Why is day not equal to night at the equinox?

Why is day not equal to night at the equinox?
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In 2020 the spring equinox occurred on March 20 at 6:49 Moscow time. At this time the Sun was directly above the equator. But if you look at the length of the day, it will not be equal to the night.

The question why comes along with a raised eyebrow! Sunrise for Moscow on 20.03.2020 — 6:31, and sunset — 18:43. Length of the day: 12 hours, 12 minutes, 47 seconds. It turns out that on March 20, the day is almost half an hour longer than the night.

A day when day is equal to night actually occurs a few days before the specified date. In particular, in Moscow, the day was almost equal to the night of March 17 (11 hours 58 minutes 51 seconds).

So why are day and night not equal at the official time of equinox?

First, the Sun is a disk, not a point source of light. Therefore, sunrise is the moment when the upper edge of the solar disk rises above the horizon, and sunset is when the same edge falls below the horizon. It takes a few minutes for the Sun's disk to pass the horizon line (from edge to edge).

The whole sunrise and sunset picture is complemented by the optical effect of refraction of sunlight by the atmosphere. The observer sees the Sun that begins to appear above the horizon, although in fact it is still below the horizon. Similarly, at sunset, the Sun has already disappeared, but the observer can still see it. The combination of these two factors makes the equinox day longer than the night.

That's how deceptive nature can be!

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