Super Moon: Have you ever wondered about or even tried to look at the size of the Full moons afft different times throughout the year and noted a difference in size? You may ask why? The Moon goes around the earth in an elliptical orbit so it is not at the same distance from us all the time (as it’s not a circle), as a result it appears to grow and shrink by a small amount, as seen in the skies (though it does not grow or shrink physically!!).
And the size difference is more apparent on the day of the full moon when we see the whole disk illuminated. Now just imagine seeing a bigger full moon – it means that moon is at perigee (point nearest to earth) or near perigee at that time. As its a bigger moon then there has to be a name to it as we humans are very much inclined towards giving names to each and every thing!! They call it SuperMoon!! And this word was coined recently in late 70’s (if we talk about time scales in astronomy).
And its interesting to know that SuperMoon is a word which was not coined by astronomers but by an astrologer, Richard Nolle, who is credited with coining the term ‘Supermoon’. He arbitrarily defined this as
. . . a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth.
But for astronomers a Supermoon is the full/new moon happening at the exact time of perigee so there is no ambiguity about the definition. Now our new definition becomes – . . . a new or full moon which occurs with the moon at its closest approach (perigee) to Earth. The technical name is the perigee-syzygy of the Earth-Moon-Sun system. We astronomers do not use the term “SuperMoon” but among the masses its a catchy word!
As we have Supermoon, there has to also be ‘Micromoon’, which happens at Full moon at the time of Apogee. And if you happen to click both the moons with same setup, you would find a drastic change in apparent diameter which is around 14% and thats quite large!!
Now lets see how many Full Moons fit into this definition. We have not taken New Moon in this category as it can’t be seen at all!!! But a Supermoon at new moon at the time of an eclipse also plays a different game, that I leave to you all to ponder.
In the present century we have the following SuperMoons, which fit in the definition of Full Moon and Perigee moon happening exactly at same time (Perigee happening at F +/- 0 h):
Now you would wander as why the perigee distance is also changing? That’s another point to discuss some other time!
There are quite a lot of more so called supermoons if we relax our stringent rules to allow for few hours +/- difference between Full Moon and Perigee Moon. You would find that 14th November Full Moon (Supermoon) has not been listed in my list at all. Let’s see why is has not been done by SPACE whereas the rest of the world and the social media is abuzz with the news that this is the biggest full moon during the past 70 years! Biggest full moon means that the full moon has to happen exactly at perigee but whether its happening or not, and on top of that where on earth we are witnessing it as it plays a major part. In case we all are more interested in numbers (aren’t we?), let’s find out.
On 14th November, the Full moon is happening at 13:54 UT (19:24 IST) and perigee is happening 2 hours before full moon so at full moon the distance to the moon would be 356536 kms so there is the catch. If Usain Bolt even finishes 100 mts 0.001 seconds ahead of the other he would win. The same case here in this ‘supermoon’, that if numbers don’t speak, we can’t help it! But in any case numbers or no numbers, a full moon almost close to perigee point i.e. close to earth is truly worth watching.
You can see that there is one supermoon coming on 14th November 2016. So what’s the big deal about it? Well on that day the Full Moon will be approximately 14% bigger than the Full Moon on Apogee and will be 30% more brighter than it. If you plan to click the image on that day then make sure that you click with same setup another image on March 5th next year, when we have the Full Moon happening near to Apogee and then you can actually visually see and calculate the difference we have talked about. The image above is an example of such a comparison which we did in 2011. And another interesting thing about this is when you see the above image and the pair you will take, you will see the phenomenon which we call as libration of the Moon, well that’s once again another story to tell!!!!
But do enjoy the illuminated Moonlight dinner on that night with your near and dear ones!!
Written by CB Devgun
President, SPACE Foundation