The Supermoon is Just a Moon: What’s the Big Deal about it?
There was a time when lunar eclipses were for the geeks. People would look at a lunar eclipse and owe it to ‘Rahu’ and ‘Ketu’ or whatever dumb story they heard about it. I used to be the one to explain to them the science behind the event and they would either think of me as ‘mad’ or ‘genius’ as per their preferences.
Today, every kid seems to know about it. But the whole hullabaloo about the ‘SuperMoon’ seems so dumb.
We all know now that the Moon orbits the Earth on an elliptical path. Hence, the distance between the Moon and Earth varies from 362,600 km to 4,05,400 km. When the moon is closer to us, it seems larger and brighter. If it occurs during the full moon phase, it is called the ‘SuperMoon’.
That’s the whole story. There is nothing new here. The Moon has been doing it for billions of years and humans may have first noticed about its growing and waning size at the time of Greek philosophers!
It’s the Angular Size at which we see the Moon that varies and not the Size of the Moon!
Let’s have a demonstration of the Moon vs SuperMoon. Let’s take a tennis ball which has a diameter of about 6.6 cm which is placed at the distance r from a human being. Now, change its angular size with respect to the human being by moving it closer and then farther away from him (just as Moon does).
Here are the equations to demonstrate it:
We find that the closest value at which a tennis ball stands to represent the SuperMoon = 6.89 m while the farthest value at which it stands to represent the reverse (shall we call it as PunyMoon?) = 7.70 m.
The size of the tennis ball does not really change. It’s just about how it looks to us.
Here are some things to try the next time you see a SuperMoon phenomenon:
• Notice that your thumb at arm’s length has the same angular size as the moon from your head. Now, check how much closer you need to bring your thumb to your eye to cover up the SuperMoon.
• Calculate the %change in the apparent diameter, apparent area, and brightness of PunyMoon vs Moon vs SuperMoon (To measure the brightness, you can assume that the moon is a point light source and hence, 1/r2 expression can be used.)