June and July 2015
While the spring reporting period produced some good weather, allowing many observations, unfortunately this was not true of the early summer period which was rather less kind to us. Combine this with the lack of darkness and of well-placed planets and the result was a relatively small number of observations within the period, however valuable work was done by the section membership, particularly on Saturn and Venus and also, to a lesser extent, on Jupiter.
Jupiter declined into the western evening sky in the period and became hard to observe unless you were prepared to use specialist filters and to start observing in daylight. Dave Finnigan, Director of the Deep Sky Section, was able to take an image on the 9th of June using a monochrome camera and an infra-red pass filter to help cut through some of the low-altitude turbulence present in our own atmosphere. Poor seeing conditions when viewing objects low to the horizon can be very frustrating but Dave managed to capture a fair amount of detail showing that the South Equatorial Belt (SEB) of Jupiter is split by a long pale zone and that the Equatorial Zone is chaotic with large festoons streaming into it from a rather indistinct southern edge of the North Equatorial belt; the North Temperate Belt (NTB) does not seem to be visible at all.
On the 11th of June Martin Lewis managed to take a colour image of the opposite hemisphere which shows a more ‘normal’ face of Jupiter, proving that the split in the SEB does not extend around the planet and that at least part of the NTB exists, apparently as an outbreak from a small dark feature. Martin Used a pre-production version of a new camera by ZWO, called the ASI224MC. If you are familiar with ASI cameras you will know this designation means the camera is a one-shot colour (OSC) device but this one seems to be particularly sensitive outside the normal range of our vision. Indeed, Martin proved this by using it to take another image with a methane band filter, centred on 889Nm frequency, in the near infra-red. This is a remarkable result for a colour camera and this new model will certainly bear watching. Carl Bowron also managed to image Jupiter on the 30th of June, very late in the season, showing the same face as seen by Martin on the 11th. His was the last Jupiter observation I received for this current apparition and it will be interesting to see who gets the first of the next apparition in the autumn.
Accompanying Jupiter in the evening sky was Venus; reaching its point of greatest eastern elongation on the 6th of June when it was some 45 degrees east of the Sun at sunset. It too was sinking lower in the sky each evening but was sufficiently well placed for the section to make a number of excellent observations. Martin Lewis started things off with both ultra-violet and infra-red filtered images on the 3rd of June showing some subtle cloud features in the UV and a bland face in IR. What is very noticeable is the difference in phase shape between the two images with the terminator being more obviously concave in UV light than in IR light. This nicely demonstrates the difficulty in determining the exact point of 50% phase (dichotomy) that was due to occur 3 days later. Known as the ‘Schroeter effect’, after the lunar and planetary observer Johann Schroeter who first described it, the effect is due to the scattering of reflected sunlight within the thick atmosphere of Venus, a scattering that effects blue light more than red. The result is that different individuals with differing sensitivity to light colours will see dichotomy at different times.
Leo Aerts also sent in some excellent UV images of Venus. He uses a rather unusual telescope, being an old but beautifully made classical Cassegrain telescope, of 250mm aperture and 7.5 metres focal length (F30). Such a telescope requires a very accurately made parabolic-section primary mirror and an even more accurate hyperbolic-section secondary to produce aberration free results but if well made, as in this case, the result is a near perfect planetary telescope. I do not know of any commercially made telescopes of this design being produced for the mass market, perhaps due to the careful production and matching of mirrors required, but the results do speak for themselves. Leo’s image from the 3rd of June, using a UV Schuler filter, has caught cloud detail with twin patches of lighter material towards the poles (often referred to as the ‘cusps’ when Venus shows a marked phase) and one extending from the limb towards the terminator. These bright patches are often observed near the poles, which receive less sunlight than any other directly lit portion of the planet, and their presence remains largely unexplained. There is a suggestion that reflective aerosols are forming at high altitudes which then obscures the lower material whose absorption of methane-light causes the dark patches we see through these filters. Exactly what comprises the aerosols or what absorbs the light is unknown.
