The Sun shines through portals at ancient monuments on certain days of the year. Given that Earth precesses on its axis every 26,000 years, wouldn't that cause all those alignments to be off?

The short answer is “yes.” But the answer is more complicated than that because two kinds of precession play a role.

The first type of precession to consider is that of the equinox. If you traveled to Chichen Itza on Mexico’s Yucatan Peninsula during the vernal or autumnal equinox, you could still watch the shadow of the 1,100-year-old great snake god Kukulkan slither down the pyramid steps. But that’s not to say it’s exactly the same. In the years since the Maya’s peak, the date of each equinox has actually moved by just more than two weeks.

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