A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Paul Hirose
Date: 2018 Jun 8, 22:18 -0700
I have a photographic tripod with a metal ball bull's eye level. The thing is almost useless. It lacks the sensitivity and smoothness of a bubble. The Apollo 11 passive seismic experiment had a similar device, and Buzz Aldrin had trouble centering the ball. "I'm having a little difficulty getting the BB to go in the center. It wants to move around and around on the outside." Neil Armstrong came over to help and wasn't any more successful: "That little cup is convex instead of concave." "I think you're right... Houston, I don't think there's any hope of using this leveling device to come up with an accurate level." They told Aldrin to level the seismic experiment by eye and press on. A few minutes later Houston requested a picture of the ball. Armstrong volunteered to return to the experiment and take the shot. "Would you believe the ball is right in the middle now." The laser reflector assembly also had a level. Armstrong called it a "bubble" and had some difficulty, though he did finally get a good alignment. Near the end of the moonwalk the announcer in Mission Control said, "The Lick Observatory in California reports a return on the laser experiment." With the Apollo 11 laser reflector a new era began in astrometry. The modern JPL lunar ephemerides are based entirely on range measurements to reflectors left on the Moon by American astronauts and Russian landers. The former methods of the transit instrument and lunar "theory" have been replaced by the laser and numerical integration, at least at JPL. I think lunar theory may still enjoy some vogue in France.