August 18, 2026 · London
London today (August 18, 2026): the time below is when civil twilight ends and it starts to feel dark. Sunset, nautical and astronomical twilight are shown too — all calculated for London's coordinates.
It doesn't get dark at a single instant at sunset — darkness falls gradually as the sun sinks further below the horizon. The time between sunset and true darkness is called twilight, and it is split into three phases. The times above are calculated for the reference city today; use “Use my location” for precise times for your own spot.
Astronomers divide twilight by how far the sun is below the horizon:
In the UK it typically takes 30–60 minutes after sunset for civil twilight to end and for it to feel dark. The further north you go and the closer to the summer solstice, the longer twilight lasts. Around midsummer in northern Britain it never becomes astronomically dark — the sun doesn't reach 18° below the horizon, and the sky stays faintly lit all night.
In winter it happens faster: the sun dives steeply below the horizon, so less time passes from sunset to full darkness. See also when is it lightest and the year chart for how light changes through the year.
The single thing that determines how long dusk drags on is the angle at which the sun crosses the horizon. Near the equator it drops almost straight down, so it passes through each twilight band quickly. At high latitudes it slides sideways along the horizon at a shallow angle, taking far longer to sink the same number of degrees.
As a rough guide for the time from sunset to the end of civil twilight — the point at which it starts to feel dark:
Note that the seasonal pattern is not the one most people assume, and it is not a simple summer-versus-winter split either. Twilight is shortest at the equinoxes and longer at both solstices. The reason is the angle of the sun's path: at the equinox the sun rises due east and sets due west, crossing the horizon at the steepest angle it ever manages for that latitude, so it plunges through each twilight band. At either solstice its path is tilted further from vertical and it sinks more slowly.
The two solstices are not symmetrical, though. Midsummer twilight is much the longer of the two — 61 minutes against 47 in Copenhagen — because in June the sun is also travelling almost parallel to the horizon at its lowest point. Long, lingering dusks really are a summer phenomenon; it is the equinox, not midwinter, that gives the abrupt ones.
North of about 48–49° latitude — which includes all of Britain, Denmark, and most of northern Europe — there is a stretch of summer during which the sun never reaches 18° below the horizon. Astronomical twilight simply does not end; the previous evening's dusk runs into the next morning's dawn without a gap.
Push further north, past roughly 60°, and the same happens with nautical twilight: the sky stays bright enough all night to make out the horizon. This is what St Petersburg means by its white nights. North of the Arctic Circle it goes further still and the sun does not set at all — the midnight sun, which our page on when it is lightest covers.
The practical upshot for anyone who looks at the sky: there is a window of roughly mid-May to late July across northern Europe when properly dark astronomical observing is impossible regardless of the weather. Deep-sky astronomy in those latitudes is a winter activity by necessity.
The blue hour is the earlier part of civil twilight, when the sun is roughly 4–6° below the horizon. The direct light is gone but the upper atmosphere is still lit, and because the longer wavelengths have been scattered out of the path, what reaches the ground is heavily weighted towards blue. It is the short window in which artificial lighting and the sky are close enough in brightness to expose for both at once — which is why almost every good photograph of a city at night is actually a photograph taken during the blue hour.
It is the mirror image of the golden hour, the period just after sunrise and before sunset when the sun is low but still up, and its light passes through so much atmosphere that it arrives warm and soft. Both are governed purely by the sun's altitude, so both are predictable exactly. At the latitudes where twilight is long, both last longer too — a northern summer gives you a generous golden hour, while a tropical one gives you a few minutes.
Different activities use different thresholds, which is why there is no single answer to when it gets dark:
Whichever definition you need, the exact times for your own coordinates are on this page. For the underlying definitions and how they are computed, see how we calculate the times, and for the wider picture of how all of this shifts across the year, what day length is.
It starts to feel dark when civil twilight ends — the time shown at the top of the page for the reference city. Use “Use my location” for your own spot.
At sunset the sun drops below the horizon, but it is still light. Only once the sun is at least 6° below the horizon (civil twilight ends) does it begin to get dark.
Close to the summer solstice the sun doesn't reach 18° below the horizon at night in much of the UK, so astronomical darkness is never reached and the sky stays faintly lit.