As we eagerly awaited the arrival of Voyager 2 at Neptune’s influence boundary, we decided to make things more exciting by organizing a prediction pool among the science teams at Jet Propulsion Laboratory. We used a chalkboard to record our entries based on when the spacecraft would encounter the “bow shock” of Neptune’s magnetosphere in PDT-ERT (Pacific Daylight Time-Earth Received Time).
There were only five predictions to choose from, all falling on Day of Year 235, which corresponds to August 23rd in non-leap years. The one-way light time from the spacecraft was 4 hours and 6 minutes, and the spacecraft event time (SCET) was typically given in Greenwich Mean Time (GMT). To convert from PDT-ERT to GMT-SCET, we had to add 7 hours and then subtract 4 hours and 6 minutes, resulting in a difference of 2 hours and 54 minutes.
My prediction was set for 12 noon on DOY 236, which was August 24th at 1454 GMT-SCET. However, much to my surprise, the Plasma Science experiment actually detected the bow shock on August 24th at precisely that same hour and minute – coming very close indeed! What really stood out about this whole ordeal was not just the accuracy of my prediction but also the fact that there is documentation of this prediction pool and even a photo capturing the event still exists today.