Why does a supermoon look so big?

SupermoonA very rare astronomical event is taking place where the moon will look significantly larger and brighter than usual.

A supermoon is a full moon that occurs when the moon is closest to the earth’s surface on its elliptical orbit. While this is a physically remarkable in itself, the psychological effect of how we perceive it is much greater.

Claus-Christian Carbon (CCC), a professor of psycholCCC-L_Ausschnitt2ogy and methodology at The University of Bamberg, Germany, is an expert within this field and has recently conducted an experiment examining the psychology behind our perceptions of the moon’s size. Ahead of the big event , we caught up with CCC to find out what his experiment means for the supermoon eclipse and what we should be looking out for.

  1. Hi CCC, can you tell us a little more of what we can expect to see?

First of all, you will be in for a short night’s sleep if you would like to watch it. But I strongly recommend foregoing sleep because, if you have a clear sight, you will have an extraordinary perceptual experience. In the early hours of Tuesday morning we will have the nearest, and so biggest, moon possible.  We will also see a total moon eclipse with a full moon and as the moon will be eclipsed for more than an hour when it is positioned near to the horizon, is it then that we will perceive a huge supermoon.

We call the phenomenon of the moon being perceived much large near the horizon the so-called “moon illusion”: actually, the moon shows the same distance from the Earth independently from being at the horizon or the firmament—still, we perceive the moon extremely enlarged in the first case, and this will exactly be its position when we face the supermoon full eclipse. Importantly, people imagine a total moon eclipse incorrectly: you should not think of a full coverage of the moon but scattered light that will turn the cold bright light of the moon into a mystical looking red lighted moon—a wonderful perceptual experience for which the loss of sleep will be quite worthwhile.

  1. Your research in the planetarium examines the moon illusion. What does this mean in terms of this supermoon?

When we investigated the moon illusion, so the dependence of perceived size in relation to the moon’s elevation in the planetarium, we were quite astonished that first of all there was no moon illusion detectable at all and second, the moon always looked extremely small. This means that even a “super moon”, which relates to a moon which is enlarged in size of about 5%, is not the key factor for the perceived size of the moon but other factors, beyond mere statistics, affect the visual angle of the moon.

  1. What does your research tell us about how we perceive differences?

What we mainly found out was that psychological factors are much more important in everyday life than physical factors when we address a perceptual phenomenon.

  1. This is obviously a very exciting event, and one that some of us may only see a few times in our lives – what should we be looking out for and how can we maximise the way that we see and experience this eclipse?

You need a good observation point, undoubtedly. But even then you need a clear sky—so if you face problems in getting these necessary pre-conditions, try to optimize your standpoint, even if you experience suboptimal settings during the start of the event, because you’ll have more than an hour to experience the total eclipse. Furthermore, trust your eyes not your camera—although the redness of the moon might be of some interest for photographers to shoot, the perceptual size of the moon is mainly based on a psychological phenomenon so camera shots will disappoint you later on, especially if you take panorama shots.


“The Moon as a Tiny Bright Disc: Insights From Observations in the Planetarium” by Claus-Christian Carbon, published in the journal Perception, will be free to access for a limited time and can be read here.  




This entry was posted in Earth & Environment, Psychology, SAGE Connection and tagged . Bookmark the permalink.

Leave a Reply