Mercury: Picture Gallery

The best viewing for 20yrs!

The closest planet to the Sun, Mercury is an exceedingly difficult photographic subject as it is a very small world, and so not particularly bright, and always very close to the Sun in the sky. Because it keeps close to the Sun it is never visible other than just after sunset or just before sunrise and even then it is low down on the horizon. Although the geometry of its orbit means you should be able to observe it after sunset for three brief periods per year, in practice it often won't be high enough in the sky to make observation practical. I had seen it a couple of times through binoculars but never properly observed it through a telescope.

This is usually about all you see of Mercury and even then I've had to enhance the image slightly to make it visible! (half-way across, a quarter of the way down). A shot taken with the digital camera at 10:20pm on 10th June 2006. I couldn't see the planet except through binoculars so was quite glad to find it in the frame when examining the picture!

Just occasionally though, everything comes together to make observing the innermost planet quite straightforward. At dusk in the beginning of February 2007 Mercury was at eastern elongation (i.e. at the maximum angle away from the Sun for that orbit, as seen from the Earth); was fairly close to Venus (which made finding it much easier); was reasonably high in the sky (because its path towards the horizon is at quite a steep angle at that time of year), and (more miraculously!) the skies were almost totally clear. I was thus able to see it "naked eye" quite easily: this is a pretty rare event.

And here it is, a gleaming point of light against the blue sky at 5:20pm on 6th February. Mercury was not so close to Venus as to call the event a conjunction but they did make a fine sight nonetheless. The next day the pair were still nicely visible, this time with Mercury skimming the roof-tops at 5:45pm: note how much brighter they are against the darker sky.

Recognise the tree at bottom left in this shot? Yep - it's the same one as in the first two of the images above (different television aerial though!). This picture was taken on 24th January 2008 and shows Mercury having returned to almost the same place in the evening sky. It's not as close as it looks, as this shot was taken from a somewhat different viewpoint and at a slightly different time from those above, but does suggest there might be a periodic element to Mercury's movements.
To see whether this is true, click here.

In early May 2008 Mercury was again near to eastern elongation but not quite so favourably placed as in 2007. A long spell of clear weather made observation worthwhile though, particularly as the planet was very close to an incredibly thin crescent Moon on the 6th. The first image shows it as an easy naked-eye object on the 5th.

Then on the 6th we had the conjunction. There's a "standard" picture of it on the Conjunctions page so here I give a rather more dramatic view! The pair are so close to the horizon that both have turned an orange colour more reminiscent of the setting Sun.

Conditions were still good on the 11th and here is a montage of five images showing Mercury slowly heading for the western twilight in just over ¹/4hr.

And a "super-montage" of nine images taken on the 17th over a period of just under ¹/2hr.

Eagle-eyed observers will have noted that the angle to the horizon of the two sets of images above is not the same. Most of this is due to the different camera angle (the telegraph pole should be upright in both images!) but not all. I found that rotating the first image by 4deg would stand the pole upright but when the tracks were overlaid they did not exactly line up - see the images below.
[ The "line of descent" on the 11th is marked in red, that on the 17th in green ]

Firstly, a composite image with an upright telegraph pole in both shots. The (extended) track from the 11th is seen to be slightly "steeper" than that from the 17th. And here we see that if the image from 11th May is rotated by only 3¹/4deg. rather than 4deg the tracks line up. This means that the angle between the tracks in the left-hand image is ³/4 deg.

The difference of ³/4deg. is not, in fact, some artefact of the way I took the photographs but a real effect. While most people know that the Sun (and therefore all other objects in the sky) sets at a steeper angle as you move from pole to equator there is also an effect caused by the tilt of the Earth's axis, which decreases the setting angle the closer the date is to the solstices. In the UK the "solar parallactic angle", as it is called, changes by something over 7deg. from equinox to solstice. Between the dates of the images in the montages it decreased by 0.737deg, which is pleasingly close to the amount measured from the composites.

I said at the start that Mercury is difficult to observe because it tends to be close to the horizon. Its path across the sky does vary quite a lot though, so some viewing opportunities are much better than others. At the end of April 2009 it was at its greatest altitude during a 20yr period - not only that, it was also very close to a thin crescent Moon which was itself even closer to the "Seven Sisters" comprising the constellation of the Pleiades. Normally this would mean I get thick cloud (!), but no - just for once I was blessed with perfectly clear skies.

I've put a picture of the conjunction itself on the "Conjunctions and Occultations" page but the one to the left here shows just how high Mercury was on this date (26th April) - 14degrees in this image, in fact, taken just 20mins after sunset.

There was another good opportunity to view in March 2011 - exactly at the equinox, in fact. Even better, Mercury was in conjunction with Jupiter at this time. It was cloudy on the days near minimum approach unfortunately, so by the time of this image (18th March, 3days afterwards) the separation was already well over 4deg. Jupiter is just above the tree-line, by the way.

It is generally true that the situation for evening viewings is best around the spring equinox (for observers in the northern hemisphere) because it is then that the ecliptic (the path of the Sun and planets across the sky) makes the greatest angle with the horizon. There are other factors to take into consideration though, such as the distance of Mercury from the Sun and its position on its rather tilted orbit, so how good a "good opportunity" is will vary somewhat. "Very best" opportunities will re-occur at intervals of 6 and then 7yrs because after these periods the Earth and Mercury are very nearly in the same positions again. Thus the best opportunity before 25th April 2009 was 16th April 2003 and the next one was on 18th April 2016.

