Mercury's 88-day orbit around the Sun will carry it to its closest point to the Sun – its perihelion – at a distance of 0.31 AU from the Sun.
Unlike most of the planets, which follow almost exactly circular orbits around the Sun only varying in their distance from the Sun by a few percent, Mercury has a significantly elliptical orbit.
Its distance from the Sun varies between 0.307 AU at perihelion (closest approach to the Sun), and 0.467 AU at aphelion (furthest recess from the Sun). This variation, of over 50%, means that its surface receives over twice as much energy from the Sun at perihelion as compared to aphelion.
However, this makes little difference to Mercury's telescopic appearance, since little if any detail on its surface can be resolved by ground-based telescopes. Although its changing seasons have an incredible effect upon its surface temperatures, there is little change that is visible to amateur observers.
The position of Mercury at the moment it passes perihelion will be:
| Object | Right Ascension | Declination | Constellation | Angular Size |
| Mercury | 10h29m40s | 10°32'N | Leo | 6.6" |
| Sun | 11h32m | 2°55'N | Leo | 31'48" |
The coordinates above are given in J2000.0.
From Cambridge, Mercury will be visible in the dawn sky, rising at 04:52 (EDT) – 1 hour and 30 minutes before the Sun – and reaching an altitude of 11° above the eastern horizon before fading from view as dawn breaks at around 06:02.
The sky on 15 Sep 2017
| The sky on 15 September 2017 | ||||||||||||||||||||||||||||||||||
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20% 25 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
| 13 Sep 2017 | – Mercury at highest altitude in morning sky |
| 23 Nov 2017 | – Mercury at greatest elongation east |
| 28 Nov 2017 | – Mercury at highest altitude in evening sky |
| 29 Dec 2017 | – Mercury at highest altitude in morning sky |
Image credit
© NASA/JPL/MESSENGER