Truly once in a blue moon on Jan 31

A photograph of the occurrence of a total lunar eclipse, shot at 11.45pm on Dec 10, 2011. On Jan 31, Singaporeans will get to see the rare coincidence of the blood moon, blue moon and supermoon phenomena - a total lunar eclipse, the second full moon
A photograph of the occurrence of a total lunar eclipse, shot at 11.45pm on Dec 10, 2011. On Jan 31, Singaporeans will get to see the rare coincidence of the blood moon, blue moon and supermoon phenomena - a total lunar eclipse, the second full moon of the month and the closest full moon respectively.ST FILE PHOTO

Last coincidence of 2 full moons in a month, supermoon and lunar eclipse was in 1866

On Jan 31, a rare astronomical event will occur, a coincidence of three special occurrences of the Moon - a lunar eclipse, a blue moon and a supermoon.

The last time the planets aligned this way was almost 152 years ago, in 1866, a spokesman for the Science Centre Singapore told The Straits Times on Tuesday.

A lunar eclipse occurs when the Moon moves into the Earth's shadow. The Jan 31 event will be the first lunar eclipse of the year.

The Moon during a total lunar eclipse is also called a blood moon due to the red colour it can take on.

Normally, there is only one full moon a calendar month and three full moons in a season, said the spokesman. But Jan 31 will see the second full moon of the month, which is dubbed a blue moon.

It does not appear blue, but is so named for its rarity: It occurs once every two years and eight months.

And the Jan 31 full moon is a supermoon, which occurs when a full moon coincides with the Moon being closest to the Earth.

The last blue moon took place on May 21, 2016, and the last total lunar eclipse visible in Singapore happened on April 4, 2015.

"After this year's total lunar eclipse, it will not be until three years later that we will see another blood moon, on May 26, 2021," said the Science Centre spokesman.

The centre is organising a viewing session from 7.30pm to 10.30pm at the Science Centre Singapore on the day itself.

Over 100 people have signed up for it and 879 have expressed interest on its Facebook page. Admission is free and registration is not required.

Telescopes will be set up for viewing, on a first come, first served basis.

There will be free live planetarium shows about the Moon at the centre's OmniTheatre at 7.30pm and 8pm. And food vendors from Street Food Circus will set up stalls.

There will be bag checks for safety reasons so attendees are advised to travel light for quicker entry. The centre will not be able to accommodate private telescopes.

Previous astronomy-related events have been well received. More than 3,000 turned up for the last eclipse-related event - a partial solar eclipse on March 9, 2016.

If it rains on that day, viewing will stop but will resume if the rain stops by 9.30pm. It will end at 10.30pm, regardless.

The Science Centre has scheduled additional live planetarium shows in case of wet weather.

A version of this article appeared in the print edition of The Straits Times on January 17, 2018, with the headline 'Truly once in a blue moon on Jan 31'. Print Edition | Subscribe