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Bioluminescent BaysPuerto Rico

The almanac

The Moon Calendar

The moon phase matters more than the season for seeing bioluminescence. The best nights fall within three days of a new moon, when the sky is darkest. A full moon can wash out the glow almost completely, in any bay, any month.

Best window: new moon, plus or minus three nights
New moon, darkest sky
Full moon, glow at its weakest

July

Anno MMXXVI · 2026

New · Jul 14
Full · Jul 29

New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.

August

Anno MMXXVI · 2026

New · Aug 12
Full · Aug 28

New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.

September

Anno MMXXVI · 2026

New · Sep 11
Full · Sep 26

New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.

October

Anno MMXXVI · 2026

New · Oct 10
Full · Oct 26

New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.

November

Anno MMXXVI · 2026

New · Nov 9
Full · Nov 24

New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.

December

Anno MMXXVI · 2026

New · Dec 9
Full · Dec 24

New moon and the three nights on either side, when the glow is strongest. Struck dates mark the full moon, when it is weakest.

Bioluminescent dinoflagellates glow when disturbed, and that glow is genuinely faint. Any light pollution, moonlight included, drowns it out. A new moon gives the darkest sky, which is why the window above is built around it, not around the season or the weather forecast.