Method
How we know
Every figure on these pages is either computed from an open library, taken from a named agency, or marked as our own choice. This page lists the checks that were run and the gaps.
Checks run when the pages were built
| What | Result |
|---|---|
| Moon phases | 99 phases in 2026 and 2027 compared with the US Naval Observatory table. Largest difference 79 seconds. |
| Equinoxes and solstices | 8 events compared. Largest difference 60 seconds. |
| Solar eclipses | 4 eclipses compared by date and type. All match. |
| Sunrise and sunset | 20 times on both 2026 solstices at six cities compared. Largest difference 30 seconds. |
| Constellations | The 88 areas add up to the whole sky. The three largest are Hydra, Virgo and Ursa Major. Points along every boundary were checked against the astronomy library: one side inside the constellation and the other not. |
| Star names | All 331 named stars in the catalogue agree with the IAU list on position and constellation. |
A claim appears on a page only if its check ran in this build. If the comparison tables are missing the claim is left out instead of assumed.
What is our own choice
- Darkness here means the Sun is more than 18 degrees below the horizon.
- The best month for a constellation is when its middle is highest at 9 pm local solar time.
- Distances to asteroids are shown as multiples of the Moon's distance, and sizes use an assumed reflectivity of 13 percent.
- Passes of satellites need to rise at least 10 degrees.
- Low-confidence fire detections are left out and the rest are grouped into quarter-degree cells.
What we could not confirm
- The exact latency of NASA's fire files. NASA says usually within three hours; we measured about two and a half.
- The licence on the IAU's constellation boundary text files. The IAU states Creative Commons Attribution for its charts.
- How fast satellite predictions drift, from a primary source.
- The IAU star name list is dated 2022-04-04. A newer one may exist.
Live data
The live app is not forecast by us. It shows what the agencies publish with their times, and the Data status screen in the app shows when each feed was last updated.
The code and data notes are on GitHub.
Sources
- astronomy-engine. The MIT licensed library that does the calculations, run on the page's build machine and in the app
- U.S. Naval Observatory, Astronomical Applications API. The published tables our results were compared with
- IAU. Constellations and star names
- NWS disclaimer and public domain statement. The terms for using NOAA and NWS information