determine whether this irregularity was real – which came to be accepted by around 1960.
3. RGO took on the task of collecting observations from around the world. As part of that role they undertook a comprehensive literature search for reported lunar occultations. These were essentially events observed after the period covered by Newcombe’s papers. They put all the data (1623 to 1980) into a consistent format and computerised it. This has formed a major part of the data held in Occult. However as explained in the Occult Help file (you really need to read the Occult Help to get a better background understanding) one of the magnetic tapes – containing the names of observers for 1943 to 1971 – got lost. As a result there are a large number of observations where the observer name is unknown
4. RGO bowed out of this role in 1980, and the International Lunar Occultation Center (set up as part of the Japanese Hydrological Division) took on the responsibility.
5. ILOC bowed out in 2005, and IOTA has taken on the role – via Occult.
Importantly, by 2005 the variability in the Earth’s rotation – which was the principle driver for the program of observing lunar occultations through almost all the 1900’s, was resolved beyond question – so that this rationale for observing lunar occultations ceased. The main rationale these days is measurement of double stars, and detection of new double stars – as well as building a collection of occultation light curves (which are archived at VizieR) useful for detecting whether a star is a point source.
Another historical issue is associated with the Watts charts of the lunar limb. These were developed at USNO by Chester Watts using photographs of the moon taken from several observatories. The aim was to be able to use lunar occultations for precise marine navigation. I suspect the objective was never fully realised. However the Watts charts remained the only tool to correct lunar occultations for the irregularities in the lunar limb – with major deficiencies in the polar regions of the moon. This changed with the results of the Japanese Kaguya mission, and subsequently the Lunar Reconnaisance Orbiter – where the lunar limb correction can be applied with confidence at a precision of a few meters. Indeed, as described in a paper by Dave Gault and myself in the January issue of the JOA, lunar occultations can now be used to validate the ‘whole-of-system’ timing accuracy