Close encounters of the three kinds

Last month brought some excitement in the way of space rocks falling to Earth, passing by Earth, or, as is periodically the case, supposedly threatening to snuff out all life on Earth.

In the early morning of Feb. 15, local time-late night on Valentine's Day for us-a meteor tore through the atmosphere above the Russian city of Chelyabinsk, injuring more than 1,000 people and blowing out windows across the region in a massive shock wave that sent smaller meteorites falling to Earth.

NASA scientists eventually estimated the meteor to be 55 feet around, 10,000 tons and clocked in around 40,000 miles an hour when it exploded.

The meteor momentarily shone brighter than the sun during the encounter, which occurred just hours before the 150-foot-wide asteroid 2012 DA14 passed Earth in an extremely close flyby approximately 17,000 miles away.

These events were coincidental and unrelated. We knew about the asteroid ahead of time. (The meteor was a different story-but thanks to ever-vigilant Russian drivers dealing with wayward pedestrian scam artists on their streets, the surprise spectacle was caught on countless dashboard cameras.) And in a couple of weeks, Comet PanSTARRS is expected to become visible to the naked eye.

Often when events like this occur, the news is reported with a bit of a twist. An approaching object is weighed and measured, then estimates are made as to the destruction said object would cause if it struck Earth.

Admittedly, the Chelyabinsk meteor added fuel to the fire, but almost every time, the object has a zero percent chance of intersecting with our planet. The media has a fun time spicing up the story anyway with doomsday prophecies that aren't going to happen.

Sky & Telescope magazine recently reported that PanSTARRS is already preparing to disappoint us, and is now only estimated to reach fainter magnitude +2 or +3 instead of -1 as originally hoped. That means it will still be visible to the naked eye, just not as bright.

Here's the issue: PanSTARRS is a new comet expelled from the outer Oort Cloud encountering the sun's heat for the first time. Comets making their first pass by the sun tend to blaze brightly early on, only to fade after a thin, initial coating of ice on the nucleus, or body of the comet, evaporates, S & T says.

The following discussion recently arose here in the newsroom: Just what is the difference between a meteor, comet and asteroid?

A meteor is a free-floating small rock or particle of debris - anywhere in size from a dust particle to 30 feet or so in diameter - that burns up as it passes through Earth's atmosphere. What we call shooting stars actually are meteors.

A comet is a relatively small solar system body that orbits the sun. They can have a periodic orbit every few years or just pass by once. As they make their closest approach to the sun, they display a visible coma (fuzzy outline) and sometimes a tail.

Asteroids are similar to comets in definition but lack a visible coma.

Bonus definition: If a meteor, comet or asteroid withstands destruction from its atmospheric entry and hits the ground, then it is called a meteorite.

Comet PanSTARRS was discovered about two years ago, likely after traveling for millions of years from the Oort Cloud, a reservoir of millions of small, rocky bodies orbiting the sun about a light-year away. PanSTARRS, which is named for the instruments that discovered it, will make its closest approach to Earth on March 5.

November 2013 will bring a similar comet, Comet ISON.

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SKY CALENDAR

March 17: Conjunction of the moon and Jupiter. The moon will be about one and a half degrees away from Jupiter in the evening sky. Look for both objects in the west after sunset.

March 20: March equinox. The sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. This is the first day of spring in the Northern Hemisphere and the first day of fall in the Southern Hemisphere.

March 27: Full moon

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