The Great Daylight Fireball of 1972.

This famous photo depicts an earth-grazing meteor, a comparatively rare event.

The Great Daylight Fireball of 1972.

The photo above, a rather famous one, was taken 51 years ago today, August 10, 1972, at Jackson Lake, Wyoming. If you don't notice it immediately it will become clear after a few seconds of looking at it: the fiery object crossing the sky in a glowing trail. The mountains in the background are the Tetons. The fireball became visible at about 2:30 that afternoon over Utah, and streaked across the sky in a northerly direction, exiting the Earth's atmosphere over the Canadian province of Alberta. The "Great Daylight Fireball," also known as the "Grand Teton Meteor," was a particularly spectacular example of a comparatively rare event, an Earth-grazing meteor that bounced off our atmosphere, rather like a stone skipping across the surface of a pond, instead of impacting somewhere on the ground.

Astronomers have estimated that the meteor involved in this event was about the size of a small truck and probably passed within about 35 miles of the Earth's surface. It may have been part of a group of asteroids called the Apollo Asteroids, which orbit the inner solar system and occasionally pass near the Earth. The spectacular "Chelyabinsk fireball" of 2013, which was the subject of a rash of startling YouTube and cell camera videos when it passed over Russia, was one of the Apollos. Apparently we're not sure this particular meteor, the one that skipped off the atmosphere in August 1972, is still out there. It might come back, or perhaps not. The close pass with Earth apparently reduced its size and mass, kind of like an ice cube melting as it slides across a warm range top.

I love this photo and it's one of my favorite astronomical-historical pictures. The meteor takes a few moments to notice, but the guy in the red shirt transfixed by it is a nice touch and leads your eye to it. Imagine you were out boating on this lake on this ordinary summer day, looked up and saw this. There is also video footage of the August 1972 fireball, but because of the low-res grainy picture available at that time, it's not as impressive, I think, as the still photo.

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