DISC PARAMETERS FOR MARS 
 ----------------------
 2003 June 11
 John Pazmino
 john.pazmino@moondog.com
    This table is a general one for Mars at any time, not only for 
opposition. It starts with about the smallest disc that can reveal 
surface texture in homesize telescopes, 8 arcseconds. Discs step to 
the near maximum possible, 25 arcseconds, by 1/2 arcsecond. 
    Mars when around 10 arcsecond is at or near quadrature, 90 degrees 
west or east of the Sun. The timespan from west quadrature thru 
opposition to east quadrature is conventionally the viewing season for 
Mars. Or it is the period of apparition. 
    After east quadrature, Mars is usually still observable in the 
evening sky, even tho the disc is then getting much smaller. The table 
accommodates this extended viewing season by starting at disc diameter 
8 arcseconds.
    The power, magnification, is that needed to bring the disc in the 
telescope the same angular size as the Moon in the naked eye. Bear in 
mind that by eye the Moon presents vastly more structure and texture 
than Mars will ever show in a homesize telescope. The actual power 
employed on a given occasion depends on the stability of the sir, the 
optical quality and collimation of the scope, solidity and tracking of 
the mount, observer skill, among others. 
    The Earth-Mars distance is in both astronomical units (mean Sun-
Earth distance being unity) and in millions of kilometers. This 
distance is center-to-center, not face-to-face. 
    The lighttime from Earth to Mars (or, maybe, vice versa!) is in 
minutes and seconds. 'Light' means all electromagnetic signals, like 
radio, telemetry, video, and commands. A roundtrip is merely double 
this amount, neglecting delay or dwell at Mars. 
    The linear length on Mars for one arcsecond angular resolution is 
in kilometers. This is about the smallest feature discernible by 
homesize telescopes. Only the grossest markings are seen on a small 
disc, and then only if they are contrasty and well edged. The polar 
cap, when large and tilted to Earth, can usually be seen on all discs 
in this table from its white color against the orange body of Mars. 
 +----------------------------------------+ 
 | diam  pwr  distAU  distMKm  light  sec | 
 | ----  ---  ------  -------  -----  --- | 
 |  8.0  234  1.1694  174.940  9m44s  849 |
 |  8.5  219  1.1006  164.650  9m09s  799 |
 |  9.0  207  1.0395  155.503  8m39s  755 |
 |  9.5  196  0.9848  147.319  8m11s  715 | 
 | 10.0  186  0.9355  139.953  7m46s  679 | 
 | 10.5  177  0.8910  133.288  7m23s  647 |    
 | 11.0  170  0.8505  127.230  7m04s  618 |    
 | 11.5  162  0.8135  121.698  6m46s  591 |    | 
 | 12.0  155  0.7796  116.627  6m29s  566 |   | 
 | 12.5  149  0.7484  111.962  6m13s  544 | 
 | 13.0  143  0.7196  107.655  5m59s  523 | 
 | 13.5  138  0.6930  103.669  5m45s  503 | 
 | 14.0  133  0.6682   99.966  5m33s  485 | 
 | 14.5  128  0.6452   96.519  5m22s  469 | 
 | 15.0  124  0.6237   93.302  5m11s  453 | 
 | 15.5  120  0.6036   90.292  5m01s  439 | 
 | 16.0  116  0.5847   87.470  4m51s  425 | 
 | 16.5  113  0.5670   84.820  4m43s  412 | 
 | 17.0  109  0.5503   82.325  4m34s  400 | 
 | 17.5  106  0.5346   79.973  4m26s  388 | 
 | 18.0  103  0.5197   77.751  4m19s  377 | 
 | 18.5  101  0.5057   75.650  4m12s  357 | 
 | 19.0   98  0.4924   73.659  4m05s  358 | 
 | 19.5   95  0.4798   71.771  3m59s  348 | 
 | 20.0   93  0.4678   69.976  3m53s  340 | 
 | 20.5   91  0.4564   68.270  3m47s  331 | 
 | 21.0   89  0.4454   66.644  3m42s  324 | 
 | 21.5   87  0.4351   65.094  3m37s  316 | 
 | 22.0   85  0.4252   63.615  3m32s  309 | 
 | 22.5   83  0.4158   62.201  3m27s  302 | 
 | 23.0   81  0.4068   60.849  3m32s  295 | 
 | 23.5   79  0.3981   59.554  3m18s  285 | 
 | 24.0   78  0.3898   58.314  3m14s  283 | 
 | 24.5   76  0.3818   57.124  3m10s  277 | 
 | 25.0   74  0.3742   55.981  3m06s  272 | 
 +----------------------------------------+