Popular Astronomy

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February and march 2015

 This period was an extremely productive one for the section. In all I received over 200 separate visual or photographic observations and I must thank section members for their tremendous efforts. It is not possible for me to show images from every contributor, for which I apologise, but I will try to summarize the excellent work done during this period.

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Observations fall into 4 sections; observations of surface detail on Jupiter, observations of the mutual events between the four Galilean moons of Jupiter, views of the changing phase of Venus and finally early views of Saturn. I will work through these in strict order starting with the southern regions of Jupiter.

Carl Bowron started me off with observations of isolated white spots in the deep southern hemisphere on the first of February, followed by images taken by Martin Lewis on the same night. It was immediately clear that Oval BA was very pale and remained so throughout the period; it was only made obvious by a dark ring of material surrounding it. Slightly south of BA was a line of white oval storms moving prograde at perhaps 5 degrees of longitude in 15 days relative to Oval BA. Steve Norrie’s image from the 16th of February shows that one storm had moved past BA without disruption and another was approaching. Between them a pale patch of material was being disturbed by the pair, giving a distinct cluster of 3 storms just south of BA and reminiscent of the ‘Mickey Mouse’ face feature seen last apparition. By the 10th of March Carl’s image shows that the pale patch was gone and that the second storm had passed BA. In all 7 white oval storms were discernible in images taken in this period which is two less than last apparition.
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The South Tropical Zone (STrZ) started the period with a thin but distinct South Temperate Belt (STB) over much of its circumference but this had faded and broken into a few dark spots, over the hemisphere containing the Great Red Spot (GRS), by the end of the period.  A South-South Temperate belt (SSTB) existed up to Oval BA but was disrupted prograde of BA, merging into the STB to form a single dark band. Alan Heath’s visual observations of this region recorded that the STB, where it was visible, appeared to merge into the South Polar Region as a darker edge to that region, rather than a distinct band however the STB was clearer around the opposite side of the planet, as can be seen in Paul Crossland’s image from 21st of March.
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In the last reporting period there was a very prominent ‘stiletto’ shaped band seemingly attached to the GRS and moving prograde as a section of the STB, but this had disappeared by the 17th of February. The spot itself started the period with a dark annulus around it and this persisted to the end of March but became less distinct as time moved on. Several images showed a dark concentration at the core of the spot, particularly that of Mike Andrews (13th March) and Simon Kidd (22nd march). The spot appeared isolated, sitting within a distinct ‘socket’ within the South Equatorial Belt (SEB) which had, itself, a distinctly darker southern edge; most noticeable pro-grade of the GRS. Occasional colour shades were seen in the pale GRS socket, particularly on the 26th of February when Dave Finnigan imaged a yellow colouration in this pale zone.
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In mid-February images started to show a distinct white disturbance in the SEB just behind the socket containing the GRS. This evolved quickly and was very noticeable before breaking into at least three parts and then fading somewhat; but it was still clearly visible at the end of the period. Otherwise the SEB appeared to be relatively undisturbed with the afore mentioned dark southern edge and an almost linear edge forming its northern boundary with the Equatorial Zone (EZ). A faint Equatorial Band (EB) persisted from last period and it was clear from a number of images that this was an extension from large but relatively faint festoons dropping into the centre of the zone from dark areas on the southern edge of the North Equatorial Belt (NEB); these festoons were more obvious when infra-red light was used to replace red light within an image but were hard to see visually; neither Alan Heath nor Matthew Barrett were able to report seeing festoons in their visual observation forms. In any case both the festoons and the EB seemed to fade somewhat by the end of the period.
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In contrast with the SEB, the NEB was thinner and much more disturbed. A number of large barges were visible on its southern boundary and the northern boundary, with the North Tropical Zone (NTrZ), followed a distinct if irregular wave-form pattern. White Spot Zulu (WSZ) has, in the past, been difficult to spot but at least five section members caught it beautifully photographically and Mathew Barrett drew a curved indentation in the NEB at the right latitude to match up with this large and persistent storm feature. A white oval storm within a very pale zone is hard to pick out but WSZ has picked up a surrounding ring of slightly darker material which enhances its visibility; in IR light it has a distinct red shade making it stand out even further.
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 A strange ‘snake’ feature was visible in mid to late February as a dark belt which was diverted from the north side of the NTB to the south side, apparently caused by contact with the edge of WSZ. This distinct feature faded rapidly in early March. Apart from WSZ the  NTrZ itself is otherwise almost completely undisturbed with only pale and ghostly hints of a North Temperate Belt (NTB) and a thin, but distinct, dark boundary separating it from the North Polar Region (NPR). Both the extreme north and south of Jupiter seem relatively featureless with perhaps one small white spot in the south and some faint banding in the north.
