Mercury will reach half phase in its Jan–Feb 1990 morning apparition. It will be shining brightly at mag -0.1.
From Columbus , this apparition will not be one of the most prominent and tricky to observe, reaching a peak altitude of 14° above the horizon at sunrise on 26 Jan 1990.
Jan–Feb 1990 morning apparition of Mercury
| 08 Jan 1990 | – | Mercury at inferior solar conjunction |
| 24 Jan 1990 | – | Mercury at highest altitude in morning sky |
| 26 Jan 1990 | – | Mercury at dichotomy |
| 31 Jan 1990 | – | Mercury at greatest elongation west |
A graph of the phase of Mercury is available here.
Apparitions of Mercury
| 28 Aug 1989 | – | Evening apparition |
| 10 Oct 1989 | – | Morning apparition |
| 23 Dec 1989 | – | Evening apparition |
| 31 Jan 1990 | – | Morning apparition |
| 13 Apr 1990 | – | Evening apparition |
| 31 May 1990 | – | Morning apparition |
| 11 Aug 1990 | – | 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 | 18h51m50s | 21°01'S | Sagittarius | 7.5" |
| Sun | 20h34m | 18°41'S | Capricornus | 32'29" |
The coordinates above are given in J2000.0.
The sky on 23 Nov 2024
| The sky on 23 November 2024 | ||||||||||||||||||||||||||||||||||
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42% 22 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
| 25 Jan 1990 | – Mercury at highest altitude in morning sky |
| 31 Jan 1990 | – Mercury at greatest elongation west |
| 13 Apr 1990 | – Mercury at highest altitude in evening sky |
| 13 Apr 1990 | – Mercury at greatest elongation east |
Image credit
© NASA/JPL/MESSENGER