Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2017 August 12

A Day in the Life of a (mostly) Human Sundial
Video Credit & Copyright: Astronomie-AG, Progymnasium Rosenfeld, Till Credner,

Explanation: Have you ever wanted to be a gnomon? Of course, a gnomon is the tall part of a sundial that casts a shadow. The gnomon's shadow moves as the Sun moves across the sky, indicating time by the shadow's position on the dial face. So on July 19th, the Astronomy Group of the Progymnasium Rosenfeld created a human sundial, each participant patiently playing the role of the gnomon for 10 minutes. In this timelapse video of their temporal voyage of discovery, one image was taken every 20 seconds from 8 am until 4 pm Central European Summer Time. Drawn on the ground are the dial hour marks calculated to show the local time for that specific date. Behind, the tower clock offers a time check. Can you find the local time of solar noon? (Hint: At solar noon the Sun is on the meridan.) The persistent group plans a repetition of the human sundial performance next winter to compare the length of the day and the altitude of the Sun.

Tomorrow's picture: miasma of plasma

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