Blue hour
Updated October 15, 2026.
Blue hour is the short stretch of morning and evening when the sun is just below the horizon and the light goes cool and blue before it warms up, or after it cools off. In the morning it starts at dawn and ends as the golden hour begins, a little before sunrise. In the evening it starts when the evening golden hour ends, a little after sunset, and it finishes at dusk.
The station page prints both windows as a start and an end, because a single clock time would hide how short they are. On a mid-latitude coast the morning blue hour is often only ten or fifteen minutes. It is longer in summer at high latitudes and it can disappear in the timing of a polar day. If the line is missing, the sun did not pass through that angle.
Who uses it
Photographers named it, and they use it because the sky and the water pick up a color that the middle of the day does not have. On the water it is also a practical mark: it is deep enough into the dawn that you can see, and it is still before the sun is in your eyes. The evening blue hour is the last clearly colored light before dusk settles into nautical twilight.
Blue hour is not a tide. It does not move the water. It is listed with the other light times so a station page matches the sun service the app uses, and so the morning has more marks than sunrise alone.