Methodology and sources
This page explains how the guides and the game are built, so you can check them. It covers where the numbers come from, what the instruments simplify and how a round is scored.
How we handle sources
Each guide lists its sources at the end, with the link and the day we opened them. We read the page ourselves before we cite it. A guide needs at least two official sources, and when two disagree the guide says so. The full rules are in the Editorial policy.
Numbers the instruments use
Every instrument is drawn by calculation in your browser. There are no stock pictures. These are the published values behind the calculations.
| Value | Used for | Source |
|---|---|---|
| Moon's cycle of phases, 29.53 days | Moon Dial, Rise & Set Dial | NASA Moon Fact Sheet |
| Moon's trip around Earth against the stars, 27.3217 days | Clock Dial | NASA Moon Fact Sheet |
| Moon's distance, 363,300 km at its closest and 405,500 km at its farthest | Alignment Bench | NASA Moon Fact Sheet |
| Moon's radius, 1,737.4 km, and the tilt of its orbit, 5.145 degrees | Alignment Bench | NASA Moon Fact Sheet |
| Sun's radius, 695,700 km | Alignment Bench | NASA Sun Fact Sheet |
| Earth's equatorial radius, 6,378.137 km, and the tilt of its axis, 23.44 degrees | Alignment Bench, Orbit Dial | NASA Earth Fact Sheet |
| Earth's distance from the Sun, from 147.095 to 152.100 million km | Orbit Dial | NASA Earth Fact Sheet |
| The Sun's position through the year | Orbit Dial, Clock Dial | U.S. Naval Observatory, Approximate Solar Coordinates |
The guides use more numbers, such as the length of the tropical year or the sidereal day. Each one is sourced in the guide where it appears.
What the instruments simplify
- Moon Dial. The Moon's orbit is drawn as a circle around Earth. The Moon Dial shows the phase and the view from each hemisphere.
- Alignment Bench. The side view stretches heights and squeezes distances so shadows can be seen. Shadow sizes come from the radii and distances above. The Moon is set at its closest, its farthest or its average distance. The eclipse limits come from the geometry, and each guide compares them with the figures NASA publishes.
- Orbit Dial. The calendar is the year 2026. Day length and the Sun's noon height use the geometric horizon. Real sunrise and sunset tables add about 50 arcminutes for the Sun's size and the bending of light, so their daylight lasts a little longer.
- Clock Dial. Each dial shows one question. The time zone dial shows whole and fractional hour offsets. The leap year dial uses the Gregorian rule.
- Rise & Set Dial. It describes one place, at 40 degrees north, near an equinox. The Moon rises about 49 minutes later each day in this model, which follows from the 29.53-day cycle. NASA gives "about 50 minutes" on average.
None of the instruments calculates exact times or dates for a place. For those, use official tables.
How a round works
- You choose a level: Bronze, Silver or Gold. A request appears, and you turn the dial and press "Lock it in".
- A match is a setting inside the window for that level. The window shrinks from Bronze to Gold. Each window sits inside the one before it.
- Bronze shows names on the instrument and allows 2 mistakes. Silver shows numbers and tick marks only and allows 2 mistakes. Gold shows no marks and allows 1 mistake.
- The base score is 100, 200 or 300. Each mistake costs 15 points, and each use of "Show the zone" costs 10. The lowest score for a win is 10.
- Rounds are drawn with the browser's random number generator. The game prefers entries you have not won at that level and avoids the last ten you played.
- There is no timer and no daily limit.
How we check the instruments
Before publishing, we test each instrument against values from official sources, such as the length of the lunar cycle, the tilt of the axis, the dates of the 2026 solstices and equinoxes in the U.S. Naval Observatory table, the date of perihelion and the noon height of the Sun at 30 degrees north on the March equinox. We also check that each request has one right answer: the settings that match form a single range, not two separate ones.
Sources
- NASA Space Science Data Coordinated Archive, "Moon Fact Sheet": nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html. Opened November 10, 2026.
- NASA Space Science Data Coordinated Archive, "Sun Fact Sheet": nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html. Opened November 10, 2026.
- NASA Space Science Data Coordinated Archive, "Earth Fact Sheet": nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html. Opened November 10, 2026.
- U.S. Naval Observatory, "Computing Approximate Solar Coordinates": aa.usno.navy.mil/faq/sun_approx. Opened November 10, 2026.