Mercury at perihelion

Fri, 15 Sep 2017 at08:28 EDT(10 days ago)
12:28 UTC

Dominic Ford, Editor
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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 10h29m40s +10°32' Leo 6.6"
Sun 11h32m +02°55' Leo 31'48"

The coordinates above are given in J2000.0.

From Ashburn (click to change), Mercury will be difficult to observe as it will appear no higher than 12° above the horizon. It will be visible in the dawn sky, rising at 05:22 (EDT) – 1 hour and 28 minutes before the Sun – and reach an altitude of 12° above the eastern horizon before fading from view as dawn breaks at around 06:31.

The sky on 15 September 2017
Sunrise 06:50
Sunset 19:17
Twilight ends
Twilight begins

25-day old moon
Age of Moon
25 days

All times shown in EDT.
Rise Culm. Set
Mercury 05:23 12:01 18:38
Venus 04:28 11:18 18:08
Moon 01:59 09:06 16:14
Mars 05:27 12:04 18:41
Jupiter 09:27 15:02 20:37
Saturn 14:05 18:52 23:38


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.

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