December 2015 and January 2016
I would like to thank all the section members who ventured out in the dreadful winter weather to make reports to the section. I cannot pretend that conditions have been anything but atrocious with reports of flooding and wind-damage to observatories and other buildings accompanying the flow of planetary observations. All I can say is let’s hope for better weather to come.
Most of the planets on view required a very early start to observe them but Uranus was available to the early evening viewer for much of the period and Dave Finnigan, the Deep-Sky Section Director, took advantage of a clear evening on the 11th of December to image the planet using his twelve-inch (305 mm) Meade Schmidt-Cassegrain telescope and two versions, mono and colour, of the ASI120 planetary camera. With this target, colour cameras don’t tend to capture illusive cloud systems moving in the upper atmosphere; these are more readily seen in the near infra-red frequencies. Dave used a colour camera to capture the overall colour-tone on view and then an infra-red pass filter on the monochrome camera to try and capture cloud detail.
I must say this is difficult work for the amateur and really positive results are only obtained under excellent seeing conditions. By combining the images taken with his two cameras Dave has managed to capture some subtle shading and a hint of atmospheric banding and must be commended for his efforts. The same techniques will also work well on Neptune when it next becomes readily observable.
Dave also observed the early-morning targets on view, specifically Venus, and his image from the 9th of December can be compared with a similar view taken by Carl Bowron on the 4th. While Carl used a colour camera fitted with a deep-blue filter (Wratten W47), Dave used a Baader ‘U’ Venus filter on his monochrome camera and both were attempting to capture some of the faint ultra-violet shading occasionally visible on the planet. This is another occasion when good, steady, seeing is really required as the UV end of the spectrum is particularly susceptible to atmospheric dispersion and refraction through turbulent air.
Some slight shading is visible in the monochrome image and these cameras are often more sensitive to short wavelength UV light than the colour versions. Despite having to image through the turbulent air of a Jetstream over-head, Carl’s image is sharper but somewhat less detailed, presenting an excellent representation of the view seen by a visual observer. Users of the W47 filter may like to note that while appearing deep-blue it actually ‘leaks’ a lot of invisible Infra-Red light so should be paired with an IR-cut filter for photographic work.
While discussing Venus I must mention an observation sent in by Philip Denyer in which he reports seeing shadows cast by the planet Venus from a very dark site used for the Breckland Astro Star Party. He wrote “I believe there has been in the past, accounts of Venus casting a shadow given a dark enough location. This phenomenon seemed very apparent recently to myself when I was at a site in Suffolk, and I feel the need to obtain a further opinion on the matter to confirm if this was indeed the case.” Sir Patrick Moore used to declare that only three celestial bodies were bright enough to cast shadows on Earth being the Sun, the Moon and Venus and I note that the well-known astro-photographer Pete Lawrence did an experiment on Selsey Beach back in 2005 (I think!) when he photographed the shadow cast by his hand on white paper. He suggested that the shadow is so faint that movement makes it imperceptible but that the shadow cast by a still object can be discerned if you are watching for it. I think young eyes and dark adapted eyes would have an advantage but Phillip’s report of a faint shadow cast by his hand on both a white table-top and a silver car seems perfectly credible. Who else has seen this phenomenon?
Moving on, Dave Finnigan also used his mono-camera on Jupiter on the morning of December 9th, this time fitted with an Astronomik IR-pass filter, specifically to try and counter atmospheric refraction effects by capturing longer wavelengths of light. His image shows a distinct bifurcation of the South Equatorial Belt (SEB) at these wavelengths with large festoon in the Equatorial Zone (EZ) and a relatively placid north Equatorial Belt (NEB). Shortly after this a number of amateur and professional observers commented on a thickening of the NEB over approximately 50% of its circumference with large disturbances seen within the belt. A series of images taken by Silvia Kowollik bears this out.
Imaging over three nights, the 27th to the 29th of December, Silvia used the free software WinJupos to compile a surface map of Jupiter over that period which shows some interesting features. The Great Red Spot is very obvious, sitting in its ‘eye socket’ within the southern edge of the SEB. Also obvious is the thickening of the NEB along both the left-hand quarter and right-hand third of the map (highlighted in the image) and a very obvious storm feature, White Spot Zulu (WSZ), cutting into the northern edge of the NEB. The expansion of the NEB northwards into the adjacent North Tropical Zone (NTrZ) appears to have originated from the disturbance caused by WSZ although there are a number of distinct small brown spots in the NTrZ that have, in the past, been associated with expansions of the NEB; one of these is noticeably redder than the others and has been christened elsewhere as the “North Red Spot”. One final feature of note from this map is the difficulty in picking out the once-prominent feature Oval BA. This seems to have faded considerably and no longer rivals the GRS in colour.
Matthew Barrett sent in two visual observations of Jupiter, from the 21st of December and the 16th of January, which shows the thickening of the NEB and the disturbed nature of that belt, including several dark concentrations contained within it. Steve Norrie imaged Jupiter in the early hours of January the first (now that is dedication for you!). The GRS is just starting to rotate onto the disc so the view shows the thinnest region of the NEB. It clearly captures the bifurcation in the SEB and large EZ festoons trailing into a patchy grey Equatorial Belt (EB). Further images were taken by Steve just after midnight on the mornings of the 15th and 16th of January showing similar features and, on the 15th, he caught the shadow transit of Io which was just evident on the NEB. Io was also on the disc at that time but was not quite resolved. Oval BA should also have been visible in that image but, once again, could not be made out with the Jetstream overhead causing poor seeing in our local Scottish atmosphere.
Steve also imaged Jupiter in the late evening of the 22nd and early morning of the 23rd of January. He used a monochrome camera and an IR-pass filter to combine with green and blue filtered images; the IR-pass filter provides a view somewhat less disturbed by poor seeing than visual wavelengths and replaces the red element of a normal RGB image. The technique shows slightly more detail than a simple RGB image, made from combining red, green and blue filtered images, if the seeing is poor. The GRS is just appearing over the limb of the planet and the thickening of the NEB can be seen to have advanced prograde of the GRS when compared with Sylvia’s map of late December.
Living close to Steve I have also suffered from poor seeing but was able to extract a reasonable image on the 23rd of January by capturing a simply huge number of images. I upgraded my laptop in the Christmas sales to one with a USB3 port by which my particular camera was able to pass video to the hard-drive at a ferocious pace; 22,000 images over a period of four minutes. Even with poor seeing the AutoStakert software was then able to extract, if not quite “a silk purse”, at least something worth looking at from the “sow’s ear” of poor seeing. The GRS is clear, as is the turbulent area within the SEB that extends retrograde from the GRS around half the visible hemisphere. WSZ is also obvious, near the central meridian in this image. The general view is that the NEB is expected to continue to thicken over the next few months and this area should be observed carefully as we move towards planetary opposition in the middle of the next reporting period. Thanks once again to the section members for their contributions and I’m looking forward to seeing your results in the next period.
Erratum. Please note that in the January and February edition of Popular Astronomy, the image showing the narrow conjunction of Jupiter, Venus and Mars was incorrectly attributed to Simon Kidd when it was printed in the ‘Showcase’ section. It should have been attributed to Paul Crossland as correctly mentioned in the October and November section report contained within the magazine and eleswhere on this website.