Mercury at inferior solar conjunction

Dominic Ford, Editor
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The sky at

Mercury will pass very close to the Sun in the sky as its orbit carries it between the Sun and Earth.

This occurs once in every synodic cycle of the planet (116 days), and marks the end of Mercury's apparition in the evening sky and its transition to become a morning object over the next few weeks.

At closest approach, Mercury will appear at a separation of only 4°13' from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare.

Mercury will also pass perigee – the time when it is closest to the Earth – at around the same time, since it will lie on exactly the same side of the Sun as the Earth in the Solar System. It will move to within a distance of 0.62 AU from the Earth, making it appear with its largest angular size. If it could be observed, it would measure 10.8 arcsec in diameter, whilst appearing completely unilluminated.

The exact position of Mercury at the moment it passes solar conjunction will be:

Object Right Ascension Declination Constellation Angular Size
Mercury 10h15m40s +06°16' Sextans 10.8"
Sun 10h21m +10°12' Leo 31'39"

The coordinates above are given in J2000.0.

The sky on 26 August 2017
Twilight ends
Twilight begins

5-day old moon
Waxing Crescent


5 days old

Rise Culm. Set
Mercury 06:24 12:48 19:13
Venus 03:25 10:42 17:59
Moon 11:19 16:52 22:26
Mars 05:21 12:17 19:14
Jupiter 10:12 15:50 21:28
Saturn 15:11 19:52 00:37
All times shown in EDT.


Never attempt to point a pair of binoculars or a telescope at an object close to the Sun. Doing so may result in immediate and permanent blindness.


The circumstances of this event were computed using the DE405 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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12 Sep 2017  –  Mercury at greatest elongation west
14 Sep 2017  –  Mercury reaches highest point in morning sky
23 Nov 2017  –  Mercury at greatest elongation east

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