September 11th Remembrance

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Published: 05 September 2011

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September 11^th is a time of remembrance. At Freedom High School in Woodbridge, Virginia stands a large sundial dedicated in 2004 with four inlaid plaques. The plaques are arranged on the ground such that the gnomon shadow tip falls on them at  8:45, 9:03, 9:37 and 10:07 AM, the times of the four air crashes.  Near the sundial is a low, black granite panel commemorating the citizens of Prince William County that lost their lives on September 11^th, and the names of those citizen are on bricks surrounding the sundial.

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Two Worlds - One Beginning

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Published: 26 February 2021

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Everyone is excited about the landing of Perseverance, the Mars rover.  If you look closely at the first panorama of the Martian landscape you will see on the equipment bay of Perseverance the Mastcam color calibration target.  It sort of looks like it could be a sundial.  In 2004 a similar calibration target was used as the first Martian sundial, designed by Dr. Woody Sullivan and Jim Bell with the support of The Planetary Society and Bill Nye, "The Science Guy" [See PDF at bottom].  Is the Mastcam color calibration target a sundial as well?  Here is Dr. Sullivan's answer to a group of sundial enthusiasts (2/25/2021):

"The short answer is “No”. The longer answer follows. The new object on Perseverance (officially the "photometry calibration target") has obvious similarities to the Mars dials on Spirit and Opportunity that landed in 2004, and in fact it  is a technological and aesthetic “grand-daughter” 17 years later. (The intervening generation is the Curiosity rover, which landed in 2013 and is still alive). The Mars dials that a small group of us designed and fabricated and then occasionally “used” to read Martian time were a great experience for me.

"But after over a decade of Spirit and Opportunity, I decided not to get involved in any future NASA missions — they gobble up a lot of time! The science and fabrication of the new calibration target (as for Curiosity) is led by a group at U. of Copenhagen. 

"Nobody has ever done anything with the orientation of the shadows cast by the “gnomon” on Curiosity  and I’m sure nobody will for Perseverance either. By the way, independent of gnomonics, the vertical tube has a vital scientific purpose: its shadow on the gray and colored patches allows one to calibrate camera images properly in shadow  as well as sunlight.

"The various symbolism and messages on Perseverance also stem directly as heritage from Spirit and Opportunity . You can find a tremendous amount of detail about all aspects of the Perseverance cal target (including construction) at https://mastcamz.asu.edu/mars-in-full-color/ [See PDF at bottom]. The feature I like best is the motto  “Two Worlds, One Beginning”, which nicely refers to Spirit and Opportunity ’s  “Two Worlds, One Sun” as well as early solar system history and the possibility of early life on Mars. (Curiosity has the terrible motto “To Mars to Explore”.) 

"Nevertheless, I watch the procession of missions with great astrobiology interest. And someday I will write up the whole Mars dial experience, including many Martian landscape images in which it appears, and how a student and I were actually  able, using its shadow, to measure the Martian analemma at local mean (“clock”) noon over a Martian year ( =  1.9 Earth years).

— Woody Sullivan

Prof. (Emeritus) Woodruff T. Sullivan, III   
Dept. of Astronomy & Astrobiology Program  Box 351580
University of Washington
Seattle, WA 98195  USA

Attachments:

Mastcam-Z_Cal_Targets.pdf	[ ]	6721 kB
The Planetary Report-2004-v24n1.pdf	[ ]	1426 kB