Case 1
- Which date?
- 20532
- Latitude
- 34°
- Longitude
- -118.2°
- UTC offset on that date
- -7h
- Which edge of the blue hour?
- Evening, begins (sun at −4°)
19.33h
Open with these valuesBlue Hour Calculator
19.61h
Result: 19.61 hThe blue hour runs while the sun sits between 4° and 6° below the horizon. In Los Angeles on 20 March 2026 the evening one starts at 19.33 h — 19:20 local time — and ends at 19.49 h, ten minutes later. The date field opens on today, so check it before you plan.
The numbers at a glance
Held fixed: Which date? 2026-08-30, Latitude 34.0000 °, Longitude -118.2000 °, Which edge of the blue hour? Evening, begins (sun at −4°).
| UTC offset on that date (h) | Result (h) |
|---|---|
| -12.00 | 14.61 |
| -10.00 | 16.61 |
| -8.00 | 18.61 |
| -7.00Your value | 19.61 |
| -6.00 | 20.61 |
| -4.00 | 22.61 |
| -2.00 | 0.61 |
Worked examples
Case 2
- Which date?
- 20532
- Latitude
- 52.52°
- Longitude
- 13.405°
- UTC offset on that date
- 1h
- Which edge of the blue hour?
- Morning, begins (sun at −6°)
5.59h
Open with these valuesCase 3
- Which date?
- 20808
- Latitude
- -33.8688°
- Longitude
- 151.2093°
- UTC offset on that date
- 11h
- Which edge of the blue hour?
- Evening, begins (sun at −4°)
20.39h
Open with these valuesHow it's calculated
local time at which the sun's geometric elevation reaches −4° or −6°
- StepTurn the date into a Julian day and read the sun's declination and the equation of time from it.
- StepWork out solar noon for your longitude and UTC offset.
- StepSearch the half-day before or after noon for the moment the geometric elevation hits −4° or −6°.
- ResultRead the answer as decimal hours: 19.33 h is 19:20.
What this number means
The blue hour is the stretch of twilight when the sun has already set but the sky still carries light. Its edges are angles, not clock times: the sun between 4° and 6° below the horizon. The outer one is standard — the US Naval Observatory puts the start of morning and the end of evening civil twilight exactly there, measured geometrically, with no correction for the way air bends light. The inner edge at 4° is the photographers' convention and marks the handover to and from the golden hour. What you get is cool, almost shadowless light with a deep blue cast, because the ozone layer absorbs the long red wavelengths along the very long path the light now takes through the air. That is Chappuis absorption, a different mechanism from the Rayleigh scattering that makes a midday sky blue. The window is short and it is not an hour. At the latitude of Los Angeles it runs about ten minutes at the equinox; near the equator the sun drops almost vertically and it is shorter still; at high latitudes in summer it crosses those two degrees at a shallow angle and the window can last an hour or more. Above roughly 60° in midsummer the sun may never reach 6° down at all, and the calculator then returns the moment it sits lowest. All of this assumes a flat horizon at sea level. Hills, buildings and haze move the light; the numbers know nothing of them.
Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon.
Where the 6° comes from
It is the standard definition of civil twilight, not a photography rule. The US Naval Observatory measures it geometrically, so no refraction correction is applied.
High latitudes have no blue hour
Above roughly 60° the midsummer sun may never sink 6° below the horizon. The calculator then hands back the time of its lowest point instead.
The tripod matters more than the time
Light falls off steeply across those two degrees. A shutter speed that works at the start of the window is well short by the end of it.
Commonly misread
The blue hour lasts an hour.
It rarely does. Ten to thirty minutes is typical, and the length depends on your latitude and the season.
The blue hour starts at sunset.
It starts once the sun is already 4° below the horizon. At the latitude of Los Angeles that is about fifteen minutes after sunset.
A grey sky means the calculator was wrong.
The times are astronomical and assume clear air. Cloud and haze block the blue cast without moving the sun.
Reference table
| Phase | Sun elevation | Local time | Decimal hours |
|---|---|---|---|
| Morning blue hour begins | −6° | 06:31 | 6.52 |
| Morning blue hour ends | −4° | 06:41 | 6.68 |
| Evening blue hour begins | −4° | 19:20 | 19.33 |
| Evening blue hour ends | −6° | 19:30 | 19.49 |
Questions
What exactly is the blue hour?
It is the twilight window, twice a day, when the sun sits between 4° and 6° below the horizon. The sky takes on a deep blue cast and the light is cool, even and almost shadowless. Landscape and architecture photographers plan around it.
How does the blue hour differ from the golden hour?
The golden hour has the sun just above and just below the horizon, giving warm, strongly directional light and long shadows. The blue hour follows straight after in the evening and precedes it in the morning, with the sun further down and the light cool and flat.
How long does the blue hour last?
Rarely a full hour. Ten to thirty minutes covers most places and seasons; near the equator it is shorter, at high latitudes in summer far longer.
Why is my sky grey instead of blue?
The deep blue comes from Chappuis absorption in the ozone layer, and cloud or heavy haze blocks it. The calculation knows nothing about weather, so check the forecast alongside the times.
Why is the answer a decimal hour?
Decimal hours write the minutes as a fraction of an hour, which is the form solar formulas carry time in. A result of 19.33 h means 19:20, because 0.33 of an hour is 20 minutes.
Does this match the golden hour page exactly?
Almost. That page reads the sun's apparent elevation, which includes atmospheric refraction, because its source defines the edges that way; this one reads the geometric elevation, as the twilight definition does. At the shared 4° edge the two differ by roughly half a minute.
Sources and last check
Information, not professional advice.