On the 4th of June Dave Eagle also caught some UV detail with a 190mm Makzutov-Newtonian and the polar-region patches of light are still visible if less distinct; by the 11th of June Martin Lewis’s UV image shows a general fading in UV detail, something I noted myself, with little distinct to see for the rest of the reporting period. Another set of UV and IR images from Martin on the 29th shows the reducing visible phase following on from dichotomy; this is also obvious in very smooth white-light images taken by Carl Bowron on the 30th of June and the 5th of July, these being captured after some essential surgery to his Celestron GEM which had electronic problems earlier in June. Venus observations were completed by another IR image from Martin on the 7th of July and a final white-light image from Carl on the 15th, taken in broad daylight while Venus was still high in the sky. Venus will move into inferior conjunction, between the Earth and the Sun on August 15th and it will be possible for suitably equipped amateurs to follow it in daylight right up to that date; as long as suitable precautions are taken to avoid pointing the telescope directly at the Sun. Daylight observation that close to the Sun is best done by camera rather than optically because of the obvious dangers.
As noted earlier, Jupiter and Venus spent much of the period in close proximity and between the 30th of June and the 1st of July they came very close together indeed; less than half a degree apart. This presented an opportunity for some wider than normal views of the planet with Jupiter and Venus of similar sizes and separated by just the width of the Moon. Indeed Simon Kidd took an image showing the two planets and composited it with an image of the Moon at the correct scale to show just how close the pair came. Martin Lewis also caught the pairing, as did Paul Brierley and Sally Russel. Getting an exact exposure was difficult because the high brightness range between Venus at magnitude-4.4 and Jupiter at -1.8 but the results were excellent, especially Sally’s with the planets caught in a gap between foreground clouds.
Finally we come to Saturn. This has been a hard planet to observe in great detail from the UK because of its low elevation; observers in the south had a slightly better time of things than I did in Scotland and southern-European and equatorial observers were able to get excellent views of the wide-open ring system with the planet high in the sky. Nonetheless UK observers did well, some using specialist tools such as Atmospheric Dispersion Correctors to correct for the rainbow patterns of refracted light that surround bright night-time objects viewed low in the sky. Of course steady air was still needed to get real detail but when our atmosphere obliged, the results were impressive. Sadly no amount of astronomical equipment can compensate for the roof of my neighbour’s house which nicely obscured Saturn for much of the period!
Both Martin Lewis and Dave Finnigan took images on the 3rd of June, in a patch of unexpectedly good seeing. Martin’s image is exceptional, benefiting from both the steady seeing and expert use of an ADC. It shows the planet’s southern Polar Regions peeking through the dark gap of the Cassini Division within the rings, a hint of the Enke Division, the shadow of the Crepe Ring on the planet and multiple surface banding with distinct points to the hexagon-shaped dark cloud formation surrounding the north pole. More southerly observers had found a dark spot at 64.1 degrees north latitude around this time but, unfortunately, the S3 longitude of this spot was right on the limb at the time of Martins image so wasn’t visible. Dave’s image was taken slightly earlier than Martin’s but shows, essentially, the same features and colouration. Dave also sent in a wide-angle view of Saturn taken on the 7th in which he composites a well-exposed Saturn into a longer exposure showing no less than seven moons surrounding it; a most interesting image.
Paul Crossland also managed to capture Saturn on the 7th of June, with a OSC camera, and brought out the pale green-yellow colouration of the methane-rich cloud tops, then Dave added another image on the 9th with a clear Cassini Division and surface banding, however that completed observations in June as a period of poor weather shook the UK. Things picked up in July with Martin adding images on the 6th and the 9th using his new ASI224MC camera and comparing the images from this OSC camera with similar ones taken at the same time through a more expensive monochrome ASI174MM, used to make an RGB composite. It must be said that the new, cheaper, camera loses nothing in detail to the monochrome camera in this set of images.
Paul Crossland added a total on 18 images taken on the 7th of July, showing good colour and a hint of the Crepe Ring. Because the rings are so open at the moment it is possible, in the sharper images, to see over the North Pole and to catch a hint of the edge of the ring system behind the planet. Something similar is visible in images from Dave Finnigan on the 15th and Simon Kidd on the 19th with Dave reporting that a neighbour’s tree stopped him from taking more images just as the air started to settle down (“Leylandii stops play!”) and Simon reporting that a hailstorm damaged his observatory shortly after an aircraft flew right through the middle of his image, adding wake vortices and contrails to the unsteady atmosphere. It is amazing that he managed to get an image at all from the resulting video file but, as he said himself, “What amazing software we now have at our disposal”.
A “looking Ahead” article can now be found on the PopAstro website if you would like ideas on what to observe in the next reporting period. A big thank you to contributors for the current period and wishing you all clear skies.