This Halloween will bring a rare treat to the skies, particularly for those who like to howl at the moon.
That's because Saturday will bring a "blue moon," the first to land on Halloween in nearly 20 years.
But don't expect the moon to be blue in color.
A "blue moon," named more for its rarity rather than color, simply means two full moons in one month. The first full moon, called the "harvest moon," was seen on Oct. 1.
"When the phrase 'Once in a blue moon' was coined, it meant something so rare that you would be lucky to see it in your lifetime," according to NASA.
A blue moon actually happens about once every two to three years, but has not been seen on Halloween in the Central and Pacific Time Zones since 2001. According to the Farmers' Almanac it is the first blue moon for all time zones in 76 years, with the last time taking place in 1944.
In Chicago, skies are expected to be mostly to partly cloudy, with cloud increasing as a front passes.