Mars Section Report No. 4

1997 January 1–31

General

The disk diameter increased from 8.0 to 10.6 arcsec. I refer to published OAA data (CMO No. 183) for comparison. New contributors this month were P.Devadas (India), Prof. C.M.Gaskell (USA) and C.Meredith (UK). Others are known to have unreported observations! The NASA probes are en route, but Mars 96, the Russian one, failed; the latest details have been given in Sky and Telescope (1997 March, p.20) and elsewhere. William Sheehan’s excellent new Mars book is also reviewed in the latter magazine.

North Polar Region

The North Cap remained large and bright to all observers, with a dark collar. No colour other than white has been directly reported to the Director in the period reviewed, but in CMO No.183 H.Ishadoh (31-cm refl.) is reported to have noticed a slight dullness coupled with a brownish tint ‘from November or before’, until Dec 16. The Japanese account fails to mention any particular CM longitude (or CML range), which may be important. From Dec 24 the cap seemed normally bright again to Ishadoh; the brownish tint partly confirms Schmude’s December 20 observation (see BAA Report No. 3). Few UK observations for December are to hand; they reveal nothing unusual (nor do the other Japanese data). Devadas commented that by Jan 14 the NPC seemed perceptibly smaller than earlier, which is to be expected from the seasonal date. The Director has not yet measured any of the images submitted for latitude.

Surface features

In the second half of December and the first half of January, OAA observers remarked upon the colour contrast between the bluish maria to the south and the brownish Utopia to the north. Doubtless these apparent tints will differ from their true colours, but the difference in hue is undoubtedly real. This difference has been remarked upon very many times by past observers at aphelic apparitions: for example, the BAA Mars Section in 1935, G.de Mottoni in his beautiful coloured charts for 1952, Capen in the 1960s, Antoniadi and Slipher in their observational notes, and in the seasonably comparable epoch of the early 1980s by the BAA and other organisations. Devadas (36-cm refl.) on Jan 20 saw Solis Lacus well: it was quite large and dark, as in 1995. (Is it finally fading again on the southern following side, as noticed in the 1995 CCD images?) Tithonius L. and Phoenicus L. were also well-marked. Devadas and Meredith found the foreshortened Mare Sirenum somewhat poorly defined. Some of the martian volcanoes have shown up on mid-disk as dusky spots this month.

Dust storms (yellow clouds)

The deserts appeared their characteristic light orange, dust-free colour.

White clouds

Examples only, given that many observations still remain unreported: Devadas, Jan 4, CML 253 deg., Elysium lightish preceeding the CM; morning cloud over N. Aeria–Arabia. Devadas, Jan 14, CML 157 deg., Elysium lightish on the morning limb. [OAA observers found Elysium quite dull or only slightly light on the evening side (late December to early January), but light to the west of Propontis I, when immersed in the a.m. limb haze (mid-January). They found Alba apparently variable; in mid-January it was sometimes lightish from midday to evening]. Devadas, Jan 20, CML 96 deg., Chryse–Xanthe bright on evening terminator, and Arcadia–Tempe lightish on mid-disk. Warell e-mailed the Director that the Tharsis orographic clouds were ‘very evident’ on January 24.

Richard McKim, Director