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Jupiter was at opposition on the 6th of February and, because our line of sight currently sits edge on to the orbital path of the four Galilean moons, Io, Europa Ganymede and Callisto, any moon in transit across the face of Jupiter sat directly in line with the shadow it cast on the planets face on that date. In addition mutual events between the moons were relatively common where one moon moves in front of another, causing an occultation, or where the shadow of one falls on the face of another, causing an eclipse. A number of excellent moon and shadow transit images were received showing moon and shadow moving closer together and then slowly drawing further apart as the days moved on past opposition. One in particular caught my eye, taken by Martin Lewis on the 17th of February. Io and its shadow are caught moving across the EZ of Jupiter, separated by just a few seconds of arc. Most noticeably the image of Io has a bright equator and darker poles accurately matching what one would expect to see were one able to get much closer to the action. This is simply excellent resolution for an amateur image.
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As for the mutual events themselves, Mike Andrews managed two quite extraordinary results. On February 9th at 2100ut he caught Io moving across the face of Ganymede with Ganymede itself showing surface texture. Then, on March 2nd between 2022ut and 2028ut he caught the shadow of Ganymede crossing the face of Europa. At mid-eclipse Europa almost completely faded out against the background sky. I show images of these events both enlarged and contrast-inverted to make the action more obvious. These mutual events continue into the next reporting period and, with luck, we may hope for more such extraordinary observations. Details may be found on the SPA website within the news area of the planetary section.
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Now let us move a little closer to the Sun. Venus started the period as small and distant; a low and early-evening object with little visible phase. By the end of March things had improved considerably with apparent angular size noticeably increasing and a clear illuminated phase on view. Optically Venus can be very bland to view; its cloud tops appear largely featureless with, perhaps, a slightly dull sulphurous yellow hue.  There are visible cloud features on Venus caused by an unknown substance in the upper atmosphere that absorbs ultra-violet (UV) light. This produces slightly darkened bands and patches across the illuminated face of the disc. Sadly I am quite unable to see these myself as I lack sensitivity at the deep-blue end of the spectrum, as do many other people, but a few observers report seeing ‘V’ and ‘Y’ shaped darker patches pointing from the terminator to the bright limb. Photographically it is possible to capture these features.
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Section contributions show nicely the increasing size and decreasing phase of Venus during the reporting period with Brian Woosnam, Carl Bowron and Robin Scagell using colour cameras; Carl took images early in February close to midday, showing that daylight observation of the planets is practical and effective. Both Dave Finnigan and I used monochrome cameras and UV-pass filters, imaging in early twilight to increase the contrast of Venus against the background sky.  Dave’s images from the 3rd and the 7th of March both show low-contrast bands and a larger ‘>’ shaped feature. Mine, taken on the 20th also caught this shape but with much less contrast; Venus will improve noticeably in April and I hope to get clearer results with this method later on. For information Dave used a Baader UV pass filter and I used an equivalent one by Astrodon. Visual observers may like to try a deep-blue filter to see if they are sensitive to the appropriate frequencies; blue (Wratten 38A) and violet (Wratten 47) filters are recommended for this.
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Finally I must mention the images of Saturn sent in by Mike Andrews. These were obtained using a 685Nm infra-red pass filter on a monochrome camera during the pre-dawn hours of the 2nd of February and the 5th of March. The low elevation of Saturn from the UK is a problem this apparition. It means we view the ringed planet through a great thickness of our own atmosphere and this increases the chance of poor seeing conditions. Infra-red filters are less disturbed by poor atmospheric seeing so are a useful tool in trying to pick out detail in low-elevation targets like this. With the rings tilted towards us by nearly 25 degrees and the north-polar area clearly on view it is certainly worth the effort to see Saturn this apparition. Mike has caught nearly all the Cassini Division within the rings as well as cloud-top banding and a clear shadow, cast on the rings by the north pole of the planet and I thank him for making the effort.
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Before I sign off I must mention the Jupiter images sent in by Paul Brierley, taken with a DSLR camera. Paul used Canon1000D and Eos Movie Record software to capture video files of the planet. Virtual Dub software was used to convert the files to a format recognised by stacking software and the final result bares comparison with many of the images sent in to me. Other DSLR users may like to try this approach. While it is impossible to show images from everyone I must say thanks, in no particular order, to Paul Crossland, Michael Andrews, Martin Lewis, Matthew Barrett, Brian Woosnam, Carl Bowron, Dave Finnigan, Steve Norrie, Robin Scagell, Alan Heath, Mike brown, Paul Brierley and Simon Kidd for their excellent efforts.
Alan Clitherow