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Section Report for April and May 2017

 With Jupiter dominating the evening sky it is not surprising that the vast majority of observations in this period covered this fascinating and dynamic planet, however I am going to begin with Mars as I received probably the last observation of the current apparition on the 7th of April. Some ten and a half months after opposition with Mars a tiny 4.1 arcseconds in apparent size, Martin Lewis caught a remarkably good image of the red planet. The Elysium area is on the central meridian (CM) with half of Syrtis Major and the dark finger of Mare Cimmerium clearly visible. At this Martian season large dust storms have been recorded in the past, obscuring surface detail; from Martin’s observation it is clear that this has not yet happened. His image was taken with a large Dobsonian telescope and a one-shot-colour (OSC) camera through an atmospheric dispersion corrector (ADC) to combat the effects of Mars being low in the sky. I think it will be some time before the next Mars observation is reported.

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Venus also received some attention. I am glad Robert Steele was able to get in contact with me again so I can mention his attempts to view the controversial Ashen Light on the unilluminated phase of the planet.  This phenomenon is said to be a dull glow visible under the Venusian clouds and was first reported in 1643 by Italian astronomer Giovanni Battista Riccioli. Since then a number of well -regarded observers have reported seeing it but it has never been photographed. Robert observed Venus on 11 dates running up to inferior conjunction, as the dark phase of the planet grew, using a refractor and a high-quality eyepiece fitted with an occulting bar. This bar can be placed over the dazzlingly bright phase of the planet thus making any glow within the unilluminated part more obvious. Robert’s work was careful and meticulous and gave results which were, in his own words, “…entirely negative, with not even a suspicion of night-side illumination on any occasion.” It is possible that only people who have an ability to see certain frequencies of light can catch this phenomenon but without more reliable reports and, particularly, without photographic evidence support for the existence of the Ashen Light is becoming more difficult.
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Carl Bowron sent in a series of Venus images showing the changing shape of the bright phase. Of note, Carl took his images in full daylight allowing them to be made at higher altitude than is possible in morning twilight, thus reducing the amount of our atmosphere he had to peer through. His first observation from the 6th of April shows a tiny sliver of illuminated phase, just 5.6% full; no Ashen Light shows on the dark side.  The phase has grown to 45% by his last observation on the 26th of May.
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There was a single observation of Saturn in the period, made by Larry Todd on the 5th of May. I know many people have been put-off by the low altitude of this target but his image shows what can be achieved, showing an almost-complete Cassini division in the rings and subtle banding across the planet. The rings are open to us at nearly their maximum extent and are clearly visible above and behind the North Pole.
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But now I must move on to Jupiter, a lot has been going on within the atmosphere of this gas giant and has been observed assiduously by the section; I will summarise the observations so far. In the North Polar Regions of the planet a large grey oval storm has persisted at a longitude closely mirroring that of the Great Red Spot (GRS) but nearly opposite in latitude. This storm has remained obvious and been joined by a number of smaller but otherwise similar ovals spread around the same latitude in a region which is most often fairly uniform and undisturbed. Slightly further south the North Temperate Belt (NTB) has both darkened and grown following its outbreak at the start of this apparition. In this reporting period it developed both a thin vivid-orange southern element and a dark-grey northern element, being referred to as the NTB(S) and the NTB(N) respectively.
The North Tropical Zone is very thin and looks in danger of being swallowed by the North Equatorial Belt (NEB) which has expanded northwards in places and contains various pale diagonal rifts over some 50% of its circumference; these rifts also expanding visibly in the period with the whole NEB appearing unusually disturbed. Its northern edge contains a number of small white storms competing with White Spot Zulu (WSZ) which remains very visible.
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The Equatorial Zone (EZ) contains many obvious dark festoons ‘though there is no evidence of these joining into an Equatorial Belt as happened last apparition. The roots of these festoons, within the southern boundary of the NEB are very dark and obvious.
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The pale outbreak within the South Equatorial belt, reported on in the last period, has expanded and lengthened considerably giving this belt a bifurcated appearance prograde of the GRS. The same has happened retrograde of the GRS where the disturbed area within the SEB that trails the passage of the spot has grown considerably and is now notably long and of added complexity. The GRS itself has been resolved in great detail by the section (see below) but contains a darker red outer annulus, a pale orange inner and a dark concentration at its centre.  Two observers, Simon Kidd and Richard Bosman have caught a chain of pale disturbances rotating within the outer annulus, right at the limits of resolution.
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 The South Tropical Zone (STrZ) is broad and largely undisturbed. Rotating within it, now well prograde of the GRS sits Oval BA; pale orange and not obvious it is followed by a small tail of dark spots that may be an indication of an outbreak of the South Temperate Belt. The southern edge of the South Polar Region is now defined by a dark band containing some small dog-toothed protrusions into the STrZ, below which lie a chain of bright white oval storms ringed around the planetary circumference. These storms, along with the NPR storm, the GRS and Oval BA are very obvious in methane band images taken by the section.
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With a large number of Jupiter observations submitted I cannot cover each one individually in the space available however  there were clusters of observations that matched periods of better than average seeing around the end of the first week in April, the 22nd and 23rd of that month, the 5th to the 10th of May and from the 24th onwards.  Important contributions were received from Carl Bowron, Dave Finnigan, Dave Tyler, Martin Lewis, Steve Norrie (the most prolific contributor), Larry Todd and Alexei Price. Richard Bosman and Simon Kidd contributed particularly high resolution images capturing the concentrations within the outer annulus of the GRS. Mike Hezzlewood sent in a series of excellent sketches covering all clear nights at his location and he noted the 10th of April and the 24th of May as being the best of the apparition so far with the 24th being a particularly rare night, in terms of steady seeing. This last coincided with the night Simon Kidd was able to take his sharpest image of the GRS.
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I must mention a series of observations made by Tony Hayes from Dundee in Scotland in which he observed Jupiter through various binoculars in an attempt to resolve and note the positions of the Galilean moons; part of an observing challenge for the Dundee Astronomical Society. He used variously Helios 10 by 50s, Strathspey 12 by 50s and Revelation 15 by 70s over a series of nights, later adding Nikon 10 by 50s to the test. In the early tests, as one might expect, the larger binoculars were able to resolve the moons most often and provided hints of the dark belts on the planet. Once the Nikons were added to the test they eventually proved able to match or exceed the capabilities of the Revelations resolving all four moons and being brighter to the eye. It would be interesting to see how smaller image-stabilised glasses perform in this kind of test.
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Finally I report that on the 25th of May two European amateurs recorded the bright flash of an object impacting and burning up in the atmosphere of Jupiter. This is the fifth such impact discovered by amateurs and follows the events of 1994 when fragments of comet Shoemaker-Levy 9 died so spectacularly at Jupiter. It seems no UK amateurs observed this latest event but it is important to review any video files captured for these impacts, not simply stack the results to get a final image, as the short duration flash is then lost. Please do let me know if you discover anything!
Alan Clitherow.