What is zenith sun?

In astronomy, the zenith is roughly understood as the point in the sky directly above the observer's head. More precisely, the following definitions are equivalent:

1. It is the point with an elevation of +90 degrees.
2. It is the vertex of the horizon coordinate system.
3. It is the intersection point between the celestial sphere and a line drawn from the center of the Earth through the observer's position on the Earth's surface.

The point opposite the zenith on the celestial sphere is called the celestial equator .

The celestial meridian passes through the zenith, the celestial horizon, and the two celestial poles (North-South).

In the celestial coordinate system, the zenith angle is the angle between the vertical and the position of a celestial body and is the subtrahend to the elevation angle, that is, the angle with respect to the horizontal (horizon).

If the zenith angle of the Sun is 0°, the Sun is 90° overhead and we say the Sun is at its zenith.

The shadow of a tree on the ground is shortest when the Sun is directly overhead (zenith). This phenomenon can only occur at solar noon on certain days in the tropics, when the latitude of the location is equal to the declination of the Sun.

On Earth, observers located in the region between the Tropic of Cancer and the Tropic of Capricorn (including the equator) will observe the Sun reaching its zenith twice a year.

Observers located exactly on the two tropics can only observe the Sun at the zenith once a year (on the winter solstice for the Tropic of Cancer and the summer solstice for the Tropic of Cancer).

Observers located at latitudes above the Tropic of Cancer or below the Tropic of Capricorn will never observe the Sun passing through the zenith.

The place where the Sun is at its highest point in the sky is called the solar ecliptic.

The sun is at its zenith at the Tropic of Cancer on June 22 (summer solstice) and at the Tropic of Capricorn on December 22 (winter solstice). At the equator, the sun is at its zenith twice a year, on March 20 (spring equinox) and September 23 (autumnal equinox).