Do not worry: Tonight’s supermoon, which will appear larger than any moon in the North American night sky since 1992, will not cause any natural disasters, NASA reassured everyone today. They’ve even go so far as to produce a YouTube video to explain the super moon’s effects.
NASA predicts the ‘super perigee moon’ will appear 15 to 30 percent larger than normal. Optimal viewing time, experts say, is just after sunset, when the glowing orb hangs just above the horizon, creating an optical illusion that makes its size appear even greater (an effect known as the “moon illusion”).
The moon, which measures a constant 3,474 kilometers across, isn’t actually changing size. Instead, the moon appears so large because it is at the “perigee” point in its orbit around earth, the closest point in the orbit’s ellipses.
The moon became perigee at roughly 3pm EST today, at which point the moon was a mere 221,565 miles from our planet, about 31,000 miles closer than its furthest distance, know as “apogee.” In addition, the moon became officially a full moon just an hour before hitting becoming perigee — a rare event that creates a stunning visual.
“The full Moon of March 19th occurs less than one hour away from perigee,” says Geoff Chester of the U.S. Naval Observatory in Washington, D.C, “a near-perfect coincidence that happens only every 18 years or so.”
While the close proximity off the moon does increase the its gravitational effects on the oceans to bring about “perigeean tides,” or tides that have a greater range between high and low, the changes are relatively small — about 6 inches more than normal.
So grab your cameras, or binoculars, get outside, and enjoy this magnificent heavenly event — it will be quite some time before you’ll see it again.
Watch NASA’s video about the super perigee moon: