When is the shadow the longest and shortest in a day?

During the day: the shadow is the longest in the morning and the shortest at noon.

Among the four seasons: the shortest shadow day is the summer solstice, and the longest shadow day is the winter solstice.

The shadow is the longest when the sun rises in the morning and evening, because it is closest to the horizon and the minimum angle between the sun and the object is close to the right angle. At noon, the shadow is the shortest, because the sun is at right angles to the irradiated object at the highest position, and the shadow is distributed in a circle at the foot of the object.

When the sun shines directly on the Tropic of Cancer in a year, it coincides with the summer solstice solar terms in northern China. At noon, the sun is directly above the head, that is, the height angle of the sun is 90, which is the maximum in a year and the shadow is the shortest. When the sun shines directly on the Tropic of Capricorn, it coincides with the winter solstice solar terms in northern China. At this time, the sun's altitude angle is 43, which is the minimum value in a year and the shadow is the longest.

Extended data:

Utilization of shadow length

In ancient times, with the help of sundials, shadows were used to judge time. Humans have used sundials for a long time. The ancient Babylonians began to use it 6,000 years ago, and China in the Zhou Dynasty 3,000 years ago. The sundial can display not only the time of day, but also the solar terms and months.

From the vernal equinox to the autumnal equinox, the sun always runs on the north side of the celestial equator, and the shadow of the ray needle is cast above the ray plane; From the autumnal equinox to the vernal equinox, the sun runs on the south side of the celestial equator, and the shadow of the ray needle is cast below the ray plane. So look at the top of the plate after the vernal equinox; Look under the plate after the autumnal equinox.