Context

Time considerations on the moon are a highly technical and complex context that need not be detailed here at length. The basics are that a lunar day (e.g. a rotation, sunrise to sunrise) lasts approximately 27-28 days. This means that daylight at a given landing site lasts approximately 14 days, and time from sunrise to high noon is approximately 7. For various thermal and navigational reasons, our estimated landing time for the 2019 launch is in the morning around Day 4-5. It's unlikely that a rover our size will operate through the heat of noon, but even if it did, the afternoon would be symmetric for these purposes. As such, my clock need only cover three 24-hour Earth days.

The key factor we care about--and the key one I want to make intuitive--for planning lunar rover missions is the position of the sun overhead on the moon with respect to our time on Earth. As such, I've decided that my clock will show the position of the sun (or the portions of dark and light) throughout this morning-to-noon timeframe and relate it to a 24-hour Earth day.

Showing the continuous position of the sun throughout three 24-hour Earth days amounts to a spiral shape around the clock face. I've decided to buy a 24-hour clock kit from Amazon at my own expense as this simplifies both the physical clock face and the intuition for fellow scientists reading it. The sketch below shows my basic concept, which includes four parts. The clock face itself has no numbers, as this would only confuse the issue of extraterrestrial time. The spiral is constructed actually of two different spirals, a dark one and a light one (the latter representing the sun), and the ratio between them shifts from mostly dark to 50/50 as the spiral continues outward. The clock hand, of which there is only one (minutes and seconds don't matter much in this case), includes three windows through which to view the spiral. If you're on Mission Day 1, you check the first window, for Day 2, the second, etc. This allows quick comparison between Earth days as is important for developing lunar intuition. Providing four windows would be more accurate to our mission profile, but three is an innately absorbable number for humans to view.