Popular Astronomy

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August and September 2014

 With the section reports being published in the Society magazine some 3 or more months after they were originally created it can be seen that they can be thought of as a little out-of-date. With that in mind I now intend to post them here first. The same report will appear in print at a later date but the Society website allows the efforts of the section membership to be seen soon after they were made and I hope this will meet with the approval of members.

 
August and September was not expected to be a bumper period for planetary observation with all the more obvious targets being poorly placed for observation and only distant Uranus and Neptune being relatively well up in the evening sky. With this in mind I was extremely pleased that section members managed to observe and image every major planet in the solar system with the single exception of Mars; this was a tremendous effort.
Mercury was on the far side of the Sun from Earth, at Superior Conjunction, on August 8th, and could hardly have been worse placed. Despite this Simon Kidd caught an image on the 21st of August showing 93% illuminated phase when the planet was just 12 degrees from the Sun. The image was taken in broad daylight at 1024ut using a monochrome camera and an infra-red pass filter; 742Nm upwards. Simon continued with a Venus image taken some 50 minutes later using a dark-blue filter in an attempt to show some detail in the upper-cloud structure of the planet; a challenging thing to attempt in daylight, more often tried in twilight conditions using filters that pass ultra-violet light. Daylight UV imaging of the sky is almost impossible due to scattering of light at this end of the spectrum so Simon is to be congratulated on capturing the 95% phase of the disc along with some subtle atmospheric shading.
Carl Bowron also tried this difficult task, imaging Venus in daylight on the 19th and the 31st of August, all around 0900ut. He tried white light imaging using a UV and IR cut filter and also a W47 violet filter on a Neximage-5 one-shot-colour (OSC) camera. Given that OSC cameras have reduced sensitivity outside the visual range of light frequencies the violet image was extremely faint but the white-light images give a similar result to Simon's work, showing phase and limb-darkening. It is very encouraging that section members are experimenting with daytime imaging but a word of warning is mandatory here. If you are going to try daytime observing or imaging ensure you fully protect yourself from accidental exposure to the Sun. When planets are this close to it, scanning around with binoculars or a telescope is a recipe for disaster; be warned! Peter Parish also observed Venus while on holiday in Spain, but with the Sun below the horizon. Venus was so close to the horizon he was able to see a reflected column of light in the sea below the rising planet. Peter gave a very evocative description of this phenomenon and described how it disappeared at the first touch of true daylight. 
I mentioned that no observations of Mars were received from within the reporting period; however Martin Lewis put in some excellent work, collating all his 2014 images into a map of albedo features. These maps are significant in that the visible surface features are not fixed and unchanging. The general outline alters subtly from apparition to apparition showing that Mars is a dynamic planet with active weather and erosion over time. Mars will not be properly placed for observation for some time, not reaching opposition again until 2016, so it will be fascinating to compare Martin's current map with later observations.
Moving on to Jupiter and we start with a close conjunction with Venus seen in the pre-dawn skies of the 18th of August. Mike Feist observed this and described Venus as “glittering diagonally above a pale Jovian disc”.  Peter Parish reported and photographed a wide field view of a similar scene on the 20th when the two planets were still closely placed. Having discussed the daytime observations of Venus it will not be surprising that similar efforts were made with Jupiter, given their proximity. Carl Bowron took mid-morning images on both the 19th and 31st of August using his OSC camera. These clearly capture the Great Red Spot along with major cloud belts and zones and shows that there have been no gross-detail changes in Jupiter while it passed behind the Sun; something that can't be taken for granted. With Jupiter slowly becoming more accessible as an early-morning object, Michael Andrews then contributed a series of images using his OSC ASI120MC camera and his C11 telescope; starting on the 9th of September and concluding on the 25th. While confirming the lack of major changes seen by Carl, Mike's image from the 14th of September shows very large festoon activity in the Equatorial Zone and gives hints that a thin Equatorial Band, a new narrow dark belt, may be forming over substantial parts of the EZ. These bands are quite rare and transitory; I would like to confirm this discovery using later images and, although there may be hints in an image take at 0311ut on the 26th of September, I cannot do so yet. Confirmation or otherwise will have to wait for the next reporting period. I will mention Saturn in passing. Michael Andrews managed to obtain a twilight image on the 3rd of August just after 2100ut when the planet was 17 degrees above the horizon. It shows all the major features and colourful atmospheric banding. Saturn is moving towards conjunction with the Sun on the 18th of November and is unlikely to be imaged again until well into the New Year.
So now we move into the outer solar system. Uranus was well placed throughout the period, moving towards opposition on the 7th of October when it will sit more than 30 degrees above the horizon for around 5 hours. The problem with Uranus is that it can be seen as rather unrewarding to observe. Firstly its distance from us means that it is always a small visual target. Secondly its cold atmosphere lacks obvious weather systems meaning it reveals a rather bland blue-green disc and little else. Some experienced observers with larger aperture telescopes have reported seeing low-contrast banding and zoning but I have never managed this with my own 10” Newtonian telescope. However over the last couple of years well-equipped and experienced imagers have had some success capturing these features using monochrome cameras and filters that pass deep-red and near infra-red frequencies, especially with large aperture telescopes.
Michael Andrews took images on the 20th and 24th of August that nicely show the slightly flattened blue green disc of the planet, moving through space with its highly inclined rotation-angle, North Pole tilted towards us. The image from the 24th has, at high magnification, some subtle contrast features that might be taken for equatorial banding. I am reluctant to confirm this feature simply because the shading is so subtle and might be an artifact from image processing, but neither can I be certain that the banding isn't there so Mike may have pulled off a very difficult feat. I tried to repeat this myself with no obvious success. 
On 28th of September I used a monochrome camera and a Baader 610Nm 'long-pass filter', that is one that passes light from 610 Nm frequency upwards well into the near infra-red, on a 10” Newtonian with a 2.5 times PowerMate Barlow lens, taking some 8000 frames and stacking the best 1000. The result is even less clear-cut than Mike's. Comparing them with an image taken by the well-known European amateur Marc Del Croix on the 28th of August using the same filter but on a 320mm aperture Newtonian, it seems that larger aperture is the secret to catching these difficult infra-red features. Dave Finnigan also used his 305mm LX200 telescope on Uranus with a OSC camera and a UV/IR cut filter. This produced, for me, a very accurate rendering of what can be seen at the eyepiece with a good telescope but will need some element of the IR frequency-band to capture the detail seen by Marc Del Croix. I am concentrating on this because, in August, professional observers using infra-red frequencies caught images of enormous storm features in the northern latitudes of Uranus. In theory these features are within the reach of well-equipped amateurs and I would really like an SPA member to be one of the first to do so.
Finally, on the 17th of August, Michael Andrews managed to capture an image of distant Neptune. The tiny blue disc of this 'ice-giant' planet is clearly visible despite being just 2.3 seconds of arc across. In a period not over endowed with obvious planetary targets I must say the section membership has done remarkably well and I thank them for their efforts
Looking Forward.
 
