What SunMoonCalc is
SunMoonCalc is a set of astronomy calculators: sunrise and sunset for any date and location, golden hour and the three twilights around it, the moon phase for today and any other date, moonrise and moonset, the meteor shower calendar, and a set of city pages such as London, Chicago and Tokyo for people who want the answer without typing the coordinates in.
Every calculator runs in your browser. There is no account, no sign-up and no paywall, and the figures are produced on your own device rather than looked up on a server.
Why it exists
Most astronomy sites hand you a single number with no way to check it. That is fine for a quick glance, and useless when the number goes on a permit, a filming schedule or a plan that depends on the light being there.
So each tool here shows the formula it used, names the reference the formula comes from, and prints the intermediate values — declination, hour angle, altitude, illuminated fraction — instead of only the final time. If the answer looks wrong, you can find out why rather than being told to trust it.
How the numbers are produced
Solar positions come from the standard low-precision solar equations published by NOAA: the declination for the date, the hour angle at which the upper limb touches the 90.833° zenith (which folds in atmospheric refraction and the apparent radius of the sun), and your longitude converted to local clock time. Lunar phase figures use the published synodic-month and phase-fraction relationships. The yearly moon calendars and the meteor shower list use the same reference material.
Times are shown in the civil time of the time zone you select, and daylight saving is handled by the time zone rules rather than a fixed offset, so a date in the middle of a daylight-saving change is calculated day by day rather than shifted by a constant.
Typical accuracy
| Figure | Typical accuracy | Where it is weakest |
|---|---|---|
| Sunrise, sunset, solar noon | within about a minute | high latitudes, and dates near the seasonal extremes |
| Golden hour and twilight times | within a couple of minutes | the same, because the boundaries themselves are gradual |
| Moonrise, moonset | within a few minutes | the days around new moon, when the answer is near-meaningless anyway |
| Moon phase and illumination | a fraction of a percent | nowhere in particular; this is the most reliable figure on the site |
What this site does not do
- It is not a weather forecast. Cloud cover, rain and haze are not modelled here, and a clear calculation of a sunrise time tells you nothing about whether you will see it.
- In the polar regions the sun may not rise or set at all on a given date. The calculators report what the geometry gives rather than pretending there is an answer.
- It does not publish official tide tables, eclipse circumstances or almanac data. For anything with legal or safety weight, use the issuing authority.
- It is not a substitute for a measurement. If you need the real illumination at a specific window, meter it.
Who maintains it
SunMoonCalc is run by an independent developer. It is not a company, an observatory, an astronomical society or a licensed surveying practice, and nobody here holds a professional credential that is being used to lend these numbers authority. The site exists because the calculations are worth publishing plainly.
Figures change when the underlying reference or the method changes, and each page carries the date its figures were last checked. The editorial policy sets out exactly how that check is done, and contact is the fastest way to report something that looks wrong.
References and figures last reviewed: 28 October 2026.