You can check every number.
Nothing here is generated or approximated. These are the three claims the product rests on, and the links go to the sources.
- 0.03°
- The worst disagreement with the US Naval Observatory, measured across forty of their published reference events from 1920 to 2099.
- NASALRO
- The lunar surface is a real photograph, from the Lunar Reconnaissance Orbiter. NASA is credited as the source and does not endorse this product.
- Exact
- The lit area of every moon equals the fraction that was genuinely lit that day — proved by numerical integration, not picked from a set of stock phases.
Your moons
Each moon is a real date. Tap any moon for its phase and how much was lit.
Two ways to keep it
Post it, or print it
Most people make one for someone else — a 60th, a 70th, an 80th, a wedding anniversary, a first birthday, the day they met. A long span makes the most striking grid, because every year of it is on the page.
Free
A picture of your moons
- Phone-sized, yours to post or send
- No account, no email, no watermark
- The 19-year echo written on it
$14.99
$19
Save 21%
Launch price · $19 regular
A two-page portrait, ready to print and give
- Their name on it, and a line you write yourself
- Your milestones marked on the years they happened
- Page two names every moon — its date, its phase and how much was lit
- A4 and US Letter, both included
- Downloaded straight away · 14-day refund
Your printable portrait
Make it theirs
Everything below updates both pages as you type. What you approve here is exactly what the file prints.
The detail
About the moons
How they are computed, why they repeat, and what happens to your date.
They are real
Every phase here is computed from the positions of the sun and moon using the standard astronomical series in Jean Meeus's Astronomical Algorithms. The illuminated outline is calculated, not picked from a set of stock phases.
I check the result against the US Naval Observatory's published phase times. Across forty of their reference events between 1920 and 2099, the largest disagreement is 0.03°. The shaded part of each moon encloses exactly the fraction of the disc that was genuinely lit.
Photographic and Etched styles place that exact light shape over a local lunar surface derived from the NASA Scientific Visualization Studio CGI Moon Kit and Lunar Reconnaissance Orbiter data. NASA is acknowledged as the source and does not endorse this product.
The 19-year echo
235 lunar months come to almost exactly 19 years. Astronomers call it the Metonic cycle, and it means the moon on the 19th anniversary of any date looks nearly the same as it did on the day itself — then again at 38, and 57.
Across 355 sample birthdates the phase came back within 3.6 percentage points on average. You can see it in your own grid.
Printing it
Warm Observatory is built for a home printer: light paper, not much ink. Print at 100% (not "fit to page"), and leave the margins alone — every home printer has an edge it physically cannot reach.
Type and phase geometry remain vector-sharp. The committed lunar surface is high resolution enough for the moon sizes in the included A4 and US Letter files.
What I keep
Not your date. No accounts, no cookies, no advertising trackers. Your date becomes moons inside your own browser; it only reaches my server if you buy the printable portrait, and then only to draw the file.
I do count anonymous totals — how many portraits were made today, how many cards saved — with no way to tell who did what. Exactly what that means.