astronomical twilight

Astronomical twilight is when the sun is between 12 and 18 below the horizon.

I sit and watch from civil twilight until astronomical twilight.

In some places, especially those with sky glow, astronomical twilight may be almost indistinguishable from night.

Az & El both report dark after astronomical twilight.

Thus, this bee is an example of an insect that can perceive polarization patterns throughout astronomical twilight.

The duration of astronomical twilight depends on the length of the path taken by the sun below the horizon.

At this latitude at midnight the summer sun is only 16.56 below the horizon, which means that astronomical twilight continues the whole night.

See also civil twilight and astronomical twilight.

The astronomical polar night is a period of continuous night where no astronomical twilight occurs.

Astronomical Twilight ends about 2100 hrs.

It happens when there is no nautical twilight and only astronomical twilight occurs at the solar culmination.

Astronomical twilight happens when the sun is between twelve and eighteen degrees below the horizon and astronomical night when it is even lower.

There are three established and widely accepted subcategories of twilight: civil twilight (brightest), nautical twilight, and astronomical twilight (darkest).

There is no astronomical twilight at the poles near the winter solstice (for about 74 days at the North Pole and about 80 days at the South Pole).

At the end of Nautical twilight the horizon is no longer visible, and at the end of Astronomical twilight the indirect illumination from the Sun is less bright than starlight.

From the end of astronomical twilight in the evening to the beginning of astronomical twilight in the morning, the sky (away from urban light pollution) is dark enough for all astronomical observations.

Twilight patterns are produced during the time period between the beginning of astronomical twilight (when the sun is 18 below the horizon) and sunrise, or sunset and the end of astronomical twilight.