Week of Oct. 13-19, 2019
Several times a year, we hear big news about the supermoon — when the full moon appears largest in our sky.
Why, however, do we rarely hear about the full moon appearing at its smallest? Why doesn't this make the headlines? Why don't we get inflated news reports about this?
Well, get ready. In the often overblown style we hear on TV or read on the internet, let me offer the following: If you step outdoors on the evening of Sunday, Oct. 13, and look skyward, you will see a spectacular sight that few have ever seen: the minimoon!
Of course, this is total baloney, just as all the "supermoon" hype is. Neither is all that rare, and neither is all that noticeable.
It is true that the moon changes its apparent size in our sky. That's because it doesn't remain at a constant distance from us, as it would if it orbited Earth in a circular path. Instead, it travels along an elliptical path and therefore alters its distance — and the size it appears — throughout its monthly orbit.
Fortunately, this change is not huge. Without the moon's relatively constant gravitational pull, the tides would never have made it possible for life to emerge from the seas eons ago.
On Oct. 13, the full moon will lie near apogee, its farthest point from Earth, and will appear as the smallest full moon of 2019. The exact time of apogee will have occurred two days earlier, but when the full moon rises on Oct. 13, it will lie about 249,170 miles from us.
So, will you actually notice that Sunday's full moon appears smaller than average — a minimoon? Perhaps, but only if you've convinced yourself in advance that it should appear smaller. Otherwise, I suspect it won't be obvious to the average stargazer.
Part of the reason is that our memory of such things is not reliable; in fact, only experienced moon-watchers might be able to detect this mere 4% reduction from its average size.
Now, while this is a relatively minor difference, we can see it easily by comparing two full moon photographs — one taken near apogee and another near perigee (its closest point to Earth). You can easily create such a photo comparison for yourself.
Use a camera with a long telephoto lens (300-400 millimeters will do nicely), and set your camera to manual mode and ISO 200; then try 1/250 second at f-stop 8 to start, but try some other exposures to make sure that something turns out well.
Capture one image on Oct. 13, and, using the same settings, shoot another on April 7 — the night of the closest full moon of 2020. By comparing these two images side by side, you'll discover that this month's full moon appears slightly smaller than that of next April, but only by about 12% — probably not enough for beginner sky-watchers to notice easily with the unaided eye, but more than enough for your photos to show a significant difference.
Whether or not you can notice a difference, it should still be fun to get out at dusk on Sunday to check it out!
Visit Dennis Mammana at facebook.com/DennisMammana. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.
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