Section report for June and July 2016
This reporting period has produced a number of very good quality observations but with the Jupiter season virtually over and with Mars and Saturn at low elevation the total number of observations was relatively small compared with earlier in the year. With this in mind I thought I would start with a quick summary of the Jupiter and Mars observations for 2016 before looking at individual contributions.
Jupiter has been active with the North Equatorial Belt (NEB) showing a marked expansion towards the north, partially engulfing the large storm White Spot Zulu (WSZ) making it very obvious whenever it was on the visible disc. The NEB tends to have these regular expansion then contraction periods on a variable time-scale of three to five years. In this case the expansion looked set to follow the normal pattern and to be visible around the whole planet but, unexpectedly, the expansion stalled before covering more than half the circumference. What is apparently happening is a partial dispersal of the thin white ammonia-ice cloud that normally covers the northern edge of the NEB, revealing the darker cloud beneath as an ‘expansion’ of that dark cloud. In this apparition the high ammonia cloud failed to clear around the whole circumference, which is unusual, and one can only speculate how this may relate to future cycles of expansion.
In the south the large turbulent rift in the South Equatorial Belt (SEB), that follows behind the Great Red Spot (GRS), initially showed marked activity with bright spots of new storm activity being noted, particularly in methane-band images contributed by section members. Then these storms subsided suddenly in early June making the turbulence much less obvious. This might lead to a general fading of the SEB as reflective high cloud reforms over the more stable atmosphere below; something to watch out for in the winter.
The GRS does not seem to have shrunken in size noticeably during this apparition and has darkened slightly making it more obvious while its former rival red storm, Oval BA, has become very pale and hard to find in an empty region that used to contain the South Temperate Belt (STB). This belt has only a few ghost features remaining and this is also rather unusual, so it might be a good bet to predict a revival of the STB by early winter.
If we now look at Mars we can say that features we might reasonably expect to see according to the Martian season have been on view. For early 2016 Mars has been experiencing a late northern-hemisphere summer / southern winter with June marking the start of autumn for the north and spring for the south. These seasons produced a shrinking in the northern polar ice cap and a build-up of cloud visible on the up-slopes of high ground and at the morning and evening terminators. The frost in the deep Hellas basin disappeared and a thin ‘hood’ of cloud appeared around the South Pole although the polar ice-cap itself was not visible being slightly tilted away from us. Some features became more obvious, notably the Argyre Basin brightened and a large ‘tick’ shape of yellow dust appeared near the Elysium plateau causing speculation that a dust storm was forming as has often been seen in Martian southern-hemisphere springtime. So far this has not proven to be the case so perhaps this is a new feature for future observation.
I would like to mention here the perceived difficulty of making observations of a planet when it is very low in the sky, as is Mars and Saturn at the moment. It has often been thought that we are wasting our time if we want to make detailed observations of a target below 30 degrees in elevation. With this in mind I would like to quote Martin Lewis from one of his emails sent in this reporting period:-
“Overall I have been extremely pleased with my low altitude imaging this apparition for both Mars and Saturn. The imaging opportunities have been limited but with a range of cameras, IR filters, Barlows, and an ADC at my disposal I have been able to make the most of difficult conditions. To be honest (until I saw the results I was getting) I had written off Saturn for this year and for the next 5 years or so.”
Martin refers to use of an Atmospheric Dispersion Corrector (ADC) and this has made a very real difference to low-altitude observation, noticeably improving the quality of the results gained visually and photographically by a number of regular contributors. These devices were once very expensive but are now available for around £125 and should be a consideration for any amateur who wants to extend the period of observation available to them.
Looking at the contributions from the section in this period I will start with Mars. The distribution of images and reports shows a rush of contributions for the first week of June and only sporadic contributions from then on. The period 1st to the 8th gave us reports from Alexei Pace, Steve Norrie, Simon Kidd, Dave Finnigan, Graham Sparrow, Carl Bowron, Dave Tyler, Matthew Barrett, Larry Todd and a new contributor, Mark Whitcutt; Thank you Mark. In this period the Mare Acidalium and Mare Erythraeum were well displayed with Alexei Pace catching detail down to the level of the Axia Pallas and Steve Norrie catching pale cloud on the terminator near the Tharsis bulge. Simon Kidd and Dave Tyler took images with an almost identical presentation on the 5th and 6th respectively showing the formation of the south-polar hood of cloud and Sinus Sabaeus as very dark against a featureless Eden. Steve’s image from a little later the same night shows bright cloud forming over Tempe, biting into the edge of Mare Acidalium; Dave Finnigan’s image taken at 2216 UT also shows all these features though it may be noted that the use of filtered images on a monochrome camera, as used by Dave Tyler, more clearly revealed atmospheric cloud, particularly through a blue filter, when compared with images made using a colour camera.
