10 replies to this topic

[KiwiRay]

Now for a real challenge...I don't see a lot of images posted of Mercury from any size scope, let alone images captured using small scopes, so it may be that this is not a popular topic, but it is possible to capture surface features with a small scope on Mercury, and I'm sure there must be someone else out there who has tried and has images to share.

 

Yesterday evening, Mercury was close to the crescent Moon, making it easy to align my Nexstar 6SE on the Moon, focus, and then slew to Mercury.  The day before I aligned on the Sun, which was further from the planet in the sky, and had no luck finding Mercury (aligning on a single solar system body isn't very accurate).  The resulting image is by no means impressive, but comparing to the WinJUPOS simulation, it does look like I captured some albedo features.  I used an ASI224MC camera with 2x Barlow, ADC and 610 nm filter.  Imaging time was around 6:40pm, and seeing was pretty terrible.  I'd like to think that in good seeing, someone could do much better with a 6" scope.

 

[rehling]

Very timely!

 

I've put quite a bit of effort into daytime imaging of Mercury since October, but none of my results have been as nice as yours. I've used a 685 nm filter, which sacrifices resolution to compensate for the (usually bad) seeing, and introduces diffraction artifacts. I suppose the best results for small telescopes and Mercury would be to use blue or green filters during the daytime and try for an opportunity with unusually good seeing.

 

One of my best tactics was to find a place with a narrow view of the southern sky and use a date where Mercury is far east of the Sun. Then lock the scope on the Sun when it passes through the notch – this will orient the telescope. Now wait for Mercury to move into sight, which will be about 90 minutes after the Sun moves out of sight; this will allow the telescope to cool for the Mercury observation. On a couple of occasions, Mercury has appeared very nice through the eyepiece, like a gibbous Moon. I have looked at Mercury through the eyepiece at a low altitude after sunset many times, and the combination of poor seeing and extinction have almost always compromised the view tremendously. 

 

Probably my best image was from 20170312, when a dark feature was apparent in the upper left, and the bright area to its right is the Caloris Basin. My image is on the left and a comparison image made from Messenger imagery on the right.

 

I intend to make a map from images I took on five of the last six elongations of Mercury, but this has been a long process, now nearing an end.

 

I also attached a gif showing Mercury's phases changing from the late May elongation. Diffraction artifacts abound.

 

I have a few more results to post as I go through my archival data and reprocess it better.

 

[KiwiRay]

Nice work, rehling - I had wondered if you were imaging Mercury, given all the work you've put into Venus.  I wish I was able to try more often, but the timing of evening apparitions isn't great.  I have to wait for the Sun to go behind my neighbour's roof, by which time it's near dinner time and I have two hungry young children running around the back yard - not the optimal environment for imaging a sometimes hard-to-find planet.

[rehling]

Thanks, KiwiRay! Mercury has three great appeals to me: I live in a white zone with seasonal fog that can provide many clear days followed by foggy evenings. Imaging Mercury in the daytime makes both of those problems irrelevant. The third appeal is that Mercury imaging opportunities turn over on a much faster cycle than any other planet. The switch to daytime has put Mercury in some incredible altitudes for me, as high as 72°, and it feels like a totally new object from the blazing, shimmering thing I've seen through the eyepiece after sunset / before sunrise. It can basically become a very convenient object instead of the highly inconvenient object it is for evening observers, but only if you can get to your telescope in the daytime.

 

Transparency is also a huge factor. Clear days here often have great transparency. When I look at my daytime IR Mercury images, sometimes the background looks gray, and sometimes nearly black. I've written my own software to subtract the sky background, because that can otherwise be a big problem for frame alignment.

[rehling]

Here was another result I was going for. On 20161005, I took daytime pictures of Mercury with several filters. It was at an altitude of 50° and transparency was good.

 

The raw RGB is on the left. Then I computed the average background sky color from that frame and subtracted it from the raw image to get the result on the right. This is, I think, the only color picture of Mercury taken from the Earth without serious extinction (i.e., reddening) due to low altitude that I have ever seen.

 

 

I think this matches fairly well a global "true color" image taken by Messenger (the upper right image in the array of different color mixes).

 

http://messenger.jhu...-image-234.html

 

Another approach to this that I've considered but never tried is to take a picture of Mercury in an evening sky, then take a picture of nearby stars, and measure how much extinction due to low altitude has reddened those stars, then apply the appropriate adjustment to Mercury. An even easier effort could be made when Mercury is in close conjunction with another planet… I saw it in the eyepiece with Venus shortly before I got my first astrophotography camera, and that would have been a good opportunity to try that approach.

Edited by rehling, 31 July 2017 - 09:04 PM.

[KiwiRay]

Mercury from 5:43pm this afternoon.  I aligned the scope on Venus (easy to find before sunset with binoculars) and then slewed to nearby Mercury.  Terrible seeing conditions, and I didn't have time to put on the IR filter as it was about to go behind trees.  Still, the blurred WinJUPOS simulation (left in image below) confirms I captured some albedo features, so I'm happy!

 

[Lacaille]

That's good going! Your image seems crisper than the simulation you used for checking accuracy!

[KiwiRay]

Thanks!  I blurred the simulation so that the clarity resembled that of my image, which made it easier to compare and see if I'd really captured surface detail or not.

[Lacaille]

Ah! That explains it! I was checking ahead on Stellarium and worked out we have a good period in June-July with Mercury and Venus at quite high altitudes in July.  If I can image Mercury, I only need Neptune to complete my set!

[rehling]

It took me awhile to realize this, but daytime planets are more or less always at great altitudes near the summer solstice and nighttime planets at poor altitudes then, and winter is the opposite. But for detailed planning ahead, the websites and apps are essential!

[KiwiRay]

From this afternoon.  Nexstar 6SE + 2x Barlow + ADC.  ASI224MC camera.