See the sunlight before you go
When does the sun really set behind the mountains?
On 21 December 2027, on the valley floor at Lauterbrunnen, the sun first reaches you at 11:49 and leaves at 13:25, 3 h 18 min before the official sunset at 16:43. That is 1 h 36 min of direct sun on a day with 8 h 34 min of daylight.
Watch the ridge take the sun in Lauterbrunnen →
Official sunset against the last direct sun
Official sunrise and sunset assume a flat horizon. In a valley the ridge decides, and how much it takes changes with the season and with the exact spot. Each row is one public place, computed for 2027 in local time.
| Place | Date | Official sunrise | First direct sun | Last direct sun | Official sunset | Direct sun |
|---|---|---|---|---|---|---|
| Lauterbrunnen valley floor | 20 March | 06:32 | 09:42 | 14:40 | 18:40 | 4 h 58 min of 12 h 8 min |
| Lauterbrunnen valley floor | 21 June | 05:35 | 08:56 | 16:20 | 21:25 | 7 h 25 min of 15 h 50 min |
| Lauterbrunnen valley floor | 21 December | 08:09 | 11:49 | 13:25 | 16:43 | 1 h 36 min of 8 h 34 min |
| Chamonix Place Balmat | 20 March | 06:36 | 09:25 | 17:23 | 18:44 | 7 h 58 min of 12 h 8 min |
| Chamonix Place Balmat | 21 June | 05:41 | 07:38 | 18:50 | 21:26 | 11 h 13 min of 15 h 45 min |
| Chamonix Place Balmat | 21 December | 08:10 | 12:29 | 15:52 | 16:49 | 3 h 1 min of 8 h 39 min |
| Zermatt Kirchplatz | 20 March | 06:32 | 08:52 | 16:32 | 18:41 | 7 h 40 min of 12 h 8 min |
| Zermatt Kirchplatz | 21 June | 05:38 | 07:42 | 18:09 | 21:23 | 10 h 26 min of 15 h 45 min |
| Zermatt Kirchplatz | 21 December | 08:07 | 11:16 | 15:03 | 16:46 | 3 h 47 min of 8 h 38 min |
| Hallstatt Marktplatz | 20 March | 06:09 | 06:56 | 15:03 | 18:17 | 8 h 7 min of 12 h 8 min |
| Hallstatt Marktplatz | 21 June | 05:07 | 07:03 | 17:11 | 21:06 | 10 h 8 min of 15 h 59 min |
| Hallstatt Marktplatz | 21 December | 07:50 | 11:07 | 11:46 | 16:16 | 38 min of 8 h 26 min |
Official times are the standard sunrise and sunset, when the top edge of the sun meets a flat horizon. Terrain times are when the centre of the sun crosses the computed skyline. First and last are outer bounds: if the sun drops behind one peak and returns through a gap, the time between them is not all sunlight, which is why the last column counts only the minutes of direct sun.
Even in June the Lauterbrunnen valley floor gets 7 h 25 min of direct sun out of 15 h 50 min of daylight. The walls are the reason, not the season.
Checked against Rjukan and Viganella
Two towns are famous for months without direct sun, and both installed mirrors to bring it back. They are a fair test, because their sunless periods were published long before Heliora existed, and nothing in Heliora was tuned to them.
Rjukan, Norway, installed a sun mirror in 2013. Heliora computes no direct sun at the town centre from 28 September 2026 to 15 March 2027: 169 days. Visit Rjukan says the town is in shade from mid-October to mid-March, and other accounts give late September to mid-March. The end date matches. So does the late-September start: the sun follows the same low path in late September as in mid-March, so a town that gets its sun back in mid-March loses it in late September.
- Visit Rjukan (official tourist board): “In mid-October, the sun disappears behind the mountains on the south side, and the town is in shade until mid-March.” Source
- Atlas Obscura: “from late September to mid-March” Source
Viganella, Italy, installed a sun mirror in 2006. Heliora computes no direct sun at the village centre from 9 November 2026 to 1 February 2027: 85 days. The published figure is 83 days, from 11 November to 2 February. Heliora's dates are within two days of it at each end.
- Eni / Plenitude (February 2026): “83 days a year, from 11 November to 2 February” Source
Working it out by hand, for free
You can answer this without Heliora. First find how high the skyline stands in the sun's direction: HeyWhatsThat draws a panorama of the peaks around a point, and its path profiler gives the height and distance of the ridge, from which the angle follows. For ridges more than a few kilometres away, allow for the curvature of the Earth. Then take the sun's direction and height through the day from SunCalc, and find the minute the sun drops below the ridge angle in its direction. Repeat for every direction the sun passes through.
Heliora does those steps for every compass degree at once: 360 rays from the pin, out to 30 km in detail and further at coarser resolution, with the sun's crossing found for each direction it passes. The result is drawn as a 3D sky from the pin, and it recomputes when you move the pin or change the date.
Golden hour behind a ridge
Heliora counts sunlight as golden when the centre of the sun is below 6° and clears the terrain. If the ridge is higher than the sun for that whole window, the visible golden hour at that spot is zero, even though the sky may still glow. Find a better day ranks the longest continuous golden-hour windows for the pin. It does not forecast clouds or photographic quality.
Explore a terrain example
How these numbers are computed, and where they can be wrong: Method and accuracy.