When night never falls: the summer nights without true darkness, from Bucharest to Edinburgh
Edinburgh: 96 nights a year that never get fully dark. Bucharest: none.
In summer, on 96 nights of the year, the Sun over Edinburgh never gets 18 degrees below the horizon, the depth at which astronomers count night as complete. Over Bucharest, in Romania, it gets there every night. The parallel between them, 48.56°N, runs 33 km north of Romania’s northernmost point. And 160 sky meters across Europe show where the difference really shows in the sky: only further north, where the Sun stays closer to the horizon.
away from city lights
away from city lights
The night of 21 June
The northern sky on the same night, at its darkest moment, away from city lights. The stars are real; the sky’s glow follows the sky-meter measurements.
Astronomers count night as complete once the Sun is 18 degrees below the horizon. Above that, the high air still catches its light and scatters some of it down: this is astronomical twilight, too faint to notice in a town, strong enough to hide the faintest stars.
At midnight the Sun sits below the northern horizon. How far down it gets depends on two things: how far you are from the pole, and how high the Sun climbs in that season. At the summer solstice the sum is simple: 90 degrees, minus your latitude, minus 23.44. With 18 degrees left over, the line falls at 48.56°N.
June brighterno difference
Paris lies just north of it and loses true night on 18 nights, from 12 June to 29 June. Vienna lies just south and keeps it, with 64 minutes of darkness on the shortest night. Romania’s northernmost point, at Horodiștea in Botoșani county, is at 48.27°N: 33 km too far south. There, on the solstice night, the Sun sinks to 18.3 degrees and true darkness lasts 58 minutes.
The map follows the date chosen above: the paler zone in the north is where, on that night, the Sun no longer reaches 18 degrees. The dots are the sky meters of the next chapter. Click the map to put any place in the right-hand window.
What the sky meters show: the lost night only shows further north#
The sum says where the Sun no longer reaches 18 degrees. It does not say whether the sky looks any different. That can be measured: Europe’s STARS4ALL network runs small meters pointed at the zenith that log the sky’s brightness every minute. For June and December of 2024 and 2025, 160 meters in 16 countries have enough moonless nights to compare a summer midnight with a winter one.
The result follows the Sun’s depth, not the line on the map. Where the Sun stays within 13 degrees of the horizon (north of about 53.6°N, just beyond Manchester and Dublin), 32 of 33 meters find June midnights brighter, typically 3.7 times. At the observatory in Kielder Forest, Northumberland, 8.6 times. At Grefsenkollen, on a hill above Oslo, anywhere from a few dozen to nearly two hundred times, depending on how the nights are chosen.
RomaniaUnited Kingdomother countries
Where the Sun sinks deeper than 15 degrees, none of 122 finds June midnight more than half a magnitude (1.6 times) brighter than December’s. In between, at 13 to 15 degrees, the 5 meters are split. Between 15 and 18 degrees, the twilight that is left is fainter than the atmosphere’s own glow and the glow of the towns. By the geometry, London has 60 nights without astronomical darkness, yet a meter at Axel in the Netherlands, where the Sun sinks almost exactly as far as over London, finds June midnight darker, not brighter.
The network’s only meter in Romania, at Ciocănari in Vâlcea county, finds midnight as dark in June as in December, slightly darker in fact. So do the 6 meters in Austria at the latitude of Suceava, in Romania’s north, five of them in the Alps. The one exception in the north is a meter in central Nizhny Novgorod, whose December sky is some 190 times brighter than a natural one: there, city light swamps the twilight.
Each thin line is one night of 2026, from 1 January to 31 December. The further down it reaches, the deeper the Sun has gone below the horizon. The dotted lines are the three thresholds: 6, 12 and 18 degrees. A night that does not cross the last one is a night without true darkness.
Added up over the year, the hours of true darkness tell the same story: Bucharest gets 2,948, Edinburgh 2,329. The difference, 619 hours, adds up to nearly 26 whole days of darkness.
