DENVER - Dr. Steve Lee knows eventually a day will come when life as we know it will come to an end on earth, but thankfully he says that day is not going to be Friday when an asteroid bigger than the space shuttle makes a flyby.

"I can assure you with high probability that we're all going to survive until Saturday," says the Curator of Planetary Sciences at the Denver Museum of Nature and Science. "I think we can say with 100% certainty it will not hit the earth on Friday."

But it doesn't mean the scientific community can't find itself in a scientific tizzy for the time being as asteroid 2012-DA14 makes its way closer and closer to a rendezvous with an area closer to earth than some of its man-made satellites.

"It's about a half football field across," Dr. Lee said.

The asteroid was first spotted a year ago. Friday, it will come closer to the earth than any asteroid of comparable size has done in decades. It won't be visible in Colorado, but will be visible in places like Australia with the help of binoculars or a telescope.

To put it into perspective, it will still be more than 17,000 miles away from earth on Friday. The diameter of the earth is nearly 8,000 miles.

When a similarly sized asteroid made up of rock hit the earth's atmosphere in 1908, it created what's now known as the Tunguska Event over Siberia. While the rock exploded before it could hit the surface of the planet, the resulting blast flattened 750 square miles of forest.

Dr. Lee says scientists worldwide have pinpointed the location of close to 90 percent of the asteroids nearby, but says there always remains the possibility that a few could slip our detection systems.

"It's all a matter of statistics. We know the earth gets hit," he said.

Thankfully, it's pretty rare.