While Halloween celebrations might be a bit different this year because of the Covid-19 pandemic, you can still count on it to be spooky as a rare blue moon will light up the sky on October 31. No matter where you are in the world, you can certainly get a glimpse of the blue moon as it will be visible everywhere including Hong Kong.

A blue moon occurs when there are two full moons in a single calendar month––so October will have two full moons, one on the first of the month and the other on Halloween. But a blue moon can also be the third or fourth full moon in a single season, according to EarthSky.

Seeing two full moons in a month is rare as there are about 29.5 days between full moons, according to NASA. In fact, a blue moon only occurs every two and a half to three years.

Despite its name, a blue moon isn't actually blue, it looks like your average grey-coloured full moon. But a moon can still appear blue if the atmosphere is filled with dust or smoke particles from a volcanic eruption. For example, the moon appeared in a blue-tinted colour after the volcano, Krakatoa erupted in Indonesia in 1883.

The best thing about blue moons is that you don't need any special equipment to see them––just hope for clear skies because this event only happens once in a blue moon.

See also: 7 Unique And Beautiful Places To Watch The Sunset In Hong Kong