How many nights without true darkness each city gets#
The cities on this page, north to south, for 2026. The count moves by a night or two from one year to the next, depending on where the solstice falls.
City
Nights without true darkness
Lowest point on the shortest night
Hours of true darkness a year
Lerwick
122
6.4°
2,170
Oslo
122
6.7°
2,179
Stockholm
118
7.2°
2,200
Inverness
106
9.1°
2,269
Aberdeen
104
9.4°
2,282
Edinburgh
96
10.6°
2,329
Glasgow
96
10.7°
2,332
Newcastle
89
11.6°
2,369
Belfast
86
12.0°
2,385
Leeds
80
12.8°
2,420
Manchester
78
13.1°
2,434
Dublin
76
13.2°
2,441
Berlin
70
14.0°
2,477
Birmingham
68
14.1°
2,480
London
60
15.1°
2,527
Cardiff
59
15.1°
2,529
Paris
18
17.7°
2,690
Vienna
0
18.4°
2,752
Sighetu Marmației
0
18.6°
2,773
Botoșani
0
18.8°
2,785
Baia Mare
0
18.9°
2,791
Suceava
0
18.9°
2,792
Iași
0
19.4°
2,821
Oradea
0
19.5°
2,827
Chișinău
0
19.6°
2,830
Cluj-Napoca
0
19.8°
2,843
Timișoara
0
20.8°
2,892
Brașov
0
20.9°
2,897
Bucharest
0
22.1°
2,948
Craiova
0
22.2°
2,952
Constanța
0
22.4°
2,957
Rome
0
24.7°
3,035
Madrid
0
26.1°
3,078
How it was worked out, and where the evidence stops#
The Sun. Its position comes from Jean Meeus’s formulas (Astronomical Algorithms, chapter 25), the same in the page and in the calculations behind it. Against NASA Jet Propulsion Laboratory’s DE421 ephemeris, the difference is at most 0.006 degrees, and the night counts come out identical for London, Cardiff, Edinburgh, Inverness and Sighetu Marmației. A date’s “night” runs from local noon to the next local noon. The 18-degree threshold applies to the centre of the Sun’s disc, without refraction, as in the U.S. Naval Observatory’s definition.
The sky meters. The data are the monthly files of the STARS4ALL network (TESS-W meters, one reading a minute), published under the Open Database License 1.0. For each night the darkest reading within an hour and a half of midnight was kept, with the Moon at least 5 degrees below the horizon. For each month, the median of the clearer half of the nights (at least six) was taken, ranked by each meter’s own sky-temperature sensor. The counts in each group do not change when all moonless nights are used, or only the dark sites; the ratios of single meters move more. Four June–December pairs were left out: they read darker than any natural sky, the sign of a covered or failing sensor.
How bright the sky stays. The 36 meters that see twilight at midnight (by a looser test than the one in the chapter above) trace one curve together: the sky brightens by about 1.1 magnitudes for each degree the Sun sits higher. With the Sun 10 degrees below the horizon, twilight alone adds 17.8 magnitudes per square arcsecond, consistent with measurements made at Paranal in Chile (18.0 at 10 degrees, and 1.14 per degree between 5 and 10 degrees). That curve lights the sky in the windows above.
What is drawn, not measured. In the windows the stars are real ones (the Yale Bright Star Catalogue), in their true places for the chosen hour and place. How many show is an estimate: the eye’s limit comes from the sky’s brightness by Unihedron’s formula, with 0.25 magnitudes of extinction per air mass, for a place far from any lights. The colour of the glow, its shape across the sky and the hills are drawn. The meters measure in a redder band than the eye sees, so the star count is rounded and approximate. Cloud, the Moon and city light all make the sky brighter than in the windows.
The sky-meter table behind this page, available to download, is derived from STARS4ALL data and is published, like them, under the Open Database License 1.0.
