Astronomical twilight is the darkest of the twilight phases. How is it defined and when does it start and end? What are astronomical dawn and astronomical dusk?

Twilight occurs according to the solar elevation angle θ s, which is the position of the geometric center of the Sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (nearest the horizon), nautical twilight, and astronomical twilight (farthest from the horizon). [2]

Astronomical twilight occurs when the Sun is between 12 degrees and 18 degrees below the horizon. Astronomical dawn is the time when the center of the Sun is at 18 degrees below the horizon. Astronomical dusk is the instant when the center …

Astronomical twilight is the darkest twilight phase. It starts when the center of the sun is 12 degrees below the horizon until 18 degrees below the horizon. After 18 degrees, it is considered ‘night’ or ‘dark’.

2022年7月27日 · Astronomical twilight is a period of time in which the sun is below the horizon but some of its light is still being scattered between air molecules and bounced back to an...

2022年9月9日 · Astronomical twilight. When the darkness is almost complete, and the horizon isn’t discernible, it means that the astronomical twilight is here. The Milky Way starts to appear, and the faintest stars and planets can be observed with the naked eye unless the Moon illuminates the sky.

2024年8月16日 · The darkest twilight stage is astronomical twilight. The definition of astronomical twilight is the period of time when the center of the sun is 12 degrees below the horizon to 18 degrees...

Astronomical twilight occurs when the Sun’s center is between 12 and 18 degrees below the horizon. After this point, the faintest stars emerge. The conclusion of this stage of twilight heralds the arrival of full darkness. See the Almanac’s sunrise/set calculator to get all three twilight times!

2023年7月5日 · Most of us think of twilight as a single period of transition from bright day to deep night, but there are actually three twilights: civil, nautical, and astronomical. Each is defined by how...

2007年8月23日 · It's astronomical twilight, the time when the Sun is 12° to 18° below the horizon. In cities and bright suburbs, or at full Moon, astronomical twilight is a non-issue; the sky is as dark as it ever gets by the end of nautical twilight.