Mercury will reach half phase in its Oct 2007 evening apparition. It will be shining brightly at mag 0.1.
From London , this apparition will be unobservable, reaching a peak altitude of 4° above the horizon at sunset on 9 Sep 2007.
Oct 2007 evening apparition of Mercury
| 11 Sep 2007 | – | Mercury at highest altitude in evening sky |
| 29 Sep 2007 | – | Mercury at greatest elongation east |
| 04 Oct 2007 | – | Mercury at dichotomy |
| 24 Oct 2007 | – | Mercury at inferior solar conjunction |
A graph of the phase of Mercury is available here.
Apparitions of Mercury
| 21 Mar 2007 | – | Morning apparition |
| 02 Jun 2007 | – | Evening apparition |
| 20 Jul 2007 | – | Morning apparition |
| 29 Sep 2007 | – | Evening apparition |
| 08 Nov 2007 | – | Morning apparition |
| 22 Jan 2008 | – | Evening apparition |
| 03 Mar 2008 | – | 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 | 14h10m20s | 16°35'S | Virgo | 7.4" |
| Sun | 12h39m | 4°17'S | Virgo | 31'58" |
The coordinates above are given in J2000.0.
The sky on 19 May 2024
| The sky on 19 May 2024 | ||||||||||||||||||||||||||||||||||
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89% 11 days old |
All times shown in BST.
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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
| 29 Sep 2007 | – Mercury at greatest elongation east |
| 08 Nov 2007 | – Mercury at highest altitude in morning sky |
| 08 Nov 2007 | – Mercury at greatest elongation west |
| 22 Jan 2008 | – Mercury at greatest elongation east |
Image credit
© NASA/JPL/MESSENGER