Mars Section Circular No. 7

1999 June 1–July 15

General

This Circular summarises the period 1999 June 1 (Ls 147 deg, D 14.2 arcsec, decl. –10 deg.) to July 15 (Ls 171 deg, D 10.3 arcsec, decl. –14 deg.). Mars has been an evening object, and to see him at reasonable altitude from the UK, near the meridian, has meant picking him up against a light blue sky. Some of the early June observations have already been reported in the last Circular. Further contributions have come from B. Adcock, T.W. Leong and M. Valimberti (CCD images), M. Adachi, D.L. Graham, D.P. Joyce, P. Lyon (photographs with 20-cm SCT), P.W. Parish, J.D. Shanklin, D.M. Troiani, and A. Van der Jeugt. Peter Lyon managed some excellent photographs from his site in Birmingham, and I quote in extenso from his letter of June 21 (below), to pass on details of his experiments concerning film and technique. His are the only photographs received in 1999; last apparition I received photographs from just two observers. There is no denying the great aesthetic value of a nice planetary photograph, and I hope observers will still make them, if only for the sake of historical continuity and as a true test of skill. He prefaces his discussion with the comment that given the pace of digital camera progress, the details may be less useful in 2001!

Photographing Mars in 1999 : Peter Lyon

Exposure lengths

The criteria will differ with every telescope/camera set-up, but on my portable C8 SCT I have found that with an exposure of 2 seconds or more the initial vibration (about 0.3 seconds) due to the camera shutter does not show up. For Mars at image scales above f/100 this is, in any case, the most useful exposure required on colour slide films which are sufficiently fine grained to record fine detail. I favour 2-second exposures to avoid excessively precise polar alignment, which for the Moon are short enough to test for vibration even without a special lunar drive rate.

Films

Initial tests on Agfachrome RSX 50 Professional colour slide film simply served to confirm an exposure for Mars (from the UK) of 2 seconds at f/110, but the film, producing good colours, seemed to lack contrast, and was far too coarse-grained for martian detail. Kodachrome 25 at f/110 with 4-second exposure produced good contrast, fine grain and a vivid green colour (for Mars!), so was definitely not suitable. Kodachrome 64 at f/120 and 2-second exposure perhaps suffers somewhat from reciprocity failure. The grain, while coarser than the Kodachrome 25, was reasonably acceptable, but the colours are (not surprisingly) those of ‘old’ Mars photographs – a pinkish hue for the desert areas and a mauve tint to the dark markings (which have reasonable contrast). Fujichrome Velvia (50 ISO) at f/110 and 2-second exposure must, for this selection of films, be regarded as the definitive film for Mars. The colours are recorded, with no hint of any shift in colour balance, precisely as a pleasant orange hue for the deserts, with quite neutral dark markings, and the smoothness of very fine grain completely surpasses both of the Kodachrome films. I have no doubt that this film, at this image scale, could record all detail that the telescope can resolve, without resort to high contrast black-and-white films. The contrast of the Fuji Velvia, although not dramatic, is well up to the task, and is quite amenable to enhancement by slide duplication techniques.

BAA and other observations (mostly concerning the polar regions), 1999 June 1 to July 15

I have carried the observations up to July 15 in order to document the most interesting phenomenon of the moment: the appearance of the N. polar hood. Signs of a permanent polar hood mark the late June observations, and occasionally before that time. In Circular No.6 the ‘polar cyclone’ of HST was described: such large white clouds are often seen as a precursor to the formation of the hood. Two further events were witnessed by members of the OAA in May and June.

Several observers in late June portrayed the cap as being diffuse at the edges, and sometimes less bright than earlier on. The latest CMO (OAA) No. 220 to reach the Director describes the period June 1–15 as observed from Japan. As late as June 14th Olympia and Rima Borealis were still visible. During all that period the NPC was observed. On June 18 (Ls 157 deg.) under CML 322–338 deg. the Director found the S. edge of the NPC less sharp and the cap slightly less bright. The NPC seemed sharper on the 20th under CML 295–298 deg., but seeing was mediocre only. And on the 24th, CML 259–267 deg., there was a cap with brighter haze to its south. Bad weather then intervened. Using Michael Hendrie’s 15-cm OG on July 9 (Ls 167 deg., CML 96 deg.) the Director had an excellent view, when a definite change in the aspect of the area was evident; the slightly less bright hood was larger and somewhat diffuse over the N. limb. He found the hood brighter and a little larger still on July 11 under CML 86 deg. My later observations constantly show a hood.

Meredith’s sketches suggest an increase in the size of the NPR in late June: an overlying hood forming? Elisabeth Siegel, June 19, CML 302 deg: ‘It seems to me that the NPC has grown a little bit since the beginning of June’ And Teichert on June 17–28 found the NPC faded, and blurred at the edges. The combined work of Cidadao and Parker seems to show a polar hood present during June 25 to July 7. In 1999 the hood has therefore appeared to cover the cap entirely by early July. (Ls 163 deg. on July 1.) The receipt of further data will enable these limits to be refined later. In any case, this is typical seasonal behaviour. In 1984 the hood appeared at Ls approx. 161 deg., for instance, though it was not constant at all longitudes to begin with.

At the same time, throughout June and July we have had a very bright S. limb, which exhibits still brighter patches from time to time. Especially bright parts are those corresponding to northward incursions over Hellas, SW Thaumasia (or Claritas) and Argyre. This entire area is foreshortened and hard to observe well except in very good seeing. My impression is that it is (at least from July onward) now the ground cap, showing as it does a fairly sharp N. boundary: I have not yet tried to analyse the precise transition from one to the other. (In the past, I have looked for the visibility of the cap in red light, while the brighter patches within the hood have been taken as signs of the ground cap showing through. More data please!) In 1984 the SPC was present from about Ls 161 deg., at the same time as the NPH covered the NPC, in fact.

No certain reports of dust activity have come to hand. No changes in the surface features have been detectable upon the rapidly shrinking disk. Reports of white clouds continue to be received, but I do not intend to describe them further here, suffice to record that the ECB appear to have finished, and cloud activity generally, except in the polar regions, seems less prominent.

The BAA martian dust storm Memoir This Memoir is now in press, the corrected proofs having been returned to the printers. (For details, see Memoir.) Other recent publications Don Parker et al. describe the ALPO 1997 observations in Icarus, 138, 3–19 (1999); Ted Stryk published his observations of 1996 January, when significant dust activity was inferred from the CO microwave data of R.T. Clancy, in J. Assoc. Lunar Planet. Obs., 41 (2), 76–77 (1999); Paolo Tanga has written up the UAI’s 1995 Mars work in l’Astronomia, 1999, No. 1, pp.2–11. The future reports of the Mars Section Although preliminary accounts of the 1995, 1997 and present apparitions have been published, final reports have yet to be completed for all these years. If anyone reading this has good data for any of these years, but has not yet submitted it, please

do so now. With the completion of the Memoir, I shall be working on final reports on 1995, 1997 and 1999 during the autumn.

The next Circular

The apparition is all but over for UK observers, given the low altitude and small disk size combined. I will therefore issue just one more Circular this apparition. So let me have your July and August observations by September 15, so that the final Circular can be issued later that month. Of course, do keep trying to observe even longer if you can, and send in your results whenever possible. Good observing!

Richard McKim, Director

1999 July 18