Comparisons of of Astro.sunrise/3, Astro.sunset/3, Astro.moonrise/3,
and Astro.moonset/3 against Skyfield (JPL DE440s), USNO (DE430),
and timeanddate.com were run to confirm accuracy.
Sunrise / Sunset
Both Astro and Skyfield use JPL DE440s ephemerides, which explains their near-exact agreement. The timeanddate.com data (used in the CSV test files) agrees with both to within ±1 minute, with the 2 boundary cases at 61 seconds being a minute-rounding artefact.
The comparison uses test dates from December 2019 across 5 cities (Sydney, Moscow, NYC, São Paulo, Beijing) for a total of 310 comparisons.
Overall
| Comparison | Max diff | Mean diff | Within ±1 min |
|---|---|---|---|
| Astro vs Skyfield | 7 s | 3.8 s | 310/310 (100%) |
| Astro vs timeanddate.com (CSV) | 61 s | ~29 s | 308/310 (99.4%) |
| timeanddate.com vs Skyfield | 61 s | 28.5 s | 308/310 (99.4%) |
Per-city (Astro vs Skyfield)
| City | Rise max | Rise avg | Set max | Set avg |
|---|---|---|---|---|
| Sydney | 4 s | 2.8 s | 7 s | 4.9 s |
| Moscow | 5 s | 3.1 s | 6 s | 4.7 s |
| NYC | 5 s | 3.2 s | 6 s | 4.5 s |
| São Paulo | 4 s | 3.0 s | 6 s | 4.6 s |
| Beijing | 5 s | 3.3 s | 6 s | 4.3 s |
Moonrise / Moonset
The ~16 s mean difference against USNO is explained by two factors: USNO uses DE430 (vs the JPL DE440s that Astro uses), and USNO rounds to the nearest minute. Skyfield shows the same ~16 s offset against USNO, suggesting this is an ephemeris version difference rather than an algorithmic error.
The comparison uses test dates from March 2026 across 4 cities (NYC, London, Sydney, Tokyo) for a total of 70 comparisons.
Overall
| Comparison | Max diff | Mean diff | Within ±1 min |
|---|---|---|---|
| Astro vs Skyfield | 6 s | 2.5 s | 240/240 (100%) |
| Astro vs USNO | 32 s | 15.5 s | 67/67 (100%) |
| Skyfield vs USNO | 35 s | 15.6 s | 67/67 (100%) |
Per-city (Astro vs Skyfield)
| City | Max diff | Avg diff |
|---|---|---|
| NYC | 5 s | 2.1 s |
| London | 6 s | 2.8 s |
| Sydney | 6 s | 3.2 s |
| Tokyo | 5 s | 2.1 s |
Per-city (Astro vs USNO)
| City | Max diff | Avg diff |
|---|---|---|
| NYC | 32 s | 16.3 s |
| London | 30 s | 16.4 s |
| Sydney | 28 s | 11.8 s |
| Tokyo | 28 s | 17.7 s |