So what can we look forward to over the next reporting period? Mercury moves into inferior conjunction between the Earth and the Sun on the 16th of October, becoming a morning object and putting on its best UK morning show of the year. It will reach its greatest elongation from the Sun (western elongation) on the 1st of November when it will be 19 degrees away from the Sun and around 11 degrees above the horizon at around 0615 ut on that date; exact time and elevation depends on latitude.
 
Venus appears very close to the Sun at the start of October and moves into Superior Conjunction behind it on the 25th. From then it moves into the November evening sky but is only visible very low in the south-western sky at sunset. Similarly Mars is visible in the evening sky in October, setting two and a half hours after the Sun, but is low, dim and distant. Daytime infra-red imaging may show larger surface features but cloud/atmospheric details will have to wait for the next night-time apparition.
 
Jupiter will improve rapidly during the period, starting as a morning object visible in the hours before sunrise, by the end of November it will rise before midnight, transit by 0500ut and reach more than 55 degrees of elevation. Cloud features will be revealed in great detail and we will find out if the equatorial band hinted at above has really formed or not.  Of interest for watchers of Jupiter’s moons, Io passes in front of Callisto on the morning of the 24th of October from between 0824 ut and 0831 ut. This will obviously be in daylight but should be eminently visible, weather permitting, and can be imaged as long as the daylight safety precautions already referred to are strictly adheared to. I would recommend a monochrome camera and an infra-red pass or deep red filter to make the best of this but Carl Bowron has proven that one-shot-colour cameras can also be very effective for daylight imaging of the major planets.
This occultation of one moon by another happens because we are entering a period where the orbital plane of these moons is tilted nearly edge-on to our line-of-sight from Earth.  There will therefore be a series of mutual events between the four Galilean moons, Io, Europa, Ganymede and Callisto; occultations where one moon passes in front of another, and eclipses where the shadow of one moon covers the visible face of another.
This lining-up of the orbital plane of the moons with Earth happens twice during Jupiter’s 12 year orbit and, on this occasion, will last into August next year. With a bit of work the freeware program Winjupos can be used to show the exact date and time for such events from your location.
Saturn is on the far side of the Sun and drawing closer to conjunction which occurs on the 18th of November. Daylight observation is possible up to perhaps a week either side of conjunction but no great detail will be discernible. Out of interest a close conjunction between Saturn and Mercury occurs on the 26th of November with Saturn passing just 1.7 degrees to the north; unfortunately this is only likely to be visible for a few minutes around 0740 to 0745ut very low on the south-eastern horizon 'though, again, daytime infra-red imagery is possible.
 
Uranus is still well placed throughout October and November. Reaching opposition on the 7th of October the planet will shine at magnitude 5.7, on the edge of naked eye visibility, around 38 to 44 degrees above the southern horizon depending on latitude. At 19 astronomical units distance, some 2845 million kilometers, it will show a visible disc just 3.7 seconds of arc across and the challenge is for well equipped amateurs to resolve near infra-red cloud features in its upper atmosphere.
 
Neptune leads Uranus across the sky, transiting at 2230ut on the 7th of October some 23 to 27 degrees above the southern horizon. At magnitude 7.8 it is a telescopic object but is well worth a visit before beginning serious observation of Uranus. Please let me know how you get on with all your observations and I will report your findings here in two months’ time.
Alan Clitherow.