Methodology and accuracy
Every time, position and phase on this site is computed by our own build from a numerical ephemeris; nothing is copied from another site's tables. The build runs every night and repeats the accuracy check below; if too many checks fail, the new build is not published.
Accuracy check: 45 of 45 within tolerance
Our computed values against published references: the U.S. Naval Observatory's Astronomical Applications service (sunrise, sunset, moonrise, moonset, phases, local eclipse circumstances), NASA's eclipse tables (Fred Espenak, NASA GSFC) and Fred Espenak's planetary phenomena tables. The cases include the tropics, the southern hemisphere, a sub-Arctic midsummer and polar night. Over all 99 principal Moon phases of 2027–2028, the largest difference from USNO is 39 seconds (mean 16 s); USNO gives phases to the minute.
| Event | Where / when | Reference | Ásar bardagi | Difference | |
|---|---|---|---|---|---|
| Sunrise | New York, 2027-03-20 | 11:00 UTC | 10:59:42 UTC | -18 s | ✓ USNO rounds to the minute |
| Sunset | New York, 2027-03-20 | 23:08 UTC | 23:07:57 UTC | -3 s | ✓ USNO rounds to the minute |
| Sunrise | London, 2027-06-21 | 03:43 UTC | 03:43:03 UTC | +3 s | ✓ USNO rounds to the minute |
| Sunset | London, 2027-06-21 | 20:21 UTC | 20:21:30 UTC | +30 s | ✓ USNO rounds to the minute |
| Sunrise | Sydney, 2027-12-21 | 18:41 UTC | 18:40:59 UTC | -1 s | ✓ USNO rounds to the minute |
| Sunset | Sydney, 2027-12-21 | 09:05 UTC | 09:05:15 UTC | +15 s | ✓ USNO rounds to the minute |
| Sunrise | Singapore, 2027-01-15 | 23:13 UTC | 23:12:43 UTC | -17 s | ✓ USNO rounds to the minute |
| Sunset | Singapore, 2027-01-15 | 11:16 UTC | 11:15:30 UTC | -30 s | ✓ USNO rounds to the minute |
| Sunrise | Reykjavík, 2027-06-10 | 03:04 UTC | 03:04:16 UTC | +16 s | ✓ USNO rounds to the minute |
| Sunset | Reykjavík, 2027-06-10 | 23:52 UTC | 23:51:44 UTC | -16 s | ✓ USNO rounds to the minute |
| Sunrise | Tromsø, 2027-01-05 | Object continuously below the Horizon | none | — | ✓ |
| Sunset | Tromsø, 2027-01-05 | Object continuously below the Horizon | none | — | ✓ |
| Moonrise | Cape Town, 2027-02-20 | 17:18 UTC | 17:17:33 UTC | -27 s | ✓ USNO rounds to the minute |
| Moonset | Cape Town, 2027-02-20 | 03:34 UTC | 03:33:58 UTC | -2 s | ✓ USNO rounds to the minute |
| Moonrise | Tokyo, 2027-05-10 | 23:46 UTC | 23:45:46 UTC | -14 s | ✓ USNO rounds to the minute |
| Moonset | Tokyo, 2027-05-10 | 13:53 UTC | 13:52:58 UTC | -2 s | ✓ USNO rounds to the minute |
| New Moon | 2027-03-08 | 09:29 UTC | 09:29:28 UTC | +28 s | ✓ |
| First Quarter | 2027-03-15 | 16:25 UTC | 16:25:12 UTC | +12 s | ✓ |
| Full Moon | 2027-03-22 | 10:44 UTC | 10:43:47 UTC | -13 s | ✓ |
| Last Quarter | 2027-03-30 | 00:54 UTC | 00:53:56 UTC | -4 s | ✓ |
| Annular solar eclipse | 2026-02-17 | 12:13:05 TD, annular, mag 0.963 | 12:13:06 TT, annular, mag 0.964 | +1 s | ✓ NASA greatest eclipse |
| Total lunar eclipse | 2026-03-03 | 11:34:52 TD, total, mag 1.151 | 11:34:51 TT, total, mag 1.149 | -1 s | ✓ NASA greatest eclipse |
| Total solar eclipse | 2026-08-12 | 17:47:05 TD, total, mag 1.039 | 17:47:06 TT, total, mag 1.039 | +1 s | ✓ NASA greatest eclipse |
