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 |
+----------------------------------------+