The second Full Moon of the month – Blue Moon (not necessarily blue in color) – shined in the sky on October 31. The simplified definiton of “Blue Moon” says that it is the second Full Moon in one month and the expression “once in a blue moon” means that something happens very rare, almost never.
That rare Full Moon earned the color blue in its name probably after the 1883 Krakatoa volcano eruption in Indonesia, when the dust haze caused the visual effect of green sunrises and sunsets and a blue Moon.
The coincidence of Full Moon and Halloween is quite rare – it occurs 3-4 times per century (the next ones will be in 2039, 2058, 2077 and in 2096).
During Full Blue Moon and later in November Mars still shines bright in the sky.