How SkyWatch is built
Every number on this site is computed here, from published algorithms. Nothing is scraped from another sun-times site, and there is no API behind it.
Computed from standard astronomical algorithms · Reviewed Oct 2026 · Method
The algorithms
Solar position follows Jean Meeus, Astronomical Algorithms (2nd ed.), chapter 25 — the same equations behind the NOAA solar calculator. Lunar position uses the principal terms of the ch. 47 series; illumination and phase follow ch. 48. Sidereal time is ch. 12. The mathematics is public domain; no licence attaches to it, which is why this site has no attribution requirement for its numbers and no upstream that can withdraw them.
How events are found
Rather than the closed-form hour-angle formula, the altitude of the Sun or Moon is sampled across the local day and the threshold crossings are found by interpolation. That gives identical treatment to sunrise, every twilight and the Moon, and it returns an honest blank where an event genuinely does not occur, instead of a nonsense value.
Sunrise and sunset use the conventional −0.833° for the Sun's centre, which allows 34 arcminutes of refraction and 16 for the Sun's own radius. The Moon uses Meeus's standard altitude, 0.7275π − 0.5667°, which already accounts for parallax — applying a parallax correction on top of it is a real and easy mistake, and it puts moonrise about five minutes out.
Accuracy, honestly
Checked against the US Naval Observatory almanac, solar times agree to within a minute and lunar times to within about a minute. Those checks run as a test on every build. The truncated lunar series is worth roughly a minute on its own, so times are quoted to the minute and never to the second.
The larger error is not in the arithmetic. Refraction depends on temperature and pressure, and the standard allowance can be a minute or two off on a cold clear morning. And the local horizon dominates everything: a hill to your west can take half an hour off sunset. Treat these as sea-level, flat-horizon figures.
Places
192 places. Coastal positions are the 76 LINZ standard tide ports, which keep their surveyed coordinates. Inland towns are centroids derived from OpenStreetMap features assigned to each locality, accurate to about a kilometre — worth a few seconds of sunrise time, well inside the published precision. Coordinates are rounded to three decimal places for that reason.
What is excluded, and why
The Chatham Islands are not included. They keep their own time zone, 45 minutes ahead of the rest of the country, and publishing their times under NZST would be wrong by exactly that much on every page — plausible, consistent and wrong. Raoul Island and Scott Base are out for the same class of reason. Seven LINZ tide ports carry no coordinates in the source data; a tide prediction does not need a position but a sunrise does, so they have tide pages and no sky page.
No live data
SkyWatch publishes nothing that changes in real time. There is no live aurora forecast, no cloud cover and no "is it visible right now". Those require an observation feed, and a static page that implied it had one would be lying. Where live data is the right answer — the aurora especially — the site links to the source rather than repackaging it.