As the next full moon nears, a rare new moon marks the end of 2024 — the black moon. The black moon is a rare celestial phenomena that happens roughly every 29 months or longer. The last one occurred in August of 2022 and the next won't come again until May of 2026.

That's because a black moon is the term for the second new moon to fall in a single calendar month, and new moons appear invisible to the naked eye from Earth. While new moons happen throughout the year, two new moons only fall in a single calendar month about once every 29 months, according to the Old Farmer's Almanac.

On Monday, observers of the skies will once again have the opportunity to experience a rare "black moon." There was already a black moon on December 1, which makes this celestial phenomenon extremely rare.