Mercury will reach half phase in its Dec 2009–Jan 2010 evening apparition. It will be shining brightly at mag -0.4.
From Cambridge , this apparition will not be one of the most prominent and very difficult to observe, reaching a peak altitude of 11° above the horizon at sunset on 23 Dec 2009.
Dec 2009–Jan 2010 evening apparition of Mercury
| 05 Nov 2009 | – | Mercury at superior solar conjunction |
| 18 Dec 2009 | – | Mercury at greatest elongation east |
| 21 Dec 2009 | – | Mercury at dichotomy |
| 22 Dec 2009 | – | Mercury at highest altitude in evening sky |
| 04 Jan 2010 | – | Mercury at inferior solar conjunction |
A graph of the phase of Mercury is available here.
Apparitions of Mercury
| 13 Jun 2009 | – | Morning apparition |
| 24 Aug 2009 | – | Evening apparition |
| 05 Oct 2009 | – | Morning apparition |
| 18 Dec 2009 | – | Evening apparition |
| 27 Jan 2010 | – | Morning apparition |
| 08 Apr 2010 | – | Evening apparition |
| 25 May 2010 | – | Morning apparition |
Observing Mercury
Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is lost in the Sun's glare much of the time.
It is observable for only a few weeks each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. These apparitions repeat roughly once every 3–4 months.
Mercury's phase
Mercury's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon.
Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times.
Mercury shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few days, only because Mercury's orbit is not quite perfectly aligned with the ecliptic.
Mercury's position
The coordinates of Mercury when it reaches dichotomy will be:
| Object | Right Ascension | Declination | Constellation | Angular Size |
| Mercury | 19h26m20s | 23°10'S | Sagittarius | 7.3" |
| Sun | 17h59m | 23°26'S | Sagittarius | 32'30" |
The coordinates above are given in J2000.0.
The sky on 25 Apr 2024
| The sky on 25 April 2024 | ||||||||||||||||||||||||||||||||||
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95% 17 days old |
All times shown in EDT.
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Warning
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.
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.
Related news
| 18 Dec 2009 | – Mercury at greatest elongation east |
| 22 Dec 2009 | – Mercury at highest altitude in evening sky |
| 21 Jan 2010 | – Mercury at highest altitude in morning sky |
| 27 Jan 2010 | – Mercury at greatest elongation west |
Image credit
© NASA/JPL/MESSENGER