For the first time in months, nautical twilight spread across parts of the Interior. This means that many Alaskans, including those in Fairbanks, finally got to experience some darkness.

Nautical twilight is defined as the time the geometric center of the sun is 12 degrees below the horizon. This is the time when it's dark enough that lights are required in order to see — something Fairbanks hasn't experienced since May 16.

The sun officially reached 12 degrees below the horizon in Fairbanks at 1:30 a.m. on July 28, then started illuminating the sky just 55 minutes later at 2:25 a.m.

That brief moment was the first time in 73 days that nautical twilight spread over parts of the Interior. 

Nautical twilight gets its name from its sea-fairing roots. It's the time when most stars can be seen with the naked eye and enough light illuminates the horizon to make out distant landmasses at sea. In the past, this was the best time for navigation of open waters using the stars.

Twilight lasts much longer in Alaska than it does closer to the equator because the sun sets at a greater angle. Near the equator, the sun moves almost perpendicular to the horizon. That means it spends less time in each of the twilight zones as it sets.

In Alaska, we are much closer to the poles. The sun rises and sets at an angle and spends more time in each twilight zone, making twilight last longer.

Fairbanks will experience astronomical twilight for the first time on August 18, then the first official night since April on Sept. 5. Utqiavik will experience its first sunset since May 11 on Friday, Aug. 2.

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