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BAA Observing calendar

Mercury at inferior solar conjunction

Sunday, 2019, July 21 - 13:28

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°57' 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 0.58 AU from the Earth, making it appear with its largest angular size. If it could be observed, it would measure 11.6 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 07h57m00s +15°39' Cancer 11.6"
Sun 08h01m +20°31' Cancer 31'28"

The coordinates above are given in J2000.0.

This entry in the observing calendar was provided by In-The-Sky.org

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