This was a more interesting reporting period than the last one with contributions by amateurs, including one from the SPA, establishing the rotation period of atmospheric features on Neptune as well as the first observation of Mars in its coming apparition. Having said that, I am going to start with observations of the photogenic planetary conjunctions that took place during this period.
The first was between Venus and Mars in early October. These two planets rose within 10 degrees of each other for the first three weeks of October but on the 5th and 6th of the month they were really very close together; late in the afternoon of the 5th they were visually just less than 13 minutes apart, less than a quarter of a degree and the closest they have appeared since November 1995! The best time to see for UK observers was early on the mornings of the 5thand 6th with the separation still less than 25 minutes.
Mike Feist sent in a number of detailed visual observations of the conjunction covering the 3rd, 4th and 6th and I was able to take a wide-field image on the morning of the 5th which just managed to capture both planets; Venus was obvious but Mars was considerably fainter at magnitude +1.8 and even fainter still once atmospheric extinction was taken in to account. Mike reported that, using his low-powered spotting scope at 12-times magnification, the two planets filled just a third of the field of view on the 4th of October reducing to around one-sixth of the field on the morning of the 6th.
The next conjunction was around the 13th of November, this time between Venus and Jupiter. On that morning, between 8 and 9 am UT, the two planets were just less than 16 minutes of arc apart and both were bright and obvious with Venus showing a 97% illuminated disc some 10 seconds of arc across and shining at magnitude -3.9. Nearby Jupiter was three times larger in diameter but slightly dimmer at magnitude -1.7. Simon Kidd imaged the pair in full daylight, at 1024 UT using a small ED80 refracting telescope and an ASI224 one-shot-colour camera; he even managed to capture the equatorial belts on Jupiter. Stuart Atkinson also took photos of the event, on both the 12thand 13th, against the backdrop of the pre-dawn horizon and showing the rapid apparent motion between the two planets over just 24 hours.
Planetary conjunctions, while interesting and photogenic, do not possess much scientific value but the fact that the world continues to operate normally after each conjunction can, perhaps, be used to refute the predictions of some of the wilder elements of the astrological community!
And with that rather clumsy segue I will now discuss some scientifically useful observations made by amateur astronomers. In the second week of October observations of Neptune were made by three non-SPA amateurs which showed the movement of a newly-found storm cloud in the atmosphere of the planet; Marc del-Croix on the 10th and Milika & Nicholas on the 14th. Add to these images taken by our own Martin Lewis on the 12th of October, clearly showing this feature, and the drift-rate of the cloud could be estimated using multiple observations over an 87 hour period. This worked out at 46 degrees of drift in longitude per 24 hours and allowed the calculation and publication of ephemeris for the feature, as seen on the SPA website.
Martin Lewis again caught the feature in motion on the 15th of October and the 1st of November. These were also published as a news item on the website along with small animated gif movies demonstrating the drift of the storm over time. This outstanding work was taken using a large Dobsonian telescope on a tilting equatorial platform and a monochrome planetary video camera fitted with a Baader 610nm long-pass filter; a filter passing deep-red and near-infrared light to the camera sensor. Dave Finnigan used the same ASI camera and filter on his 12-inch Schmidt-Cassegrain telescope on the 5th of November and captured the tiny disc of Neptune very clearly. Unfortunately the ephemeris predicted that the cloud feature would not be visible at the time of Dave’s observation and this proved to be accurate.
As a note for observers who might like to try this kind of challenging work in the future; it is very helpful if you can, as well as capturing either Uranus or Neptune, also capture one of the brighter moons in the image as this helps to pin down the exact time of the observation and so help with estimates of drift of any cloud features seen. I should mention that Martin Lewis was easily able to resolve the moon Triton and, in fact, used this ability to observe the occultation and re-emergence of the star UCA 4 410 from behind Triton on the 15th of October.
Moving on to Uranus both Martin and Dave made excellent photographic observations of the nearer of the two ‘Ice-Giant’ planets; on the 1st of November for Martin and on the 16th for Dave. Identical cameras and filters were used here, as had been used on Neptune, as only subtle shading can be seen in visible light on either planet; bright cloud features only appear in the infrared. No discrete cloud systems are currently visible but distinct pale shading is seen from temperate northern latitudes up to the pole. With a good Uranus image under his belt, Martin was able to ‘complete the set’ for 2017 and sent me an amazing collected-image running through all the major planets from Mercury to Neptune as captured by him this year; very inspiring stuff. (please see below).
Having talked about those distant planets I will now briefly mention the two closet planets to Earth. Venus was observed on the 25th of October by Dave Finnigan, by me on the 26th and by Carl Bowron on the 27th. Venus at that time was drawing very close to the Sun in the morning sky with just 19 degrees of separation at that time. Dave used a monochrome camera and a filter passing light in the near ultra-violet and managed to capture a dark central band around the planet while observing in full daylight at 0906 UT.
This is a difficult thing to do as UV wavelengths are badly dispersed when the planet is viewed in darkness at low altitude but thermal turbulence equally destroys image quality later in the day as solar heat builds in our atmosphere. Viewing early to mid-morning can provide a useful compromise with the planet at a sensible altitude but with little heat in the air. My own attempts were made at three frequency bands, one in the near UV and two parts of the near IR, but none showed any clearly identifiable cloud features. Carl’s image was taken with a colour camera and shows the nearly full face of Venus (95%) illuminated, in a deep sulphurous yellow.
Finally I come to Mars. Late in the period, on the 17th of November Simon Kidd targeted the red planet in the morning sky and managed to capture detail. At just 4.1 seconds of arc across Mars was little bigger than Uranus and at 24 degrees of elevation above the south-eastern horizon there was a problem of atmospheric dispersion to contend with. Simon used an Atmospheric Dispersion Corrector (ADC) made by the ZWO Company; that is the manufacturer of many of the planetary capture cameras used by contributors to the section and is ideally matched to them. The ADC recombines the light dispersed as a refraction effect within our atmosphere and allows sharper images of low altitude targets. His North-up image shows a faint light ‘pin-prick’ at the position of the northern polar ice-cap, currently much reduced by summer in that hemisphere, along with the dark patches of Acidalia and Chryse Planitia in the North and Terra Meridiani in the South.
Most observers don’t start looking at Mars until it is over 10 arcseconds in size but modern photographic techniques can tease out detail much earlier in the season. This year and next, for UK observers, Mars will be seen at very low altitudes, especially approaching opposition in 2018. Observation early in the season has advantages in that Mars currently sits slightly higher towards the ecliptic, an advantage that will be lost as the season progresses!
Added by Alan Clitherow