What is the blue hour?

The blue hour is the period of twilight just before sunrise and just after sunset when the sun sits between 6 degrees and 0 degrees below the horizon (civil twilight). Sunlight scatters heavily in the atmosphere, bathing the sky in a cool, deep blue that photographers, cinematographers and architects prize for its soft, even, directionless quality. It typically lasts 20 to 40 minutes depending on your latitude and the time of year.

How is the blue hour calculated?

The calculator uses the NOAA solar-position algorithm (based on Jean Meeus "Astronomical Algorithms"). It computes the solar declination and the equation of time from the Julian Day Number, then solves the hour-angle equation cos(HA) = (cos(z) - sin(lat)*sin(dec)) / (cos(lat)*cos(dec)) for each zenith angle z. The blue hour corresponds to solar elevations from 0 degrees (standard horizon, zenith 90.833 degrees with atmospheric refraction) to -6 degrees (civil twilight, zenith 96 degrees). The golden hour corresponds to elevations from -4 degrees to +6 degrees.

What is the difference between civil, nautical and astronomical twilight?

Civil twilight runs from sunset (0 degrees elevation) to -6 degrees below the horizon — the sky is still bright enough for outdoor activity without artificial light. Nautical twilight spans -6 degrees to -12 degrees — the horizon is just visible at sea, stars are bright, but the sky has a distinct blue-grey cast. Astronomical twilight covers -12 degrees to -18 degrees — only then is the sky truly dark enough for faint-object astronomy.

When is the best time for blue hour photography?

Evening blue hour (just after sunset) is generally preferable for planning because you can arrive before sunset, shoot golden hour, then stay for the blue hour. The sky cools from warm oranges to deep indigo in roughly 20-40 minutes. Morning blue hour ends at sunrise, so you must be in position before dawn. Use the calculator to get the exact window for your chosen day and location.

How long does the blue hour actually last?

Typically 20 to 40 minutes at mid-latitudes, but it varies considerably. Near the equator the sun drops steeply below the horizon, so twilight can be as short as 15 minutes. At high latitudes (above 60 degrees North or South) the sun travels at a shallow angle and the blue hour can extend to an hour or more — and around the summer solstice it may blend directly into the opposite twilight without a true night.

Does this calculator work for polar regions?

Yes. If the sun never rises (polar night) or never sets (midnight sun) on your chosen date, the calculator detects this and shows the appropriate message instead of producing times. The detection uses the same solar declination and latitude comparison that drives the mathematical singularity in the hour-angle formula.

Is GPS permission required?

No. Typing latitude and longitude manually works without any location permission. The "Use my location" button requests browser geolocation to fill the coordinates for you — you can dismiss the permission prompt and type in coordinates instead. All computation runs locally; no coordinates are sent to a server.

Blue Hour Calculator

The blue hour is among the most coveted windows in photography, filmmaking and architectural visualisation — a narrow band of soft, cool light that exists only while the sun sits between the horizon and six degrees below it. Outside that window everything changes: below -6 degrees the sky darkens toward nautical twilight; above 0 degrees daylight crowds out the delicate hue. This calculator pins that window to the minute for any place on Earth and any date you choose.

How it works

The tool implements the NOAA Solar Calculator algorithm derived from Jean Meeus’s Astronomical Algorithms. Starting from your date, it computes a Julian Day Number and derives the sun’s geometric mean longitude, mean anomaly and equation of centre to obtain the true ecliptic longitude. It then corrects for the nutation and aberration of the apparent longitude, solves for the solar declination, and builds the Equation of Time — the offset between mean solar time and true solar time that can reach plus or minus 16 minutes.

From those values it derives solar noon in UTC:

Solar noon (UT) = (720 - 4 * longitude - EqT) / 60

For each light phase it then solves the hour-angle equation:

cos(HA) = (cos(z) - sin(lat) * sin(dec)) / (cos(lat) * cos(dec))

where z is the target zenith angle, lat is observer latitude and dec is solar declination. The rise and set times are solar noon minus or plus HA / 15 (converting degrees to hours). The calculator solves this for six zenith values in sequence:

Phase	Elevation	Zenith
Sunrise / sunset	0° (with refraction)	90.833°
Golden hour boundary	+6°	84°
Golden hour / blue hour overlap	-4°	94°
Civil twilight (blue hour)	-6°	96°
Nautical twilight	-12°	102°
Astronomical twilight	-18°	108°

If cos(HA) falls outside the range -1 to +1, the sun never reaches that elevation on that date — the calculator reports this as polar conditions (midnight sun or polar night) rather than producing a meaningless time.

Worked example

London (51.5074° N, -0.1278° E) on 21 June 2026:

Astronomical dawn: 02:49
Nautical dawn: 03:30
Morning blue hour: 04:07 – 04:45
Sunrise: 04:45
Morning golden hour: 04:45 – 05:37
Solar noon: 13:01
Evening golden hour: 20:25 – 21:17
Sunset: 21:17
Evening blue hour: 21:17 – 21:55
Nautical dusk: 22:43

Blue hour duration each way: approximately 38 minutes — substantially longer than a winter evening (which drops to roughly 24 minutes near the solstice in December at the same latitude). The shallow solar angle at high latitudes on summer evenings is the reason for this extended twilight.

Formula note

The atmospheric refraction correction of 0.833 degrees embedded in the standard zenith (90.833 degrees) accounts for the fact that the sun appears on the horizon when its geometric position is already 0.5 degrees below it (refraction lifts the image) plus approximately 0.267 degrees for the upper limb of the solar disc. All times are accurate to within approximately one minute for latitudes between -65 degrees and +65 degrees. At extreme latitudes, close to polar day or polar night transitions, accuracy degrades as the solar path becomes very shallow and small atmospheric-pressure variations alter refraction unpredictably.