| Partial lunar eclipse | 2026-08-28 | 04:14:04 TD, partial, mag 0.930 | 04:14:03 TT, partial, mag 0.929 | -1 s | ✓ NASA greatest eclipse |
| Annular solar eclipse | 2027-02-06 | 16:00:47 TD, annular, mag 0.928 | 16:00:47 TT, annular, mag 0.928 | +0 s | ✓ NASA greatest eclipse |
| Penumbral lunar eclipse | 2027-02-20 | 23:14:06 TD, penumbral, mag -0.057 | 23:14:04 TT, penumbral, mag -0.059 | -2 s | ✓ NASA greatest eclipse |
| Penumbral lunar eclipse | 2027-07-18 | 16:04:09 TD, penumbral, mag -1.068 | 16:04:09 TT, penumbral, mag -1.068 | -0 s | ✓ NASA greatest eclipse |
| Total solar eclipse | 2027-08-02 | 10:07:49 TD, total, mag 1.079 | 10:07:51 TT, total, mag 1.080 | +2 s | ✓ NASA greatest eclipse |
| Penumbral lunar eclipse | 2027-08-17 | 07:14:59 TD, penumbral, mag -0.525 | 07:14:56 TT, penumbral, mag -0.527 | -3 s | ✓ NASA greatest eclipse |
| Partial lunar eclipse | 2028-01-12 | 04:14:13 TD, partial, mag 0.066 | 04:14:12 TT, partial, mag 0.067 | -1 s | ✓ NASA greatest eclipse |
| Annular solar eclipse | 2028-01-26 | 15:08:58 TD, annular, mag 0.921 | 15:08:59 TT, annular, mag 0.921 | +1 s | ✓ NASA greatest eclipse |
| Partial lunar eclipse | 2028-07-06 | 18:20:57 TD, partial, mag 0.389 | 18:20:56 TT, partial, mag 0.390 | -1 s | ✓ NASA greatest eclipse |
| Total solar eclipse | 2028-07-22 | 02:56:39 TD, total, mag 1.056 | 02:56:39 TT, total, mag 1.056 | +0 s | ✓ NASA greatest eclipse |
| Total lunar eclipse | 2028-12-31 | 16:53:15 TD, total, mag 1.246 | 16:53:14 TT, total, mag 1.247 | -1 s | ✓ NASA greatest eclipse |
| Solar eclipse, eclipse begins | Dallas, 2024-04-08 | 17:23:14.7 UTC | 17:23:20 UTC | +6 s | ✓ USNO to 0.1 s; ours to the second |
| Solar eclipse, maximum eclipse | Dallas, 2024-04-08 | 18:42:32.9 UTC | 18:42:39 UTC | +7 s | ✓ USNO to 0.1 s; ours to the second |
| Solar eclipse, eclipse ends | Dallas, 2024-04-08 | 20:02:35.5 UTC | 20:02:41 UTC | +6 s | ✓ USNO to 0.1 s; ours to the second |
| Solar eclipse, magnitude | Dallas, 2024-04-08 | 1.015 | 1.014 | — | ✓ |
| Jupiter opposition | 2026-01-10 | 08h UTC | 08:42 UTC | +42.1 min | ✓ reference gives the hour (00–59 min) |
| Saturn opposition | 2026-10-04 | 12h UTC | 12:29 UTC | +29.2 min | ✓ reference gives the hour (00–59 min) |
| Jupiter opposition | 2027-02-11 | 00h UTC | 00:28 UTC | +28.8 min | ✓ reference gives the hour (00–59 min) |
| Mars opposition | 2027-02-19 | 15h UTC | 15:50 UTC | +50.9 min | ✓ reference gives the hour (00–59 min) |
| Saturn opposition | 2027-10-18 | 00h UTC | 00:35 UTC | +35.5 min | ✓ reference gives the hour (00–59 min) |
| Venus greatest elongation | 2027-01-03 | 19h UTC, 47.0° | 17:58 UTC, 47.0° | -1.0 h | ✓ reference gives the hour; greatest elongation is a very flat maximum |
| Venus inferior conjunction | 2026-10-24 | 03h UTC | 03:44 UTC | +44.1 min | ✓ reference gives the hour (00–59 min) |
Sun and Moon rise and set references are rounded to the minute, so differences up to 30 s are rounding. Rise and set times also depend on atmospheric refraction, which varies with the weather by a minute or more near the horizon, and on your local horizon; no almanac can do better than that. References fetched 2026-10-26.
