Mercury will reach half phase in its Dec 2011–Jan 2012 morning apparition. It will be shining brightly at mag -0.3.
From Fairfield , this apparition will be well placed but tricky to observe, reaching a peak altitude of 16° above the horizon at sunrise on 21 Dec 2011.
Dec 2011–Jan 2012 morning apparition of Mercury
| 04 Dec 2011 | – | Mercury at inferior solar conjunction |
| 18 Dec 2011 | – | Mercury at dichotomy |
| 20 Dec 2011 | – | Mercury at highest altitude in morning sky |
| 23 Dec 2011 | – | Mercury at greatest elongation west |
A graph of the phase of Mercury is available here.
Apparitions of Mercury
| 19 Jul 2011 | – | Evening apparition |
| 03 Sep 2011 | – | Morning apparition |
| 14 Nov 2011 | – | Evening apparition |
| 23 Dec 2011 | – | Morning apparition |
| 05 Mar 2012 | – | Evening apparition |
| 18 Apr 2012 | – | Morning apparition |
| 30 Jun 2012 | – | Evening 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 | 16h15m30s | 18°38'S | Scorpius | 7.3" |
| Sun | 17h43m | 23°23'S | Sagittarius | 32'30" |
The coordinates above are given in J2000.0.
The sky on 22 Nov 2024
| The sky on 22 November 2024 | ||||||||||||||||||||||||||||||||||
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45% 21 days old |
All times shown in EST.
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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.
Related news
| 18 Nov 2011 | – Mercury at highest altitude in evening sky |
| 20 Dec 2011 | – Mercury at highest altitude in morning sky |
| 23 Dec 2011 | – Mercury at greatest elongation west |
| 05 Mar 2012 | – Mercury at highest altitude in evening sky |
Image credit
© NASA/JPL/MESSENGER