The opposition of Mars, 2012: Part I

2019 October 2

Richard McKim

Introduction

In this report we adopt the convention of numbering Martian  Years (MY), beginning at the 1955–’56–’57 apparition at the dawn of the Space  Age. Each year begins at Northern Spring Equinox, at Ls (areocentric longitude)= 0°.  Table 1, from Meeus (1983),  lists the first 32 Martian  Years.

Third in the present series of aphelic encounters, Mars was undergoing  late  northern  spring  at  opposition  on  2012  Mar  3  at  Ls= 78°, when it was very close to aphelion (Ls= 70°).  The planet lay in Leo with a relatively favourable declination for European observers of +10° that did not unduly disadvantage our Australian contributors.  The latitude of the sub-Earth point (or disk centre), De,  varied  from  –20°  in  2011 mid-May,  falling  to  zero  in  late  July and  rising  to  nearly  +24°  in  December.  It  remained  high  at  +22°  at opposition,  rising  further  to  +26°  in  2012  June  and  decreasing  to zero in November.

Mars  was  closest  on  2012  Mar  5,  at  101  million  km,  with  a  disk diameter  (D) of  13.9″; almost the  least possible  at  opposition, and the smallest of the current cycle. D remained above 6″  from  2011 Nov 3 till 2012 Jul 20. Key seasonal dates are given in  Table 2. Observing  conditions  in  the  UK  were  typical,  but  the  weather deteriorated considerably after opposition. 110 contributors sent 5,226  images  and  724  drawings;  5,950  observations  covering  2011 May 12 (Ls= 291°, D= 4.1″  (Akutsu image)) to 2013 Feb 14 (Ls= 264°,  D=  4.0″  (Adamoli drawing)). Days per month logged (actual/possible)  were:  2011  May,  2/31;  June,  3/30;  July,  12/31;  August,  24/31;  September,  28/30;  October,  25/31;  November,  23/30; December,  27/31;  2012  January,  29/31;  February,  29/29;  March, 31/31;  April,  30/30;  May,  31/31;  June,  22/30;  July,  20/31;  August, 10/31;  September,  2/30;  2012  October,  0/31;  November,  0/30;  December,  0/31;  2013  January,  2/31  and  2013  February,  4/28. 

We covered  92%  of  the  span  of  a  martian  year  (albeit  fragmentary 2012 post-September), during MY  30–31. Akutsu,  Maxson,  Morales  Rivera,  Morita,  Peach  and  Willems each  took  more  than  150  images,  with  Maxson  securing  647  on 156  dates  (including  much  early  morning  work),  and  Willems  (a new contributor) sending 678. I. D. Sharp obtained images from Barbados  during  2011  December.  Abel,  Adachi,  Adamoli,  Bailey, Beish,  Konnai,  McKim,  Macsymowicz  and  Niechoy  each  made more than 30 drawings. The most successful colour imaging was done by compositing individual  red  (R),  green  (G)  and  blue  (B)  filter  images.  Some  observers display individual channels separated from a one-shot colour image, but ‘blue’  channel separations are misleading and useless as they encompass a much wider waveband than any ‘blue’ filter…. (continued)

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