Mercury at perihelion

Dominic Ford, Editor
From the Inner Planets feed

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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 09h44m20s +14°36' Leo 6.2"
Sun 10h44m +07°57' Leo 31'42"

The coordinates above are given in J2000.0.

From Ashburn, Mercury will be difficult to observe as it will appear no higher than 10° above the horizon. It will be visible in the dawn sky, rising at 05:15 (EDT) – 1 hour and 23 minutes before the Sun – and reaching an altitude of 10° above the eastern horizon before fading from view as dawn breaks around 06:19.

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The sky on 02 September 2018
Twilight ends
Twilight begins

22-day old moon
Waning Gibbous


22 days old

Rise Culm. Set
Mercury 05:17 12:09 19:00
Venus 10:27 15:48 21:09
Moon 23:27 06:23 13:18
Mars 17:58 22:29 03:03
Jupiter 12:13 17:21 22:30
Saturn 15:47 20:31 01:19
All times shown in EDT.


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.


The circumstances of this event were computed using the DE405 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 Aug 2018  –  Mercury reaches highest point in morning sky
06 Nov 2018  –  Mercury at greatest elongation east
11 Nov 2018  –  Mercury reaches highest point in evening sky
14 Dec 2018  –  Mercury reaches highest point in morning sky

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