Popular Astronomy

Share to Facebook Share to Twitter Stumble It More...

Section Report for February and March 2017

 Most of the section’s efforts were directed to Jupiter and Venus in this period but some monitoring of the weather on Mars was carried out and even little Mercury received some attention at the end of the period.

.

As reported and imaged by the section during the previous reporting period Jupiter’s cloud features have undergone some dramatic changes, particularly within its South Equatorial Belt (SEB). The two large tadpole-shaped bright storms previously seen within this ochre belt, near CMII 208 degrees, have developed into a chain of three and possibly four or more such storm-spots and may further develop as the planet moves towards and past opposition in early April. Observation started with Dave Finnigan, submitting images from the 3rd and 16th of February taken at both infrared (IR) and methane absorption-band frequencies. The later of these shows three bright spots in the methane band, being the Great Red Spot (GRS), Oval BA and the moon Io in transit across the disc; the disturbed area within the SEB does not currently show in methane images but was seen later in visible-light observations.
The area of interest is not always readily visible so Dave’s images from the 6th of March don’t cover it and nor does Simon Kidd’s excellent image from the 15th of March ‘though that does show tremendous detail in the turbulence area that follows the GRS as it ploughs along the southern edge of the SEB, as well as filaments within the Equatorial Zone and white oval storm activity within the North Equatorial Belt and into the northern temperate regions. Dave Tyler took the same scene a few minutes earlier than Simon and the two images are directly comparable in detail. Dave’s image is a composite of red, green and blue frames taken with a monochrome camera and the seeing was so good he took the unusual step of using the green frame to provide the detailed ‘luminance’ part of the image instead of the more commonly used red frame. Simon’s image was taken with a modern one-shot-colour (OSC) camera.
.
Of interest Robin Scagell used another OSC camera and an 80mm refracting telescope, an’ED-80’, to image Jupiter on the 17th of March and I attempted the same with a 100mm refractor on the 21st. This was done to show that modest apertures will still show the major features on view and, if you don’t happen to own a large ‘light-bucket’ of a telescope, I would still encourage you to try observing large and bright targets like Jupiter as the results can be surprisingly good, as well as scientifically interesting.
.
While Robin’s image is clearer than mine the SEB disturbances were not on show when he took it; mine does hint at the disturbances within the SEB and they are seen more clearly in an image from slightly later on the 21st taken with a 250 mm aperture Newtonian telescope. There are now three, possibly four or more storms disrupting the belt. Dave Finnigan’s images from the 22nd and 23rd of March also support this conclusion and show that the GRS is now noticeably more red than in previous months and very bright in methane images. I must also mention an excellent hand-drawn map of the features visible on Jupiter during the last apparition, submitted by Mike Hezzlewood and a Jupiter image taken by Steve Norrie on the 21st of March. Steve said he knew the image lacked detail but the seeing was very poor and he was happy to get any kind of result under the circumstances.
.
Venus was a splendid object in the late afternoon and early evening skies in this period and a number of observers made efforts to follow it in visible light, IR and ultra-violet (UV) bands. Dave Finnigan’s UV image from the 3rd of February show bright patches away from a darker equator while Mike Lewis caught very subtle detail on the 4th within the narrow, 37% illuminated, phase. He has been trying new processing techniques to enhance detail, in this case using deconvolution filters within the software ‘Astra Image’ to sharpen faint detail; one has to say this has been very successful.  His IR image of the same date shows, as is usual, only a uniform cloud top with no discernible detail.
At around that time I received via the SPA website contact form a number of phase estimations for Venus from a new contributor, RM Steele, however the return email address was incomplete so I was unable to reply. If you do read this, please try and contact me again and I will acknowledge your work more fully in these reports.
.
Alan Heath submitted his usual excellent and detailed observations of Venus, following it until the 20th of March when the planet inconveniently decided to disappear behind buildings and became unobservable from his site. Visually he has reported in the past that the equatorial area often appears perceptibly brighter than the cusps as the phase shrinks, however during these observations the visible limb seen uniformly bright from cusp to cusp right up until the 15th of March, after which the cusps assumed there more normal ‘dull’ appearance. Alan also reported that winter storm ‘Doris’ was strong enough to physically move his observatory, but without damage to anything but some guttering!
.
Mike Hezzlewood submitted a number of sketched observations of Venus including one from the 17th of February. This is beautifully executed and shows subtle shading and bright patches around a darker equator. Alan’s observation from that date reports no clear detail but reports possible darkish markings while Dave Finnegan’s UV image shows uniform shading from limb to terminator with no obvious detail. Martin Lewis’s UV image from the next evening is very similar with, perhaps, a hint of subtle mottling but no more. Moving into March and Mike’s drawing from the first again shows subtle detail only with “…a very narrow shadow extended from the southern cusp. Several other extensions protruded from the terminator following the pattern of atmospheric rotation”.
.
By the next observation on the 15th of March the visible phase had fallen to a narrow sliver of light with both Carl Bowron and Simon Kidd taking the opportunity to record this beautiful and somewhat ethereal view of our sister planet; Mike submitted a final drawing from the 20th when he reported the visible phase as just 1.9%.
.
Mars has sat close by Venus in the period and Martin Lewis took the opportunity to observe and image it with considerable success. At the time of his first report, on the 4th of February, Mars was showing a disc just 5 arc-seconds across and by the time of his last report on the 24th of March this had fallen to just 4.3 arc-seconds. As you would expect captured detail is large-scale rather than sharply defined but this goes to show that Mars can now be followed for an extended period; just a few years back most observers stopped reporting when it fell below 10 arc-seconds in apparent size. His image from the 4th of February has the Tharsis region near the centre of the disc with hints of Arisia Mons, Pavonis and Ascraeus mons; the image is shown south-up and the tiny south polar ice cap is visible at the top.
On the 18th of February Syrtis Major and the Hellas basin are visible near the limb with Sinus Sabaeus clear on the central meridian. Detail is less distinct in an image from the 15th of March but Solis Lacus, sometimes called the “eye of Mars” can be seen with Tharsis again on the central meridian. Reported elsewhere, minor dust storms have been seen near Aurora Sinus, close by Solis Lacus, but these are not obvious from Martin’s images. Finally his image from the 24th of March has Hellas on the limb with Sinus Sabaeus again visible, part of Mare Acidalium also visible, the rest disappearing behind atmospheric cloud features at the extreme north. The south polar cap is no longer shown despite being tilted towards us.
.
I learned recently that some planetary imagers have been using the kind of UV filter, commonly used to image Venus, on Mars to enhance atmospheric cloud detail. I will try this myself some time but not until Mars is much better placed for observation from the UK. Mike Hezzlewood also submitted a small sketch of Mars from the 1st of March in which both Hellas and the Mare Cimmerium may be discerned.
.
 Finally Dave Finnigan took the trouble to image Mercury on the 24th of March. He used an IR-pass filter to cut through the poor low-altitude seeing conditions and caught a hint of surface albedo features with his ASI120 monochrome camera; excellent work on a very challenging target.
Submitted by Alan Clitherow.
 
 
 

Added by: