How Elevation Affects Sunset and Dusk Times
Stand higher and you see farther around the curve of the Earth, so the sun takes longer to disappear. That much is intuitive. The size of the effect is not, and the number most often quoted for it is wrong by a factor of five.
Why Height Delays Sunset
Sunset at Olympic National Park in Washington
At sea level your horizon is a level line. Climb, and it drops below level, because you can now see over the bulge of the planet. Navigators call that drop the dip of the horizon, and they have been correcting sextant readings for it for centuries.
The sun has to travel that extra angular distance before it clears your lower horizon. Since the sun descends at a fixed rate, extra angle means extra time.
The dip grows with the square root of your height, not in proportion to it. Doubling your elevation does not double the delay; it multiplies it by about 1.4. That is why any rule shaped like “one minute per X meters” is broken by construction, and it is why the first 100 meters buy you more than the next 900.
The Actual Numbers
Dip in arcminutes is close to 1.76 times the square root of your height in meters. Converting that to time depends on your latitude, because the sun sets vertically at the equator and at an increasingly shallow slant as you move toward the poles.
Sunrise from Cadillac Mountain, Acadia National Park, Maine. The summit is 466 meters up at 44.3 degrees north, with open ocean to the east, which is the ideal case for this effect: the sun clears the horizon about 3.5 minutes earlier here than for someone standing on the shore below.
For an observer around 40 degrees latitude, with a clear view to a sea-level horizon:
| Your elevation | Sunset delayed by |
|---|---|
| 100 m (330 ft) | about 1.5 min |
| 500 m (1,640 ft) | about 3.5 min |
| 1,000 m (3,280 ft) | about 5 min |
| 2,000 m (6,560 ft) | about 7 min |
| 4,000 m (13,120 ft) | about 10 min |
Near the equator, subtract roughly a quarter. At 60 degrees latitude, add roughly half again, because the sun is crawling toward the horizon at a shallow angle and each extra degree of dip costs more time. From the summit of Denali at 63 degrees north, the delay runs to about 20 minutes.
The Rule of Thumb That Will Not Die
Plenty of sources, including this article until it was corrected, repeat that sunset is delayed by about one minute for every 1,500 meters of elevation. The claim traces back to press coverage of a Dubai fasting ruling and does not survive contact with that same story’s own numbers.
In 2011 the Dubai Islamic Affairs Department ruled that residents of the Burj Khalifa should break their Ramadan fast on a schedule that varies by floor. Residents between the 80th and 150th floors wait two extra minutes. Above the 150th, three minutes.
The 80th floor sits around 300 meters up. Run that through the dip formula at Dubai’s latitude and you get 2.2 minutes. The 150th floor is around 585 meters, which works out to 3.1 minutes. Both land on the ruling’s own figures.
Now apply the popular rule to the same building. One minute per 1,500 meters would predict a delay of about 12 seconds at the 80th floor. The ruling says two minutes. The rule of thumb and the observation it supposedly came from disagree by a factor of ten, and the physics sides with the observation.
Dusk Gets Shorter, Not Longer
This is the part that trips up most write-ups on the subject, and it is worth being precise about.
Twilight phases are defined by the sun’s true angle below the horizontal, not by what you can see. Civil twilight ends when the sun’s center reaches 6 degrees down, nautical at 12, astronomical at 18. Those thresholds are geometric and do not change with your elevation.
Sunset is different. Sunset depends on your visible horizon, which does move when you climb.
So elevation pushes sunset later while leaving the end of twilight where it was. The gap between them closes. On a 2,000 meter peak at mid-latitude, sunset arrives about 7 minutes later than at the base, but full dark arrives at the same moment it always did, meaning your window from sunset to darkness is 7 minutes shorter.
You watch the sun set later and lose the light faster. Anyone who has been caught descending a mountain at dusk has felt the second half of that without knowing the reason.
When None of This Applies
The whole calculation assumes your horizon is far below you and unobstructed. Three situations break it:
A high plateau gives you nothing. If the ground to your west sits at the same elevation you do, your horizon is at eye level and there is no dip to collect. Denver is a mile up and its sunset is essentially a sea-level sunset, because the plains west of it are not.
Mountains to your west take the sun early. Terrain nearly always beats elevation in practice. A ridge a few kilometers away that rises 5 degrees above your horizontal will cut about 25 minutes off your day, swamping any elevation bonus.
Haze near the horizon can hide the last of the sun entirely. On thick days the disk often fades out a degree or two above the true horizon, and the sun you were waiting for simply never arrives.
Does Elevation Change Refraction?
It does, in the opposite direction from what you might guess.
Atmospheric refraction bends sunlight and lifts the sun’s apparent position by about 34 arcminutes at the horizon for a sea-level observer. That bending happens in the dense air near the surface. Climb above part of that air and there is less of it left to do the bending, so refraction at altitude is somewhat weaker.
The effect is small and pushes against the dip effect rather than adding to it. Dip wins comfortably at any elevation you are likely to stand at, which is why the net result is still a later sunset. Any source claiming thin mountain air makes refraction stronger has it backwards.
Other Things That Move Sunset
Latitude does most of the work. It sets how steeply the sun meets the horizon, which controls both the length of twilight and how much any elevation correction is worth. The full treatment is in how sunrise is calculated.
Season matters through the same mechanism, since the sun’s declination changes the angle of its path. Winter sunsets tend to look different for reasons of air clarity rather than geometry.
Atmospheric conditions change what you see rather than when. Cloud cover and air quality decide whether there is anything worth watching.
To find real times for a specific place, use the sunrise and sunset calculator, then apply the table above if you are heading somewhere high with a clear western view. If you want to know how much usable light you have afterward, how long it takes to get dark has the twilight numbers by latitude.