A "supermoon" is seen over Dubai, United Arab Emirates, on Nov. 14, 2016.

Come Sunday night, and a larger-than-usual full moon is likely to greet you with the decade's first supermoon-like experience. While most of the astronomers believe that the full snow moon on February 9 is a supermoon, there are a few who say it is not. Remember, there is no single foolproof definition for the supermoon, and hence the confusion.

Amid all the ambiguity, we asked Mr Pradeep Nayak, a senior astronomer at Khagol Mandal and the author of 'Tarangan: Guide to night sky', to answer to tell us more about this recurring phenomenon. Khagol Mandal is a non-profit collective of astronomy enthusiasts who organise various sky observation programmes, lectures and study tours. Here is what Mr Nayak had to say:

First, can you tell us what a supermoon is?

A 'supermoon' rises at CST in Mumbai on Monday, November 14, 2016,

Supermoon simply means the full moon which appears larger to us than usual when its position in its orbit is nearest to the Earth. According to another definition, it is also the new moon at its closest approach to Earth, but since the new moon is 'Amavasya', we cannot observe the moon that day. There is no official definition of supermoon given by the International Astronomical Union. So, one may find different full moons or new moons as supermoons.

On February 9, there is a full moon day, and it's also a 'supermoon' according to famous Solar and Lunar eclipse scientist, Fred Espenak.

What is the best time and place to witness the supermoon on February 9?

As the sun will set in the west, this supermoon will rise over the eastern horizon. Choose a place from where the eastern horizon is clearly visible. Moon will rise at around 7:10 from Mumbai region. Since our celestial neighbour will be visible throughout the night, you can get a glimpse of brighter and larger than usual supermoon any time during the night. As the moon rises high on the sky, one can witness moon from any suitable place. It might be cold out there. So if you are planning to stay outdoor for a longer time, it is better to protect yourself with warm clothing.

Will the supermoon be visible around the world?

A "super moon" rises near the Lincoln Memorial on March 19, 2011, in Washington, D.C.

As Earth rotates around its axis in 24 hours, entire Earth will be able to observe the full moon on this day. As the day starts from the east, from the International Date Line, the night also starts from there.

Supermoon will be visible to half of the globe at a time. During the nighttime, all seven billion-plus people will be able to watch brightly lit supermoon, provided the sky clear. As the moon approached its 'perigee' with respect to Earth, the apparent size would be larger than usual.

Wait a minute, what do you mean by the 'perigee', and how much do supermoon events vary in size and brightness?

Moon is the most prominent object in the sky. Moon is the closest celestial object to us. Lying at the average distance of 3,84,000 km from Earth, it revolves the Earth about every 27 days.

To understand what is apogee and perigee, we have to remember what we studied during high school. Every planet revolves around the sun in an elliptical orbit, and every ellipse has two foci, i.e., two centres. Sun is on one of the foci. So, when the planet revolves around the sun, planet-sun distances are not constant, but always change. Hence, during the revolution, at one point in its orbit, the planet comes closest to the sun and at another point planet moves farthest from the sun.

Mumbaikars were treated with a bigger and brighter super full moon on Tuesday, Feb 19, 2019.

Same is true for our earth-moon system. When the moon is farthest to Earth in its orbit, at the distance of 4,05,700 km, i.e. 21,700 km further than average, it appears slightly smaller in apparent size. This point on moon's orbit is called as 'apogee'.

When the moon is closest to the Earth in its orbit, it is at the distance of 3,63,100 km from Earth, which is almost 21,000 km closer than the average. At this point, called 'perigee', the moon appears much larger.

Whenever the full moon occurs at or near perigee, it is called 'supermoon'. A supermoon appears around 14 per cent larger and 30 per cent brighter than usual. Of course, the change in size and brightness is not distinctly perceivable to a casual observer. With sophisticated instruments and accurate measurements, one can measure the difference in size as well as brightness.

Is there any impact of this particular phase of the moon on the Earth?

The term supermoon is relatively new. A US astronomer by the name Richard Nolle coined this term about 40 years ago. There are a few predictions of disasters during supermoon day. But, these claims are entirely untrue and have been refuted by scientists all over the world. It is the day as usual for Earth. Apart from a visual treat, the only effect we may observe is slightly higher spring tide. Astronomy enthusiasts now use this event to popularise astronomy.

How many supermoons can we look forward to in 2020?

"Supermoon" appears in the sky over Cairo, Egypt, on Jan. 31, 2018.

In the recent past, there were three consecutive supermoons in October, November and December 2016, which arouse the interest of people all over the world. November 2016 was the largest supermoon in the last 70 years.

The year 2020 is unique in terms of lunar events as we are going to witness four consecutive supermoons: February 9, March 9, April 8 and May 7.

Why the apparent size of the moon visible from the Earth change with time?

As the moon revolves around the Earth in an elliptical orbit, the distance between the Earth and the moon keeps changing. Therefore, the size of the moon also varies according to distance.

There is another factor which changes the size of the moon with timealbeit extremely slowly. The gravitational interaction between the sun, the Earth and the moon, is slowly pulling the moon away from the Earth, at the rate of about 4 cm per year.

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This article was produced in collaboration with Khagol Mandal.

Original post:

Ask An Astronomer: Here's All You Need to Know About Decade's First Supermoon on February 9 - The Weather Channel