Updated: It Really is a Blue Moon for Oregon, Portland, Coast

Published 07/28/2015 at 5:04 PM PDT - Updated 07/29/2015 at 1:04 AM PDT
By Oregon Coast Beach Connection staff

(Oregon Coast) – This time around, what's in the skies above western Oregon – including the coast, Portland, Eugene, etc – really is happening once in a blue moon.

The moon was already full on July 2, and this month we get a double dose as it happens again on July 31. This is typically called a blue moon: when you have two full moons in a calendar month. Given the coming heatwave – with even the beaches maybe hitting sizable highs – it's likely to be good weather for soaking in the midnight sun.

Jim Todd, planetarium manager and astronomy expert for Portland's OMSI, said the first full moon happened on July 1 at exactly 7:20 p.m., Oregon time. The next happens this Friday at 3:43 a.m.

“A blue Moon occurs every 3 to 4 years, when the date for one full moon falls on or near the beginning of a calendar month so that the following full moon comes before the end of the same month,” Todd said.

Todd said the meaning of the term “blue moon” is a varied one. Some of its use goes back nearly 400 years, but during that time its meaning has shifted around a lot. More recently, the term was cited in The Maine Farmers' Almanac, 1937.

“The almanac states that when there were two full moons in a calendar month, calendars would put the first in red, the second in blue,” Todd said.

For astronomers, the term means the second full moon in a month, and that tends to be the more common usage.

In meteorology, however, the weatherman may use it differently. The correct definition in that case has to do with the moon actually turning blue, and the scientific explanation why.

“The Moon can also have a bluish color on very cold winter nights when ice crystals in the air form a ring around the moon,” Todd said. “The scattering of moonlight by smoke particulate causes a 'blue moon.' The red end of the spectrum is scattered more than the blue end of the spectrum, which causes light seen from the Moon to look more blue: hence, a blue moon.”

This is not an uncommon sight on the Oregon coast. Ocean mist can increase the chances of seeing a slightly bluer lunar face above the beaches.

Todd said despite the differences in meaning, in general terms, the rarity of seeing a moon that looks blue and/or the rarity of two full moons appearing in one month prompted the well-known saying "once in a blue moon," which means something that happens very rarely.

The last blue moon occurred in August 2012, and the next will be in January 2018. More Oregon coast science here.

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