Spring Equinox

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Spring equinox is today. The exact time is 23:58 EET (Eastern European Time, that is, my time zone). The length of day is exactly 12 hours 11 minutes in Lahti, Finland at 60.9827° N today. What? Is it not exactly 12 hours? Well, no it isn't. That's because the atmosphere causes the rays of the sun to bend downwards as the density of the atmosphere changes along the trajectory of the rays. The sun appears to be slightly higher above the horizon than it really is, which it why it also appears to spend 11 minutes longer above the horizon than 12 hours.

Incidentally, the length of day in Caracas, Venezuela at 10.4806° N, is 12 hours 6 minutes. Why is it shorter? That's because the difference between the sun's apparent angular distance from the horizon and its actual angular distance from the horizon is at its greatest near the horizon. The sun's trajectory across the sky in equatorial regions is such that it spends less time near the horizon than in polar regions. That is, the sun spends more time close to the zenith than the horizon, which is why mornings and evenings actually take longer the closer to the poles you are.