Section Report for Dec'16 and Jan'17
Most observations in this period were of Venus, however there were some significant developments seen on Jupiter, a lack of developments seen on Mars and a “Farwell” said to Uranus; the section has been busy!
Throughout December into January Venus became more obvious in our western evening skies and the planet reached its greatest eastern (evening) elongation from the Sun on the 12th of January; separated from the Sun by 47 degrees. In theory the planet should have presented a 50% illuminated phase on that date however eastern elongations often see 50% phase being reached observationally a few days earlier than the predicted date (and a few days late on western, morning, elongations) and this proved to be the case this time. Alan Heath, an extremely experienced and well respected visual observer, sent in nine observations from the 14th of December to the 2nd of January, recording and any visual cloud patterns on show along with the visible phase.
Venusian cloud patterns are of very low contrast and not everyone can see them as this requires some sensitivity into ultraviolet wavelengths. Alan reports only “suspected” markings except for the 27th of December when he felt confidant of a faint vertical streak seen with a yellow filter. It is very interesting to compare his drawing with an image taken by Martin Lewis at almost exactly the same time. Although not identical there is a strong correlation which, to me, confirms the accuracy of Alan’s observations.
Carl Bowron submitted images from late December and up to the 14th of January. Taken with a colour camera these record perfectly the visible phase and confirm the impression that dichotomy (50%phase) occurred before the 12th. Other observers made images using either ultraviolet or infrared filters and captured dark clouds in ultraviolet light; Steve Norrie’s infrared images catch the phase precisely while Dave Finnigan’s images from the fourth and fifth of January showed how notably the ultraviolet cloud detail changed over a 24 hour period.
Venus has a normal orbital motion but rotates strangely on its own axis; its ‘day’ is extremely long, slightly longer than its ‘year’, and its daily rotation is in the opposite direction to almost all the other planets, with only Uranus sharing this odd retrograde direction of daily rotation. The atmosphere also follows a retrograde path but its own rotation around the planet is very rapid, ‘super-rotating’ around Venus in only 4 to 5 Earth days. Venus is famous for massive ‘V’, ‘Y’ and ‘Ψ’ shaped clouds with the base of these symbols lying along the equator. For eastern elongations these markings appear at the limb and rotate towards the terminator. None of these particular formations were seen very clearly by the section but Martin Lewis captured outstanding detail late in January revealing the subtleties of what is on show there in the ultraviolet.
Mars has been sitting close to Venus through this period. It is actually higher in the sky and observable for longer than Venus but its great distance makes for a tiny target and detailed observation is difficult, requiring excellent seeing conditions. The season on Mars is late high-summer for the southern hemisphere and the much-shrunken South Pole has been tilted slightly towards us. The planetocentric longitude of the Sun as seen from Mars is a good measure of the season there and in mid-January it reached 300 degrees, where 0 degrees signals the transition from Summer to Autumn for the southern hemisphere. In the past this time has seen the triggering of large, even planet encircling, dust storms with all major surface features disappearing or becoming very faint under a uniform yellow-orange pall of dust. Despite the small size of Mars visually it is important to monitor the planet to look for the start of these events.
Simon Kidd and Martin Lewis sent in excellent images through December with the southern ice-cap clearly visible and enough detail on view to establish that no major dust events were under way. Simon’s image from the 4th of December shows an 88% illuminated globe with Sinus Sabaeus on the central meridian (CM) while Martins view from the 18th has Elysium on the CM; his image of the 27th matches that made by Simon a day later, having Nix Olympica placed centrally on the disc. Absolute detail is difficult to see on such a tiny target, around 6 arc-seconds in diameter and shrinking through the period, but enough can be observed to say that no major dust events started in December.
The story continues in January with my own observations from the 17th and 29th of the month and those from Martin on the 18th, 20th and 22nd. His image from the 18th is particularly note-worthy with Syrtis major and the Hellas basin on the CM and with a dark band visible around the shrunken south polar ice-cap. Mars is observable until at least early May this year and I would welcome continued observations of the weather there by the section members.
Which brings us to the weather on Jupiter; there have been two notable events since Jupiter returned to the early morning skies at the start of its latest apparition. First of all it was noted that there had been an outbreak of considerable activity in the northern hemisphere with dark encircling bands appearing north of the North Equatorial belt (NEB) and continuing all the way up to the polar regions; an area that had been more uniformly pale at the end of the last apparition. Then, an Australian observer, Phil Miles, caught a large plume of white material rising within the South Equatorial Belt (SEB) at around L2 longitude 208 degrees, first seen at the end of December. These plumes have been noted on several previous apparitions and usually multiply and grow from small white oval storms, with banners of light material being torn away from them by the jetstreams within the belt. They can last from several weeks into months and will be an obvious target for the JUNO probe currently studying the atmosphere of Jupiter.
Steve Norrie has caught precisely this region just off the CM in his image from the early hours of the first of January (now, that’s dedication for you) with an extended bar of lighter material within the SEB visible in both visible light and infrared based images. His pictures also show the general darkening of the northern hemisphere. Dave Finnigan also caught the region close to the CM on the 20th of January with his infrared image showing an expanding bar in the right location. His methane band image taken some 15 minutes later fails to show anything clearly, which is interesting as these should be high points in the atmosphere and visible in reflected light around the methane absorption band. Simon Kidd took a superb colour image on the same morning, just slightly before Dave, and this resolves the white bar into two obvious tadpole shaped features, the heads of which are erupting white oval storms within the SEB and the tails are clearly shown blowing away on the jet stream as the tadpoles appear to swim across the face of Jupiter.
More observation and reporting of this area are essential. Freeware programs such as Winjupos can be used to predict just when the correct region will be visible on the disc. Steve Norrie also added images on the 26th of January showing the Great Red Spot rotating off the disc and the massive turbulence area that follows it around the planet.
Saturn has been barely visible, very low in the morning sky, and was not observed in the period. On the other hand Uranus has been sitting even higher than Venus and Mars in the early evening sky however excellent seeing conditions are needed to make anything out; I didn’t have any! I tried several imaging-runs however even the best of them, taken on the 19th of December, revealed no banding or subtle detail on this distant ice-giant. Dave Finnigan had more luck on the 14th of December with some faint banding and other contrast features, while Martin Lewis had a very clear result on the 29th showing the lighter region around the north polar area, faint equatorial banding and a bevy of orbiting Moons; Miranda, Ariel, Umbriel, Oberon and Titania. It is, however, unlikely that the section will observe the distant outer planets again until the summer and autumn when both Uranus and Neptune will be, once again, well placed for observation.
Thanks to all for your continued and valuable contributions to the section and wishing you clear and steady skies in the next reporting period.
As an addendum I must include this outstanding montage of all seven major planets as imaged by Martin lewis during 2016.