People of Calcutta will be able to witness a 'supermoon' on Tuesday if the monsoon sky permits, former director of M P Birla Planetarium Debiprosad Duari said.

A supermoon will again be visible by the end of the month on August 30.

The full moon, when it is closest to the Earth, is described as a 'supermoon'.

The last time two supermoons were seen in the same month was in 2018, and the next such phenomenon will be witnessed in 2037, he said.

"It is exciting as this coincides with the time Chandrayaan 3 module will be injected into the lunar transfer trajectory," Duari said.

Chandrayaan 3 is scheduled to make a soft landing on the moon on August 23.

"The moon goes around the Earth once in 27.3 days in an elliptic orbit. As a result, at some point in its orbit, the moon will be farthest from the Earth, with the distant point being called Apogee, while at some other time it will be closest to the Earth, with this point being called Perigee," he said.

"When we have a full moon near Perigee, or closest to the Earth, we get what is called a supermoon," the scientist said.

From the Earth, a supermoon seems 7 per cent bigger and 16 per cent brighter than normal full moon, he said.

The average distance between the Earth and moon is 3,84,000 km. The distance can vary because of the elliptical shape of moon's orbit around the Earth and can range from 3,56,000 km at perigee to 4,04,000 km at apogee.

On Tuesday night, the moon will be at a distance of 3,57,530 km from Earth and will be 100 per cent illuminated by sunlight around 12.01 am, he said.

"In Kolkata, the moon will rise at 6.17 pm. People will get an exciting opportunity to see the big, bright supermoon if the monsoon sky permits," he said.

On August 30, the moon will be even closer, only 3,57,344 km from the Earth.

"As it will be the second full moon in the same month, it will be called a 'blue moon'," he added.

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