Look to the sky Friday to see a "blue moon." 

But don't expect to see the color blue. A blue moon refers to the rarity of multiple full moons in a month or season. Friday's full moon will be the second in August. The first took place on Aug. 1. 

Two blue moons in a month typically occurs every 2.7 years, according to the Huffington Post. 

The last blue moon was on Dec. 31, 2009.

Best time to see the Blue Moon: The moon will be at its fullest at 8:58 a.m. CST, according to the Farmers' Almanac. 

Get news where you live. Sign up for the Joliet, Channahon-Minooka, Romeoville or Shorewood newsletters.