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This got us thinking: What happens when smaller (and bigger) objects fly into our atmosphere? We used Purdue University's "Impact: Earth!" simulator to find our answers. Our own Bob Al-Greene illustrated the results, as seen in the gallery above.

Some highlights: Rocks the size of basketballs enter our planet about once a month; most burn apart in the atmosphere before they reach the surface. Objects as long as standard school buses (roughly 12 meters around) only sneak into the Earth every 20 years or so - but, as seen in Chelyabinsk, the damage can be much greater.

All results assume the object is traveling at a 45-degree angle, with a density level of 3000 kg/m^3 and a velocity of 11 km/s. Everything is assumed to be seen from 100 kilometers away from the direct impact zone.

Click "Show As List" on the bottom-left of the gallery to view larger images. And check out our Google Hangout with asteroid experts to learn more about what's being done to fend off space rocks, from basketball-sized to London-sized.

It's a warm, sunny day in April, and all the trees are in bloom. But how did they know it was warm and sunny? And on a warm, sunny day in February, what keeps them from blooming? Scott Aker, a horticulturalist at the U.S. National Arboretum, tells Robinson Meyer how the process works and what to look for.

How the Eye Functions - Diagrams of structure of the human eye. How light waves are refracted by lens of eye & focused on the retina. The lens, its position & changes in curvature. Monocular & binocular vision, retina and function.

"Astronomers are worried. It's not some new unexplained mystery of the universe or the upcoming launch of a space telescope that is unnerving them, though. The problems they currently face are much more down-to-Earth - and the future of space exploration hangs in the balance. The anxiety stems from the fact that astronomy, especially space-based astronomy, is just plain expensive. And with federal budgets tightening, the government will be less and less able to make huge investments in big science projects. "We may see in the next decade or so an end to the search for the laws of nature which will not be resumed again in our own lifetimes," warned Nobel Prize-winning physicist Steven Weinberg in January during the American Astronomical Society meeting in Austin, Texas."

"When you hear about a volcano erupting, what do you think is going on? If you're like us, you think of red hot chunks of rock being hurled thousands of feet in the air, flows of liquid magma, and plumes of smoke. That's not always the case. Some volcanoes erupt underwater and their smoking hot by-products are immediately cooled. With the Storm in a Cup, you can see what happens underwater on a smaller, safer scale."