Shadow ratio

The ratio between the height of an object or surface and the length of its shadow on a plane.

Shooting star

Popular term for a meteor. See meteor.

Solar day

Time period that takes place between one solar noon and the next. Although defined as 24 hours, in solar time most days are slightly longer than 24 hours.Time and Date

Solar noon

An event that occurs when the sun crosses the meridian of the location and reaches the highest point in the sky. In most places, it doesn’t happen at 12 noon. Time and Date

Solar wind

Constant flow of high-energy particles (mostly electrons and protons) that come out of the sun at high speed and temperature. The auroras are caused by the interaction of the solar wind and our atmosphere. Time and Date


Event that occurs twice a year (June and December solstice) when the sun is exactly above the Tropic of Cancer or the Tropic of Capricorn. The winter solstice is the shortest day of the year and traces the lowest arc in the sky, while the summer solstice is the longest, tracing the highest arc.

Tropic of Cancer,  Tropic of Capricorn,  Wikipedia

Southern Hemisphere

Half of the Earth that lies south of the equator.  Wikipedia.

Southern Lights

See auroras.

Star Trail

Line, arc, or circle that draws a star in the night sky in a photo using a long exposure on a fixed-mount camera, it is caused by the Earth’s rotation on its axis in which it appears that it is the stars that slowly rotate in the sky. Wikipedia.

Synodic Month

Time required by the moon to pass through all its phases, measured from the new moon to the next. Also known as lunar month or lunation. Time and Date

Summer solstice

Event that marks the beginning of summer, with the longest day of the year and the shortest night. In the northern hemisphere, it occurs in June, while in the southern hemisphere it occurs in December. Time and Date


Star at the center of our Solar System. Wikipedia.


The moment when the sun appears on the horizon. Time and Date /  Wikipedia.


The moment when the sun disappears completely behind the horizon. Time and Date /  Wikipedia.


A full moon that occurs when the moon’s orbit is at the near point of the Earth (perigee) producing a moon of greater size and brightness than normal. Time and Date / Wikipedia.

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