Brace for a once-in-a-blue-moon Halloween, as an expert has confirmed that a rare second full moon of the month can be witnessed this Saturday.
Only one full moon appears in the sky every month — and a second one rarely comes up within the same period. When this astronomical phenomenon happens, the moon is then referred to as ‘blue moon’, explained Ibrahim Al Jarwan, a member of the Arab Union for Astronomy and Space Sciences.
“This month, on October 31, most parts of the world will be seeing this second full moon,” Al Jarwan said. The first full moon of the month was seen on October 2.
The blue moon appears once or twice every three years, he added. Al Jarwan clarified that the moon wouldn’t turn blue, as some might think.
“The different colours the moon mainly come from the impurities in the Earth’s atmosphere, along with the vertical angle the moon makes with the horizon.”
What stargazers may notice on Saturday would be the slight change in the moon’s size, the expert said.
“A ‘micro moon’ occurs when the full moon coincides with the moon at its apogee. This is the farthest distance between the moon and Earth during its monthly cycle — about 406,000km away, and this will happen on Saturday, October 31.”
This astronomical phenomenon always occurs when the moon’s orbit around Earth becomes elliptical. “The point of the orbit closest to Earth is called perigee, while the point farthest from Earth is known as apogee.”
So when it is closest to earth — about 356,000km away — a super moon occurs, he added. The moon moves from apogee to perigee and vice versa every two weeks.
“The apparent change in the moon size from the super moon to the micro moon is no more than 16 per cent, and that is not clearly observed. These terms are used to distinguish between the status of the moon.”