How big will the Moon be on its perigee (supermoon)?

Dear Children of God,

You have heard probably the announcement that there will be "supermoon" today. It claims that the moon will be "extra big" compared to the previous full moons in the last 18 years you have seen it. That is if you took the time to watch the full moons for the past 18 years. By the way, when was the last time you had a moon observation?


The more basic question is, "How big would it be?"

Before I answer the question quantitatively let me tell you that before you can make any comparison you should have a reference point. This would mean that you have an idea at least how large the moon is during full moons. But my darling you cannot exactly tell the difference by mere observation that the moon would appear 10 to 15% larger. In other words the change in size is imperceptible and momentarily to ordinary observation. To those who requested for telescope viewing, remember that telescope will just make appear heavenly objects (roy, it is not what you think of, ok?) seem near but it won't necessarily magnify it. Jay Albert, of the Astronomical Society of the Palm Beaches, said the best way to view it will be with the naked eye, not a telescope. The lunar surface will be too bright to easily discern mountains and craters.

You see it would be hard for us to tell that Sharon slimmed down if we have not seen how fat she was before? We cannot also tell if someone became taller not until we have seen him months before. So it is important that we have a basis or point of reference.


Will the moon be brighter during supermoon?

I can understand if an ordinary citizen would ask me this but not from a scholar. Haven't you thought of comparing it to a flash light with small and big aperture (aperture: the diameter of the flash light opening end). In other words with the increase in size is the increase in brightness by 30% than lesser full moons (when the moon is at its farthest from Earth). Of course this depends on weather condition during observation.

Supermoon VS. Perigee

Supermoon is for astrology while perigee is for astronomy. Astrology is for those who still cling to their nomadic instinct of thinking that stars' position has bearing to their daily existence. Astronomy is the scientific study of the cosmos and that is what we do in the Physics laboratory.

But why are they using the term supermoon than perigee? Well, some would like to get in touch with their nomadic instinct. Perigee on the other hand would sound peri gee! my hair smells terrific. Peri means near while gee refers to with respect to. This can be likened to perihelium which means that any object which is at its nearest with respect to helium or sun.


Why is there a perigee?

Perigee is the result of moon's elliptical orbit around the earth. Being elliptical there are times that its position is near or far with respect to the psoition of the earth. This holds true in the case of earth and Sun system.


There are times when Moon appears bigger. This happens when Moon is near horizon. How does this happen?

This is but an optical illusion. The explanation lies on how our brains calculate the distance and size of objects in the sky in the case of the Moon.

Take the following iluustration below for instance:

If you simply glance at the picture above the round image below appears bigger than the round image above. Now I want you to get a measuring device and measure the diameter of the image and you will be surprised to find out that they are the same.

It is not magic. The illusion is due to the nearby objects from which we based the size of the image. It is best explained by the illustration below.

Try to compare the two orange circles above. They look different (in size) right? But wait they are just the same in size. Our brain however would interpret the image as if the orange circle in left is smaller than the orange circle in right. The culprit? Yes, the blue circles surrounding it. In sky, when Moon is near the horizon it appears "bigger" than usual because of the buildings, mountains or vegetation we associate its size. That is why when Moon is at the zenith (zenith is the location of the object above your head when you look up), it appears small to us.

Scientific lesson of the story:
- If you are dark-skinned refrain from wearing clothes which will enhance your skin tone.
- If you are short then dont stand beside someone who is taller than you do.
- If you are fat then refrain from being with thinner than you do.
- If your set of teeth is yellowish then wear "dark-toned" lipstick.

So to take advantage of the supermoon I mean the unusual perigee of the Moon as it rises from the horizon.


Clear skies,

siraris