Lunar standstills: the 18.6-year cycle behind ancient alignment claims

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Key facts

• A major lunar standstill recurs about every 18.6 years; over one lunation, the Moon reaches its greatest monthly range of northerly and southerly moonrise and moonset.
• At the southern major-standstill extreme, the Moon can rise lower than the winter-solstice Sun in the Northern Hemisphere. The opposite extreme is correspondingly northerly.
• The Moon's roughly monthly declination cycle is often compared with the Sun's annual cycle, but the two cycles are not otherwise equivalent.
• Perigee and apogee recur each lunar orbit. A perigee full or new Moon strengthens tides, while equinoctial conditions can increase flood risk but do not guarantee flooding.
• Callanish's main avenue aligns with the Moon's southern major-standstill rising point; the video interprets this geometry as a deliberate long-term lunar-tracking system.
• The video interprets Chimney Rock's Ancestral Puebloan structures and natural rock portal as a purpose-built lunar-standstill observatory.
• Alexander Thom was a Scottish astronomer who witnessed minor-standstill lunar extremes in the Outer Hebrides.
• The evidence does not establish that Callanish's builders observed the Moon continuously for more than 18 years.

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