The images in this composite were taken a little later than the one above, and from a slightly different angle. They show Mercury at intervals of 80sec as it approached the horizon about an hour after sunset. Though not directly comparable to the similar composites above (it's not actually the same telegraph pole!) the setting angle is steeper in this image due to the closer proximity to the equinox. To see this, click or tap on the image to superimpose the tracks (and again to remove them). Theory says that the difference in slope between the green (17th May) and pink (18th March) lines should be 4.8deg.

All the images so far were taken with the digital camera of course, but a favourable circumstance at the end of June 2005 gave me a chance to observe Mercury with the reflector telescope (plus webcam). This occasion was a very close conjunction ("coming together") with the bright planet Venus - being so near to Venus in the sky, Mercury was much easier to spot. Even so, I never managed to definitely see it without binoculars and it was only just visible in the finder telescope due to the brightness of the sky so soon after sunset. Planetary conjunctions are not that uncommon, but one as close as this is fairly unusual - when I observed them Mercury & Venus were separated by less than one-sixth of the diameter of the full Moon. Such is the speed of movement of Mercury, however, that in just the half hour I was taking photographs they separated by a sufficient extra distance to be clearly noticeable - see below. To find out more about conjunctions, click here.

Mercury is so small (smaller than Jupiter's moon Ganymede and Saturn's moon Titan) that even though it is relatively close to the Earth its image is correspondingly small and thus very susceptible to distortions caused by atmospheric effects and camera artefacts. Quite a bit of image processing was thus needed to get a good result but the final picture shows the planet quite nicely.

This image is shown at the same scale as the other shots in the gallery to enable direct comparisons to be made. Even at this size it is obvious that the planet is not fully illuminated. An 8-times expanded view clearly shows that Mercury was at about half-phase (60%, to be precise). The "boomerang" shape is because the grid-like structure of the camera sensor tends to emphasise small images horizontally and vertically (the image has been rotated for viewing).

As mentioned above, Mercury has a very rapid "proper motion" - its true movement across the sky, as opposed to the apparent movement due to the Earth's rotation. The image of the 27th June conjunction below shows this dramatically, being a composite of two shots taken about 30mins apart. In this time, Mercury has moved "up and left" relative to Venus (which is considerably over-exposed). This rapid motion is one of the reasons that opportunities to observe Mercury are so limited: even under favourable conditions, about 3wks after it has appeared from behind the Sun it has vanished into the twilight again.

I also took pictures of the conjunction with a film camera, to give a wider angle view than was possible with the telescope. This one was taken with a 600mm lens plus 1.4x multiplier (I couldn't find the 2x doubler!), giving an effective 840mm. I have added the grey circle, which represents the size of a full Moon at the same scale, to show how close together the two were.

An enlargement shows that even with the film camera it is obvious that Venus is not fully illuminated: it was actually at about 90% phase. It also shows well how much larger and brighter Venus was than Mercury. On the other hand, a comparison with a webcam image (scaled and rotated to match the film image) shows how much the film image over-states the size of the planets' discs, despite them appearing very small in the picture. Hence the use of telescopes and digital techniques!

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And here it is, a gleaming point of light against the blue sky at 5:20pm on 6th February.	Mercury was not so close to Venus as to call the event a conjunction but they did make a fine sight nonetheless.	The next day the pair were still nicely visible, this time with Mercury skimming the roof-tops at 5:45pm: note how much brighter they are against the darker sky.

	In early May 2008 Mercury was again near to eastern elongation but not quite so favourably placed as in 2007. A long spell of clear weather made observation worthwhile though, particularly as the planet was very close to an incredibly thin crescent Moon on the 6th. The first image shows it as an easy naked-eye object on the 5th.
	Then on the 6th we had the conjunction. There's a "standard" picture of it on the Conjunctions page so here I give a rather more dramatic view! The pair are so close to the horizon that both have turned an orange colour more reminiscent of the setting Sun.

	Conditions were still good on the 11th and here is a montage of five images showing Mercury slowly heading for the western twilight in just over ¹/4hr.
	And a "super-montage" of nine images taken on the 17th over a period of just under ¹/2hr.


Firstly, a composite image with an upright telegraph pole in both shots. The (extended) track from the 11th is seen to be slightly "steeper" than that from the 17th.	And here we see that if the image from 11th May is rotated by only 3¹/4deg. rather than 4deg the tracks line up. This means that the angle between the tracks in the left-hand image is ³/4 deg.


This image is shown at the same scale as the other shots in the gallery to enable direct comparisons to be made. Even at this size it is obvious that the planet is not fully illuminated.	An 8-times expanded view clearly shows that Mercury was at about half-phase (60%, to be precise). The "boomerang" shape is because the grid-like structure of the camera sensor tends to emphasise small images horizontally and vertically (the image has been rotated for viewing).

	I also took pictures of the conjunction with a film camera, to give a wider angle view than was possible with the telescope. This one was taken with a 600mm lens plus 1.4x multiplier (I couldn't find the 2x doubler!), giving an effective 840mm. I have added the grey circle, which represents the size of a full Moon at the same scale, to show how close together the two were.

An enlargement shows that even with the film camera it is obvious that Venus is not fully illuminated: it was actually at about 90% phase. It also shows well how much larger and brighter Venus was than Mercury.	On the other hand, a comparison with a webcam image (scaled and rotated to match the film image) shows how much the film image over-states the size of the planets' discs, despite them appearing very small in the picture. Hence the use of telescopes and digital techniques!