Blue Moon will rise Saturday night (May 21), and you can watch it with expert commentary online during a live Slooh webcast from the Institute of Astrophysics of the Canary Islands.

The free program is a collaboration between the online Slooh Community Observatory and "The Old Farmer's Almanac," and will run from 8 to 8:30 p.m. EDT (0000 to 0030 GMT on Sunday, May 22). You can follow the Slooh webcast at

You can also watch the Blue Moon webcast on, courtesy of Slooh.

Thought to be called "blue" after an old english term meaning "betrayer," a Blue Moon is an extra full moon that occurs due to a quirk of the calendar. [<a href="">See the full Blue Moon Infographic here</a>.]
Thought to be called "blue" after an old english term meaning "betrayer," a Blue Moon is an extra full moon that occurs due to a quirk of the calendar. [See the full Blue Moon Infographic here.]
Credit: Karl Tate,

Saturday's Blue Moon won't actually appear blue. Instead, the term Blue Moon refers to the third full moon in a season that features four full moons, rather than of the typical three. Blue Moons occur about once every 2.7 years. The second full moon in a calendar month is commonly considered a Blue Moon, but that rule doesn't always hold up. For instance, this is the first full moon of May, but it is still a Blue Moon. [Blue Moon Photos of 2015: Amazing Full Moon Views]

Saturday's full moon is known as the Full Flower Moon, heralding the arrival of summer flowers. It is also known as the Full Corn Planting Moon and the Milk Moon. Slooh's live broadcast will discuss the origin of the moon's name, how to calculate a Blue Moon and how the moon's location was once key evidence in a murder trial, Slooh representatives said in a statement. Viewers also can go to to watch the broadcast, snap and share photos during the event, personally control Slooh's telescopes, and interact with the webcast hosts and audience members.

"This webcast marks the newest installment in a partnership between Slooh and'The Old Farmer's Almanac,' with a mission to connect each other's audiences to the miraculous ebb and flow of nature as caused by celestial bodies; moments of wonder we all take for granted but are no less delighted to be exposed to again and again," they said in the statement.

Editor's note: While May's Blue Moon won't actually be blue in color, it will still be a spectacular sight. So if you snap an amazing photo of the full moon Saturday and would like to share it with and our news partners for a possible story or image gallery, send images and comments to managing editor Tariq Malik at

Email Sarah Lewin at or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+. Original article on