Observing Mars in 2005

Mars will be in perihelic opposition again on November 7 when its disk diameter (just exceeding 20 arcseconds at closest approach) will be nearly as large as it was in 2003. It will however be much higher in the UK skies this year, and I hope that as many members as possible will support the Section with their visual and CCD observations.

Mid-spring in the southern hemisphere of the planet, Ls = 225º, is reached in the first week of June. With a disk diameter of 8 arcsec by then, it is time to start observing. The period from martian southern spring until midsummer is that in which large dust storms have often developed in the past. The 2001 opposition witnessed a seasonally very early planet-encircling event comparable only with the great storm of 1971. The seasonally latest such storm to begin was that of 1924 at Ls = 311º.

We shall be well-placed to record the recession of the South Polar Cap during 2005, although only a few early observers will have caught it at the start of spring. In terms of seasonal date at opposition we shall be later in the martian year than in 2003. The most similar past oppositions from each 15- or 17-year ‘cycle’ during the history of our Mars Section are 1894, 1911, 1926 (the closest in seasonal date), 1941, 1943, 1958, 1973 and 1990. (For the last three of these, Ls at opposition was 329º, 307º and 340º, respectively.) The various reports upon the great 2003 opposition and the previous ones mentioned (all of which are described in the Director’s BAA Memoir Telescopic Martian Dust Storms) give a very good idea of what observers should look for in 2005.

Observations should be sent to the Director at frequent intervals. The report form can be copied from this web site, and BAA members in the UK can obtain a printed copy from the Director. The Section programme and maps of the planet appear on this web site, and are also included in the BAA Observing Guide (obtainable from the Association’s office at Burlington House).

The rapid decrease in the apparent disk diameter after opposition is well illustrated by the accompanying CCD images acquired by Damian Peach in 2003 – the first of them with a 25-cm (f/55) Schmidt–Cassegrain on La Palma, and the others with a 28-cm (f/31) Schmidt–Cassegrain from the UK. Make the most of the period from 2005 July to 2006 January, during which the disk diameter will exceed 10 arcsec. Good observing!

Richard McKim, Director