Carl Bowron was able to catch similar levels of detail using a six-inch achromatic refractor, if at a smaller image scale, which follows on from the work done by Robin Scagell in the last reporting period, confirming smaller aperture instruments work well when absolute detail is compromised by low elevation viewing. Graham Sparrow sent a most excellent sketch of Mars from the 6th of June, as did Matthew Barrett, for the 4th, 5th and 6th and Alan Heath as part of his chain of 11 observations that finished on the 17th of July. Alan noted relative intensity of major surface detail (as did Matthew) and he also described bright patches in both Hellas and over the Argyre Planitia, the latter confirmed photographically as cloud by other section members.
Later Mars contributions were made by Larry Todd on the 16th of June and by Martin Lewis on the 3rd and 17th. Larry sends his images in from New Zealand and, as such, they are taken around 12 hours later than images made in the UK and therefore show a very different face to that visible here. His early images show very bright cloud sitting over Elysium as well as frontal cloud around the North Pole and the south polar hood and with excellent surface detail. In contrast Martin’s image from the 3rd of July has the Tharsis shield volcanoes near the central meridian and dark patches marking volcanic peaks in the area. It also shows a bright patch of frontal cloud near the North Pole; this type of cloud is currently being studied by professionals trying to more fully understand the weather patterns on Mars.
Saturn reached opposition on the 3rd of June and I was very happy with the number of section members who attempted this low altitude target, especially so given the low levels of contrast normally visible in its cloud systems. Individual observations came from Steve Norrie, Dave Finnigan, Martin Lewis, Matthew Barrett, Carl Bowron, Alexei Pace, Mark Whitcutt and Dave Tyler with a cluster of observations shortly after opposition and with four more then spread through late June and into July. No one was able to report an obvious Seeliger Effect around the night of opposition. This is a noticeable brightening of the ring system usually explained by the shadows cast by particles within the rings exactly aligning behind the particles themselves. As a result the shadow is hidden from our point of view and the brightness per unit area of ring observed increases. The same effect can be seen during a full moon when there are no shadows cast by visible crater walls or hills causing the brightness of any given area of the Moon to increase. In any case the section was not able to observe during the night of opposition so any Seeliger effect went unseen.
Steve’s images from the 5th and 6th of June shows very obvious zonal banding on the planetary disc along with a sharp shadow cast by the planet on the rings behind it; something also seen in Matthews drawings over the same period. Dave’s images, also from the 5th of June, show a dark belt around the North Pole which stops only slightly short of resolving the hexagonal cloud pattern that sits at these high latitudes. Like Dave, Martin Lewis used an ADC on his Saturn images of that night and he used a 642 Nm ‘Band Pass’ filter (passing 642 to 742 Nm wavelength in the red and near infrared) as a luminance layer to lay on top of his colour data. With Saturn at just 18 degrees of elevation he caught a dark cloud patch over the North Pole itself, something he repeated on the 17th of July. Carl Bowron, also on the 5th of June, used a NexImage 5 colour camera in a wide-view resolving the Cassini Division around the entire visible ring and a brightening within the ‘B’ ring as well as surface banding; Mark Whitcutt’s image shows a wider if similar view.
Alexei Pace was imaging from Malta so luckily didn’t have quite so low a target to contend with; he managed to resolve hints of the Encke Division around the perimeter of the outer ‘A’ ring. Martin Lewis also managed to capture excellent images on the 3rd and 17th of July in which the south pole of Saturn can just be glimpsed looking through the Cassini Division in the rings. His methane-band image of the 3rd shows just how dark Saturn is at these frequencies with only a faint glow visible around the equator; in stark contrast to the brightness of the surrounding rings. Finally Dave Tyler sent an image from the 31st of July catching a faint hint of the inner ‘D’ or Crepe Ring as it softens the view of the planet’s surface behind it.
With space running out I must mention the image taken of Venus by Carl Bowron on the 17th of July when the planet was just 10 degrees from the Sun and showing a 98% phase, and also his images of Jupiter, along with those of Matthew Barrett, Mark Whitcutt and Martin Lewis; all taken in early June. These show the features already described along with a small bright dot caught by Martin between the darker upper and lower presentations of the SEB, just prograde of the GRS. Martin and I tried to image this spot in the methane band but with no success.
Finally I will mention the visual reports of the Transit of Mercury as seen by Alan Heath and sent to me at the start of this period. He made very clear observations and I was interested to read that he was unable to see any distinct ‘black-droplet’ effect as the planet moved fully onto the face of the Sun. I will add his images to the SPA website in due course.