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<\/a> Looking eastward at the rising Moon just past Full on the night of May 31st. Credit: Stellarium.<\/p>\nBlue Moon Blues<\/p>\n
Now, this is the second Full Moon of May 2026, making it a \u2018Blue Moon<\/a>\u2019 in the modern sense. But don\u2019t expect the Moon to actually appear blue in color. This term actually stems from an error published in Sky &; Telescope in 1946, referring to the superfluous second Moon of a calendar month. That definition actually comes down from the now defunct Maine Farmer\u2019s Almanac, which used the even more Byzantine distinction of the \u2018third Full Moon, in an astronomical season with four.\u2019 Legend has it, they denoted the extra Moon with blue ink.<\/p>\n Moreover, second Full Moons in a month aren\u2019t all that rare, and occur roughly once every 2-3 years.<\/p>\n On very rare occasions, the Moon can physically appear Blue, as happened on the night of September 23rd, 1950 over eastern North America, when the Moon seen to take on a bluish cast. This was due to muskeg fires in far to the west in Alberta, Canada, suspending ash and debris high in the atmosphere. This acted as a natural airborne filter. Ironically, the Moon was at waxing gibbous and two days from Full at the time. <\/p>\n Next, the May 31st Full Moon is the Minimoon for 2026<\/a>, in the sense that it\u2019s the visually smallest of the year. This you can actually see, if you compare it to the perigee (Super) Moon on the night of August 30th\/31st later this summer. The Moon\u2019s path is slightly elliptical, taking it from a near perigee of around 363,300 kilometers, to an apogee of 405,500 kilometers once per orbit. <\/p>\n This means that the Moon can appear anywhere from 29.3\u2019 to 34.1\u2019 across. When a solar eclipse occurs near lunar apogee, the Moon appears too small to cover the Sun, and an annular eclipse occurs. <\/p>\n But how rare is a Minimoon<\/a>, with a Full Moon less than 24 hours from apogee\u2026 and a Blue Moon<\/a>? Well, the last time this occurred was on October 30th, 2020 (-20 hours apart), and the next won\u2019t happen until (mark your calendars) July 31st, 2080 (18 hours apart). To give you some sense how rare that is, the final Blue Minimoon for the 21st century is on January 31st 2094 (less than an hour apart!)<\/p>\n You can play with Fourmilab\u2019s Lunar Perigee and Apogee calculator<\/a> to see how these line up by year. Incidentally, Google\u2019s AI gets these 21st century dates wrong, telling me I still have a job in astro-forecasting anomalous events, at least for now.<\/p>\n How about a Blue Minimoon, with a lunar eclipse? Scanning though the calendar, there are none in the 21st century, though there was a Super (Perigee) Blood Moon total lunar eclipse<\/a> on Jan 31st, 2018. They\u2019re pretty rare, indeed.<\/p>\n It\u2019s also worth noting that said Full Blue Minimoon occults the bright star Antares for eastern Australia, New Zealand, the South Pacific and the southern tip of South America on May 31st, just an hour after passing Full. The rest of us see a close pairing of the two worldwide. <\/p>\n Clouded out this weekend? You can actually watch the Blue Minimoon Live online<\/a>, courtesy of astronomer Gianluca Masi and the Virtual Telescope Project: <\/p>\n<\/a> Blue and Black Moons for the current decade. Credit: Dave Dickinson.<\/p>\n<\/a> The Super vs. Minimoon. Credit: Ken Lord.<\/p>\n<\/a> The Antares lunar occultation footprint. Credit: Occult 4.2.<\/p>\n