The Moon will pass in front of Neptune, creating a lunar occultation visible from parts of Oceania.
Lunar occultations are only ever visible from a small fraction of the Earth's surface. Since the Moon is much closer to the Earth than other celestial objects, its exact position in the sky differs depending on your exact location on Earth due to its large parallax. The position of the Moon as seen from two points on opposite sides of the Earth varies by up to two degrees, or four times the diameter of the full moon.
This means that if the Moon is aligned to pass in front of a particular object for an observer on one side of the Earth, it will appear up to two degrees away from that object on the other side of the Earth.
On this occasion, no occultation will be visible from Cambridge.
The map below shows the visibility of the occultation across the world. Separate contours show where the disappearance of Neptune is visible (shown in red), and where its reappearance is visible (shown in blue). Solid contours show where each event is likely to be visible through binoculars at a reasonable altitude in the sky. Dotted contours indicate where each event occurs above the horizon, but may not be visible due to the sky being too bright or the Moon being very close to the horizon.
Outside of the contours, the Moon does not pass in front of Neptune at any time, or is below the horizon at the time of the occultation.
The map below can be downloaded in PNG , PDF or SVG format. A KMZ file , is also available, which can be opened in Google Earth to provide a higher resolution map.
The position of Neptune at the moment of the occultation will be as follows:
| Object | Right Ascension | Declination | Constellation | Magnitude | Angular Size |
| Neptune | 22h54m30s | 7°58'S | Aquarius | 7.8 | 0'02" |
The coordinates above are given in J2000.0.
| The sky on 03 October 2017 | ||||||||||||||||||||||||||||||||||
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96% 13 days old |
All times shown in EDT.
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Source
The circumstances of this event were computed using the DE430 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).
This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.
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| 05 Sep 2017 | – Neptune at opposition |
| 07 Sep 2018 | – Neptune at opposition |
| 10 Sep 2019 | – Neptune at opposition |
| 11 Sep 2020 | – Neptune at opposition |
Image credit
The Moon in conjunction with Venus and Jupiter, with the Very Large Telescope in the foreground. Image © Y. Beletsky, ESO, 2009.