How to use the midnight sun latitude calculator
Choose a hemisphere, enter the latitude of the site, and the page reports whether the midnight sun and the polar night can happen there, how much latitude is left to the polar circle, and the solar declination needed for the sun to stay up all day. When picking a destination or planning an observing trip, the latitude alone settles whether it is possible at all. Enter the start and end dates from a local almanac as well and the page counts the span in days and finds its middle date.
How the numbers are produced
The polar circle at 66.5 degrees is the geometric complement of the 23.5-degree axial tilt, and the declination needed is 90 degrees minus the latitude entered. Occurrence is decided by whether the latitude reaches 66.5 degrees, with the boundary itself counted as inside. Day counts use coordinated universal time components, so as of October 2026 the same values appear in any time zone.
Limits and what is not covered
The page publishes no table of midnight-sun or polar-night periods by region. It does not model the way refraction pushes the real boundary a little below the polar circle, horizons blocked by mountains or buildings, or the stretches when twilight keeps the night from going fully dark.
Frequently asked questions
The axis of the earth tilts about 23.5 degrees against the plane of its orbit, so the declination of the sun reaches 23.5 degrees at most. From the complement of that angle, 66.5 degrees, there are days when the sun stays above the horizon all day. The polar circle is that geometric boundary.
For the sun never to set at the latitude you entered, its declination has to reach at least 90 degrees minus that latitude. When the figure comes out larger than 23.5 degrees, no day of the year clears it, so the midnight sun cannot occur there.
The real length of the midnight sun and the polar night shifts from place to place with atmospheric refraction and the local horizon, so the page publishes no regional table. Enter the start and end dates from a local almanac and it counts the days and the middle date from those two values only.