Planetary Section Report; February and March 2018

As with the last reporting period, this period was not rich with easily accessible planetary targets however the section managed some excellent observations demonstrating, in particular, the very dynamic nature of the Jovian atmosphere. Having said that, I will start with something of a disappointment which was that no-one reported observing Mercury during what was its best evening apparition of the year for the UK.

Greatest eastern (evening) elongation of Mercury from the Sun was on the 15th of March and a few evenings either side of that date would have seen the innermost planet well placed for observation in the western sky from the UK, shortly after sunset. Sadly the weather did not play ball over this period so I received a number of rather frustrated negative reports from the section as its members tried to find a conveniently placed hole in the clouds. This is a shame as in recent years imagers have managed to capture albedo features on Mercury, particularly by using monochrome cameras and infra-red filters. I’m sure as technology develops more features will start to become visible on this small but fascinating world.

The visibility of Venus improved markedly late in the reporting period as it began to stretch away from the Sun in the evening sky and moves towards its own greatest eastern (evening) elongation later in the year. I am grateful to Steve Norrie for inviting me to his home in eastern Scotland for an evening of Venus observation on the 29th of March. There I was able to admire his excellent observatory set-up and to use his 127mm Makzutov Cassegrain telescope to view Venus while he grabbed some video images with his Celestron C9.25. Venus was playing hide-and-seek with us through extensive bands of cloud but Steve was able to grab just enough data to produce an interesting image.

By using a monochrome camera and IR-pass filter (as suggested above for Mercury) Steve caught some subtle mottling in the atmosphere of Venus along with bright spots near the sun-facing limb of the planet. With so little data available to make this image, and with Venus at such a low altitude when it did appear from behind the clouds, it is not clear if this detailing is real or if it arises from atmospheric distortions exaggerated by the image stacking process; however the 82% illuminated disc is suitably sharp and the atmospheric details are interesting so I am very grateful to Steve for supplying the image, as well as for the coffee and biscuits! Both infrared and ultra-violet filters can capture cloud detailing on Venus and these can be followed to show atmospheric rotation; I hope to see more such images in the next reporting period.




Mars was not well placed being both distant and very low in the sky as seen from the UK; however it grew above 5 arc-seconds in apparent size at the beginning of February and reached over 8 by the end of March so some detail was on view to careful and patient observers. Michael Hezzlewood sent me an excellent observational drawing made on the morning of the 20th of February when he was able to get decent seeing conditions despite the low altitude; he has kindly picked out the surface details that he was able to recognize. His drawings are miniature works of art so I am very happy to display them here to a wider audience. Mars has reached the season where cyclonic storms may become visible on the morning side of the northern polar regions, particularly near Baltia and Mare Boreum and, perhaps somewhat later on, near Utopia; I hope more observers will turn to this fascinating planet in the next reporting period.

As I have mentioned before, the major planetary targets are all going to be seen at rather low elevations from the UK over the next few years so observers should consider investing in an atmospheric dispersion corrector (ADC); these devices have fallen considerably in cost recently and greatly improve the detail that can be seen on low altitude targets.

Just like Mars, Jupiter had to be sort-out in the early morning sky during this period; however it’s much larger apparent size and greater elevation meant that considerable fine detail is on show. Larry Todd sent images from the 12th and 18th of February as well as the 3rd of March, the latter catching a very-clearly defined shadow transit of Io. Alexei Pace sent images from the 10th of March with the Great Red Spot (GRS) just rotating into darkness on the western limb and Steve Norrie caught Jupiter on the 29th of March in almost exactly the same aspect as Alexei’s image. I have compiled three of these images with one taken in May 2017 to show the obvious changes that have occurred in the Jovian atmosphere: All these images are presented north-up.

If we look at the 2017 image first we can see that in the southern hemisphere that Oval BA sits on the southern edge of a broad, empty pale zone with only faint ghosts of a dark belt trailing away from it; the South Equatorial Belt (SEB) is considerably disturbed by a long trail of white turbulence and that the North Equatorial Belt (NEB) is generally calm and of only slightly less width than the SEB. Above the NEB sits an obvious pale-orange band being the southern element of the North Temperate Belt; that is the NTB(S). Above this sits three thin pale zones and two darker belts before we reach the dark cap of the north polar regions.

In contrast the 2018 images show considerable change. A dark South Temperate Belt (STB) has appeared, distinct around most of the planet’s circumference, while the SEB appears much more settled but with a distinct dark southern border. In contrast the NEB is thinner and considerably disturbed, showing huge wave action and obvious white-oval storms cutting into the dark band; one of which is the long-lived storm White Spot Zulu (WSZ) which has rarely been more obvious. Very large dark features sit on the southern edge of the NEB and extend huge festoons into the equatorial Zone which is, itself disturbed and shows a narrow Equatorial Band (EB) over at least half the planets circumference. Above the NEB the NTB(S) is still distinct and orange in colour but north of that the multiple banding has merged into an expanded polar cap. Foreshortening effects often means that both polar regions appear rather bland as seen from Earth but it is interesting to note that images taken from the Juno probe currently looping around Jupiter from pole to pole show these regions to be as highly active as the rest of the planet.

Reports elsewhere suggest that a large south-tropical disturbance is interacting with the GRS so I am particularly looking forward to seeing images from that area in the next reporting period. As Jupiter steadily improves in visibility I would also like to confirm reports that White-Spots Alpha and Delta are now as big and as obvious as White-Spot Zulu. I would like to thank the section for its continuing support and contributions and wish you all clear skies for the next reporting period.

Alan Clitherow