Daylight, twilight and lunar phases

Select the location and date before reading the sun times. Results use that city's time zone, including its daylight-saving offset for the date. Solar noon is when the sun reaches its highest daily position; it need not be 12:00 on the clock.

Day length is the interval between sunrise and sunset. If sunrise is 07:30 and sunset is 17:00, that gives about nine and a half hours of daylight. Twilight extends beyond those times, so sunset does not mean the sky becomes completely dark at once. Civil, nautical and astronomical twilight use progressively lower positions of the sun below the horizon.

Moon illumination describes how much of the lunar disc is lit as viewed from Earth. A half-lit moon can be waxing towards full or waning towards new; use the phase name as well as the percentage. Illumination alone does not tell you whether the moon will be above your horizon, or whether clouds will hide it.

Use the lunar calendar to compare nearby dates and the season times for approximate equinox and solstice instants. The same astronomical event happens worldwide, but its local clock time and even its calendar date depend on the selected city. The northern and southern hemispheres experience opposite seasons.

Everything on this page is computed in your browser rather than fetched from a service. The sun times come from the standard sunrise equation, anchored to local noon on the chosen day so that the calculation cannot slip onto a neighbouring date at the edges of a time zone. Sunrise and sunset are the moments the centre of the sun sits 0.833° below the true horizon, a figure that allows both for the radius of the solar disc and for average atmospheric refraction, which is why the sun appears to rise slightly before it geometrically does. Civil dawn and civil dusk use 6° below the horizon, the point at which there is generally enough light to read outdoors without a lamp.

The method is good to roughly a minute for sun events at moderate latitudes. Two things erode that. Close to the poles the sun crosses the horizon at a very shallow angle, so a small error in altitude turns into a large error in time. Nearer home, the calculation assumes a flat sea-level horizon at a single point: a ridge to the east, a row of buildings, or a few hundred metres of altitude can move the sunrise you actually see by many minutes, in either direction. Refraction also varies with air temperature and pressure, and the 0.833° allowance is an average rather than tonight's value.

Coordinates are printed under the location so you can judge how well the chosen city stands in for where you are. They are a single point near each city centre, quoted to four decimal places. Longitude is what shifts sun times most within a country: a degree of longitude is four minutes of solar time, so two cities sharing a time zone and a clock can have sunrises half an hour apart.

The bar under the sun figures is one full day, midnight to midnight, in the selected city's zone, with the amber band marking daylight and the violet bands on either side marking civil twilight. Its value is comparative: step through a few days with the Prev and Next buttons and the amber band visibly grows or shrinks, and step through a few months and it slides sideways as well, which is the part a table of times hides.

Under "Day length" is the change against the previous day, and it is worth watching rather than the day length itself. Near an equinox at middle latitudes it reads a few minutes a day, so the evenings noticeably draw in or out from one week to the next. Within a few days of a solstice it falls to a minute or to nothing at all, which is where the word comes from: sol plus sistere, the sun standing still. A city near the equator shows a figure close to zero all year.

Above roughly 66.5° of latitude the sun can stay up or down for a whole day. An amber note then says midnight sun or polar night, the day length reads 24h 00m or 0h 00m, and the sunrise and sunset fields have nothing to show because no such event happens. Civil dawn and dusk can be missing on their own at lower latitudes too: through midsummer in southern Scandinavia, Scotland or southern Alaska the sun never drops the full 6° below the horizon, twilight lasts all night, and the two fields have no crossing to report.

The moon panel gives the phase name, the illuminated fraction of the disc as seen from Earth, and the age of the moon in days through a cycle that averages 29.53 days. The four dates listed under it are the next new moon, first quarter, full moon and last quarter, each located to within a minute and shown in the selected city's zone.

The month grid at the foot of the page works differently, and the difference catches people out. Each square is the phase at 12:00 UTC on that day, and the pills under the grid label the principal phases in UTC as well. A full moon falling at 00:40 UTC is therefore the 3rd in the grid but can be listed as the evening of the 2nd in the phase list higher up, when you are reading a city several hours behind UTC. Neither is wrong; they are the same instant told in two different zones.

The grid opens on the month of the date you selected and then keeps its own position once you use its arrows, so you can browse ahead without disturbing the sun figures above. There are no moonrise and moonset times here: the page tells you what shape the moon is and when it changes, not when it will be above your horizon.