BRILLIANT ORB: The full moon above Victoria Memorial Hall on Thursday evening. Picture by Pabitra Das

The moon was at its biggest and brightest on Thursday night — 14 per cent bigger and 30 per cent brighter than the average full moon.

In case you missed out on moon-gazing, keep your eye on the sky, as it will remain as big and bright on Friday, too. “Sometimes, a full moon is actually larger and this time’s full moon is a sure winner,” said Debiprosad Duari, the director of research and academic at MP Birla Planetarium.

The moon’s orbit around the earth is an ellipse with an eccentricity of 0.05. When the moon is at its closest point in its orbit, called the perigee, it is roughly 50,000 km closer to the earth than the farthest point in its orbit, called the apogee. “If this phenomenon of the moon coming close to the earth coincides with a full moon day, the moon is bigger and brighter than the average full moon,” explained Duari.

The full moon phase will be completed around 10.22am on Friday and it will be closest to earth around 4.22pm on Friday. The moon-earth distance will be 356,754 km. Such a phenomenon was last sighted on December 22, 1999, and the next time a full moon will draw so close to the earth will be on December 12, 2008.

“The full moon becoming brighter and bigger will not have any adverse effect. One can gaze at the full moon with the naked eye, but those watching the moon with a binocular or a small telescope must use a filter, since staring at such a bright moon may cause irritation to the eyes,” cautioned Duari.

“But, on some occasions, it has been noticed that the high tide in the ocean is a little higher days after such a full moon event,” he added.

The mean distance between the earth and the moon is considered to be 384,401 km, while at its furthest point in the orbit, it can be 406,500km away. Scientists calculating the orbit of the moon said the closest perigee in the past two centuries was 3,56,375 km on January 4, 1912.

“This time, the pictures sent by Chang-e (Moon Goddess), the Chinese lunar orbiter, will show three-dimensional pictures of the moon’s surface, throwing a lot of light on this unique positioning,” said R.K. Manchanda from the department of astronomy and astrophysics at Tata Institute of Fundamental Research.

The increased size and luminousity is a result of the coming together of a host of crucial factors. These include the clarity of the night sky, level of pollution and the place on the earth from where the moon is being viewed.

“One of the most crucial factors, of course, is the liberation percentage of the moon. This means, the visibility of more than 50 per cent of the moon surface. Generally, a particular half of the moon is seem on full moon nights. Sometimes more than half is visible. This is called liberation. The October 25-26 full moons are larger than others,” explained Manchanda.

Director of Maharashtra-based Akashganga Centre for Astronomy Bharat Adur said usually, the full moon is southward positioned during this time of the year (October to December). “So, on Thursday/Friday, while observing from the equatorial regions, the moon will appear much brighter,” he added.

On how to determine that the moon will look bigger, experts said: “Stretch your hand and keep your index finger towards the moon, which usually covers its apparent diameter. But on Thursday and Friday, the moon will appear slightly larger than the index finger — this is one way to prove the big full moon.”