It was an unusual coincidence of events. The Moon reached its very closest point on that morning. A few hours after that was the instant called full moon.

 It is in fact, not so unusual. The elliptical orbit of the moon brings it closer; takes it farther exactly twice in a month. Just as an eagle looks small when it is high up, the moon should appear larger and smaller as this distance varies. These two instants are called perigee and apogee. If one were to take the photograph of the moon throughout the month with the same camera settings and compare them, the change in size becomes apparent. This can happen at any phase of the moon. If the perigee and apogee coincide with the quarters, the difference shows up very easily.

 If one does not have a camera it is not possible to find out when the moon is apogee or perigee. However, if the perigee coincides with a full moon or new moon, the fishermen can sense that the tides are unusually high. The small difference in the distance can cause a noticeable difference.

On the other hand, what happens if the moon is farthest on a full moon day? Quite naturally it will look the smallest. This is slated for the month of May. On 20th at 07:41am, the event of full moon occurs. Same evening at 07:56pm, the moon is farthest. Thus, the full moon should appear smaller and less bright than normal. This is an opportunity to understand the meaning of apogee and perigee.

Since the moon is at apogee and perigee approximately 15 days apart, we have an interesting scenario on next new moon, namely 3rd June. At 18:42 the moon is at perige; within about six hours at 12:53 am of 4th, it is new moon. Therefore, if at all we could “see” the moon, it would have been the smallest. The tides on the ocean would be the highest.

On May 20, the distance to the moon is 408,000 km, while it is 358,200 km on June 3. Notice the deviation from the mean distance is barely 7%.

So it is really true, that the Moon will be smallest on May 20, as the numbers put it. But will it be ever possible to judge it just by looking at it? Or can we judge that the full moon this month is dimmer than what it usually is? No!
 Try clicking the moon with your camera; note down the settings. Repeat the exercise every full moon. You will get a meaningful result after seven months — in December!

In any case, these are issues only for the astronomical record books. (The angular radius of the moon would be 14’ 42.39” on May 20 and 16’ 43.5” on June 3. Remember 1degree = 60’) This month's full Moon won't look dramatically smaller and dimmer than normal. Most people won't notice a thing.

Only those fishermen who plunge into the sea regularly, would notice unusually high tides on June 3 and not so high tides (as compared any full moon day) on May 20. (They may not be reading this.)

Jawaharlal Nehru Planetarium