A hundred years ago, on June 17, 1908, an event occurred over a remote part of Russia, the likes of which had not been seen before or since.

Something exploded 3-6 miles in the air with far more power than the atomic bomb dropped over Hiroshima in 1945.

A little after 7 a.m. near the Podkamennaya Tunguska River in Siberian Russia, the sky blazed with light, the ground shook like an earthquake, thunder-like explosions were heard and blasts of hot wind blew people off their feet.

Many who witnessed--and survived--the event feared the world was coming to an end.

The result was the virtual devastation of a forest area some 30 miles in diameter where an estimated 80 million trees were felled with their bark and branches stripped off. Surely any animals and humans in the ground-zero area would have been killed.

Fortunately the explosion happened over a largely uninhabited area, but it has been calculated that if it had occurred 5 hours later, it would have exploded over St. Petersburg.

Given the devastation of Hiroshima with a much less powerful bomb, one shudders to think of the effects of this event over a large city.

So what was it? Since it happened years before the creation of nuclear bombs and when human flight was still in its infancy, it was almost certainly of natural rather than human origin.

A number of hypotheses have been put forth, including a few rather wild ones. Some have suggested that Earth was impacted by a black hole or antimatter; others have postulated that an alien spacecraft exploded while trying to land on Earth.

While none of these ideas can be unequivocally disproved, all lack supporting evidence to be taken seriously.

Most scientists think a comet or meteoroid several 10s of meters in diameter exploded shortly before impacting Earth’s surface--a hypothesis backed by good, although not conclusive, evidence.

So what’s the prospect of a repeat? No one can predict for sure, but the late Gene Shoemaker, an impact expert, estimated that these events might be expected once every 300 or so years.

Sky Calendar.

• June 18 Wed.: The full Moon is called Rose Moon, Flower Moon, and Strawberry Moon.

• 20 Fri.: Summer solstice, the longest day of the year, marks the beginning of summer.

• 20 Fri. morning: The Moon is below Jupiter.

• 26 Thu.: The Moon is at 3rd quarter.

• 29 Sun.: Latest sunset at latitude 30 degrees North.

• 30 Mon. morning: The Moon is below the Pleiades star cluster low in the east northeast.

• June 30 and July 1, Mon. and Tue. evenings: Mars passes very near the star Regulus low in the west just after dark.

• July 1 Tue. morning: An hour before sunrise low in the east northeast, look for a thin crescent Moon and the star Aldebaran to its right; between them but nearer the horizon is Mercury, about the same brightness as the star.

• 2 Wed.: The midpoint of the year 2008; and the Moon is new.

• 4 Fri.: The Earth is at aphelion -- its farthest from the Sun in its elliptical orbit -- at 94.3 million miles.

• 4 Fri.: The thin crescent Moon is to the left of the Beehive cluster low in the west an hour after sunset -- binoculars will help spot the cluster.

Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth’s west-to-east rotation.) Evening: As darkness falls Mars and Saturn are setting in the west. Morning: Brilliant Jupiter, rising soon after 10 p.m. is seen in the southwest by morning while Mercury begins its morning stint low in the east.

Stargazer appears every other week. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th, Waco, 76707, (254) 753-6920 or paulderrickwaco@aol.com. See the Stargazer Web site at stargazerpaul.com.