Popular Astronomy

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December 2014 and January 2015

 The section received a large number of excellent observations through this reporting period. Not surprisingly the vast majority dealt with Jupiter which was riding high in the southern sky throughout, offering ample opportunity for detailed observation when steady seeing prevailed; although there was not as much of this as most observers would have liked! Rather than give a chronology of the Jupiter reports I shall, Instead, detail the features noticed within the images by section members starting in the northern regions of Jupiter and working south. Just to make things complicated please note that images are, as usual, printed with south at the top so we are working bottom-up through the pictures.

Just below the North Polar Region the North-North Temperate Belt (NNTB) was continuous and placid with few disturbances but the normally more prominent North Temperate Belt (NTB) only existed as fragmentary long-dark features, clearly seen in images from Dave Finnigan on the 16th of January and by Mike Andrews on the same night. Images taken by Steve Norrie on the 8th and 13th of December show that this belt was missing over most of the circumference but Mathew Barrett recorded small dark features visually on the 29th of December and Paul Crossland tracked a dark feature there on the 7th of January so a low-level outbreak of this belt maybe underway.

Moving in to the North Tropical Zone, and a possible darkening of a large anti-cyclonic storm known as White Spot Zulu (WSZ), was seen within that zone. This was also reported during the last apparition when WSZ was seen to turn pink for a brief period but soon returned to its normal white or pale-yellow colouration. Images sent by Steve Norrie on the 27th of December show WSZ as a small colourless indentation in the northern edge of the North Equatorial Belt (NEB) but the same area in his images of 17th January show a reddening of the storm making it quite prominent in both infra-red and red light. My own images of 24th January tend to confirm this making WSZ an area of interest for future observation.
The NEB belt was slightly thinner than its southern counterpart but was continuous with large and very dark barges on its southern edge, recorded well by Steve Norrie on the 6th of December and Paul Crossland on the 7th of January. Large and very long festoons were noticeable stretching from the NEB into the Equatorial Zone (EZ), particularly in a sequence of images taken by Mike Andrews on December 31st. It seems that these extended festoons may be responsible, at least in part, for a faint, dark, Equatorial Band (EB). Steve Norrie’s image from 27th December shows this well using IR light in place of red but Paul Crossland’s images on the 13th and 30th of December also show a patchy EB using a one-shot-colour camera. This band is absent in images taken with the Great Red Spot (GRS) near the Central Meridian of Jupiter suggesting that it is confined to perhaps only 50% of the equatorial circumference.
The South Equatorial Belt (SEB) was generally the thickest and most noticeable feature on Jupiter with disturbances some 40 degrees prograde of the GRS (perhaps being the remnants of the ‘banner’ feature reported in the spring of 2014) and with an obvious thickening and protrusion into the pale South Tropical Zone (STrZ) just retrograde of the GRS; this is very clear in RGB images taken by Mike Andrews on December 14th but had disappeared by the 16th of January. A stiletto-like dark belt can be seen extending prograde of the GRS itself and later images show this belt extending further around the planet. In Mike’s image the GRS is surrounded by dark material and is separated from the SEB itself by a narrow area of pale yellow material making the spot appear larger than it actually is. Images from late November had shown the GRS almost “popping-out” of the SEB with a pale white band separating the two. By the end of the reporting period this pale band was back, very obvious in Dave Finnigan’s image of 16th January and Robin Scagell’s of the 18th, reducing the apparent size of the GRS which has a darker annulus surrounding it; the GRS is currently light-orange rather than red and has a small dark concentration at its centre. Note that images using IR light instead of red light still show the GRS as brick-red but this is a result of its high level of reflectiveness at these frequencies rather than a true representation of how it appears at the eyepiece.
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To the south of Jupiter the South Temperate Belt (STB) is disturbed and split as it passes around Oval BA (aka ‘the little red spot’) which is itself pale-pink but with a dark annulus surrounding it making it relatively easy to find. The northern half of the STB extends prograde around most of the planet, fading out over the last 90 degrees or so as it approached the disturbed area just south and retrograde of the GRS; the southern half fades out as it merges with a slight thickening of the dark belts surrounding the South Polar Region (SPR). Orbiting in the northern edges of this region are at least 9 white-oval storms, two of which collided just to the south of Oval BA during the reporting period but I am unsure, as yet, what the outcome of this interaction will be.
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Having scanned north to south across Jupiter we must now consider the series of mutual-events occurring between Jupiter’s main four ‘Galilean’ moons. In the period we were observing the orbit of these moons edge-on such that they all appear to transit Jupiter in a narrow belt contained within the EZ with the shadows cast by these moons contained within the same area. This means the moons will, on occasion, pass directly in front of one another, known as an occultation, or have their shadows fall on each other, known as an eclipse. It can be fascinating to watch these moons merge or fade out and re-appear over a period of just a few minutes and a list of mutual events is published under the planetary News section of the SPA website; mutual events continue well into spring.
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On the 13th of December Simon Kidd imaged the merger of Io and Europa and these two moons, because they occupy the closest two orbits to Jupiter of the Galilean moons, appear to interact most often in the sequence of events. Steve Norrie caught Io and Europa in transit across the face of Jupiter on the 26th of December with Ice-covered Europa being particularly bright in reflected IR light, thus appearing as a red spotlight in his image.
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On the morning of January 24th the last in a series of three triple-shadow transit events occurred in which the dark shadows of three moons could be seen at the same time on the face of Jupiter. This event will not happen again until 2032 so a number of members did their best to capture it. The problem was that the triple-transit occurred from around 0630 to 0650ut with Jupiter rather low in the western sky and, on the day, jet-stream activity over Britain made the seeing conditions very poor. Paul Crossland took an amazing sequence of images showing development of the transits from single to double shadows; his image at 0501ut has caught three moons, two shadows and WSZ as an added bonus. His last image from 0632 may have just caught the edge of the third shadow as it fell on Jupiter. I say ‘may’ because seeing was so poor at this stage that, perhaps, a degree of imagination is needed to see these shadows in the images; this is certainly true of my own image taken at 0640ut.
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Steve Norrie and Mike Brown had similar problems but Mike’s image at 0611ut captures Io in transit, just about to complete its merger with the shadow cast by Calisto and trailing its own shadow slightly within the EZ. Steve’s image of 0639ut also shows Io in transit with two definite and the hint of three shadows. Dale Holt made an excellent sketch at around 0550ut with Io approaching the CM and its shadow starting to merge with the shadow of Calisto; Calisto and Europa being just off the eastern limb. Excellent work there from section members and I thank them for making the effort.
Moving on to other observations, Uranus started the period well-placed but declined to the west markedly by the end of January and did not show any more signs of the large northern-hemispheric storms hinted at in the last reporting period. My own observations of December 3rd showed a bland and detail-less disc while Graham Taylor’s image of December 23rd, taken in the infra-red with the Bradford Robotic Telescope, revealed a bright north-pole region but no concentrations or other details that might be storm features. We will have to wait until the summer to get another detailed view of Uranus and to find out if the storms persist.
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Venus has started to become a prominent evening star; still quite low to the western horizon after sunset it will improve dramatically in the next reporting period and become an important target for observation. Over Christmas Tony Ireland took two atmospheric wide-field views of Venus, on both the 28th and 29th of December and John Fletcher added another from the 29th taken with a longer lens and showing a hint the planet’s phase. February and March offer excellent opportunities for viewing both Jupiter, with its continuing mutual-events between moons, and Venus as it becomes a dazzling beacon in the evening sky. Thank you to all section members for your contributions and I look forward to seeing your results for the next reporting period.
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Alan Clitherow.