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Astronomers may be unable to observe some of the fainter stars and galaxies as the Sun passes this mark.Īstronomical dawn marks the beginning of astronomical twilight, which lasts until nautical dawn.Īpril and May is the best time to view earthshine However, at this point, the twilight is so faint that it is generally indistinguishable from night, especially in areas with light pollution. The Earth's upper atmosphere begins to scatter and reflect the sunlight, illuminating the lower atmosphere.

When the Sun passes the elevation angle of -18 degrees as it ascends towards the horizon before sunrise, a very small portion of its rays begin to permeate the firmament. Precise dawn and sunrise times for your city Astronomical Dawn

Civil dawn – the geometric center of the Sun's disk is 6 degrees below the horizon.

Nautical dawn – the geometric center of the Sun's disk is 12 degrees below the horizon.

Astronomical dawn – the geometric center of the Sun's disk is 18 degrees below the horizon.

As with dusk, astronomers differentiate between three different stages of dawn, each marking the beginning of one of the three phases of morning twilight:

Science specifies dawn as a particular moment defined by the solar elevation angle, which is the position of the Sun in relation to the horizon. ©/kavalenkava volha Scientific Definition

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