Fellow gnomonicists:
For the past six months a team has been working on the sundial
design for the NASA Mars mission that will launch in 2001 and land on Mars
in 2002. The sundial's presence on the spacecraft (all 60 grams of it!) is
justified because we've been able to adapt, for gnomonic purposes, a
calibration device for the primary camera. I don't have time to go into
details now (fabrication of this dial will commence very soon), but it's
basically a post/gnomon (6 cm high) with 2 nodi on it for indicating both
the Martian time and the date on a 8-cm-square plate. The main difficulty
in the design is that a priori the orientation of the post is not known,
nor is it movable once the spacecraft has landed! All we know now is that
the gnomon will be approximately vertical at a latitude in the equatorial
region (site to be chosen next year)......Therefore, unfortunately, one
cannot calculate the hour lines and date lines beforehand. Instead, once
the spacecraft has landed, we will use the sun's shadow itself to determine
the gnomon's orientation, and then calculate the correct lines and
superimpose them on the Web images, which is how the world will be seeing
the sundial in action. (Don't worry - we'll tell everyone that the lines
are superimposed!) But this Web superimposition technique does mean that
one can have *dozens* of superimposed sets of lines to choose from - think
of all the dial furniture one can now have: time until Martian sunset,
aerocentric declination of the sun, Martian zodiac sign, length of
daylight, altitude angle of the sun, etc., etc.
By the way, the image at
http://astrosun.tn.cornell.edu/athena/xeducation.html is only a rough
approximation to the final design. More details later on the first (known)
extraterrestrial sundial.
Cheers, Woody Sullivan & the Athena Pancam
instrument team
******************************************************************
Prof. Woodruff T. Sullivan, III [EMAIL PROTECTED]
Dept. of Astronomy, Box 351580 tel. 206-543-7773
Univ. of Washington fax 206-685-0403
Seattle, WA 98195 USA
