Make plans now to step outside just before sunset on Saturday, April 12.
If you do, and if the sky is clear, you’ll be able to watch the beautiful full moon rising over the eastern horizon.
Now you may say that it looks close enough to touch, but much of what you’ll see that night isn’t real.
It’s an optical trick known as the “moon illusion” that our brains play on us to make the moon appear larger than it really is.
Many of us learned the moon’s distance while we were in grade school, and some of us still remember it: about 240,000 miles from Earth.
The key word in the previous sentence, however, is “about,” because the moon doesn’t remain at a constant distance.
That’s because the moon orbits our planet not along a circular path but rather along an elliptical path — sort of a squashed circle.
And this means that, over its monthly journey, the moon swings closer and farther by about 25,000 miles. So that distance many of us remember is close to its average distance of 238,855 miles.
Fortunately, the moon’s distance doesn’t vary much more because that would mean that its gravitational pull would also be more variable.
Without a relatively constant gravitational attraction from our celestial neighbor, our ocean tides might never have made it possible for life to emerge from the seas eons ago, and we certainly would not be around to ponder this issue!
As large as the April 12 full moon may appear, it will lie near apogee — its farthest point from the Earth.
At a distance of some 252,264 miles, this full moon will be the farthest (and the smallest) of the entire year, despite what your eyes and brain may tell you!
Nearly seven months later, on Nov. 5, the full moon will occur while near its “perigee” — its closest point to Earth.
At this time the moon will lie only 221,726 miles from us and will appear as the largest full moon of 2025. At these times you will hear it referred to as a “super moon,” even though there’s really nothing “super” about it.
It’s not difficult to measure how much the moon’s size appears to change because of its varying distance.
If you have a camera with a telephoto lens that can capture a closeup shot of the moon, take a picture on April 12 and another on Nov. 5, using the same gear and settings.
When you put those two images side by side, you’ll see just how little the moon’s apparent size has changed as a result of its varying distance from the Earth.
Of course, casual stargazers don’t need to know the moon’s exact distance, but astronomers who study the moon, as well as scientists and engineers who send spacecraft there, certainly do.
So to get the most precise measurements, they bounce powerful laser beams off reflectors that were placed on the lunar surface decades ago by Apollo astronauts and can measure the moon’s distance to an accuracy of less than 1 inch!
All we need to do is go outdoors on April 12 and enjoy the view!