How it is computed
- Positions of the Sun, Moon and planets: JPL's DE421 planetary ephemeris (NASA Jet Propulsion Laboratory, public domain), evaluated with the Skyfield library (MIT licence), including light time, aberration and nutation, for an observer at the city's coordinates at sea level.
- Sunrise and sunset: the moment the top of the Sun touches the horizon with standard refraction (centre 0.8333° below the horizon), the convention used by almanacs. Twilights: Sun 6° (civil), 12° (nautical) and 18° (astronomical) below the horizon. "Dark" means astronomical darkness.
- Moonrise and moonset: the Moon's upper limb on the horizon, with refraction and parallax for the observer's position.
- Planet visibility: a naked-eye planet counts as visible when it is at least 5° above the horizon while the Sun is at least 6° below; Uranus and Neptune need 15° and a Sun 15° down. Checked every 5 minutes through the night. Magnitudes from the formulae of Mallama and Hilton (2018).
- Constellations: the official IAU boundaries (Roman 1987), as packaged with Skyfield.
- Moon phases and events: principal phases are the instants the Moon's ecliptic longitude is 0°, 90°, 180° and 270° from the Sun's. Perigee and apogee are distance extremes. Close approaches are geocentric separations under 3° (planets at least 12° from the Sun).
- Eclipses: lunar eclipses with Skyfield's eclipse search (Explanatory Supplement method, Danjon shadow enlargement), contact times from the same geometry at one-minute steps. Solar eclipses by our own search at each new Moon: greatest eclipse is the minimum distance of the Moon's shadow axis from Earth's centre, the type comes from the umbral cone at Earth's surface, and local circumstances are computed from topocentric Sun and Moon positions every minute.
- Meteor showers: peak instants are when the Sun reaches the solar longitude (J2000) listed for each shower in the International Meteor Organization's 2026 working list; activity periods, radiants, speeds and ZHRs come from the same list. Descriptions are written by us.
- ISS passes: SGP4 propagation (Skyfield) of the latest orbital elements from CelesTrak, fetched once a day. A pass is listed when the station is at least 10° up, in sunlight, while the observer's Sun is more than 6° below the horizon. Elements older than three days are not used.
- Sky charts: stars to magnitude 4.6 (5.0 in the interactive version) from the Hipparcos catalogue (ESA), constellation figures and the Milky Way outline from d3-celestial by Olaf Frohn (BSD 3-Clause licence), drawn in a stereographic projection centred on the zenith.
- In your browser: "Use my location", the bright-star helper, the Moon widget and the time slider on the charts use Astronomy Engine by Don Cross (MIT licence), served from this site. It agrees with the server-side calculation to well within a minute for rise and set times.
- Time zones: IANA time zone database via Python's zoneinfo; local times include daylight-saving changes.
What we don't do
- No weather or cloud forecast: a clear-sky prediction would need a commercial data licence we don't have.
- No light-pollution maps. Rates for meteors are upper guides for a dark site.
- Elevation is ignored (sea level); from a mountain the horizon is lower and the Sun sets later by a few minutes.
Sources and licences
- JPL DE421 ephemeris: NASA/JPL, public domain (US Government work).
- Skyfield: Brandon Rhodes, MIT licence. Astronomy Engine: Don Cross, MIT licence.
- Star catalogue: ESA Hipparcos, via d3-celestial (Olaf Frohn, BSD 3-Clause licence), which also supplies constellation figures and the Milky Way outline.
- Meteor shower data: International Meteor Organization, Meteor Shower Calendar 2026, Table 5 (facts only).
- Eclipse reference tables: NASA Goddard Space Flight Center, Fred Espenak, public domain.
- Validation references: U.S. Naval Observatory Astronomical Applications Department (public domain); Fred Espenak, AstroPixels (facts used as a check only).
- ISS orbital elements: CelesTrak (Dr T.S. Kelso), fetched in line with its usage policy.
- Photographs: Wikimedia Commons, each credited with author and licence beside the image.
- Illustrations, charts, diagrams and text: original to this site.