Tunguska Event may have been caused by a comet

Today I came across an article published on June 25th, 2009 that may explain what really did happen in the Tunguska region of Russia in 1908 (I mentioned the Tunguska event in my article titled "Fire, Brimstone, and Bombs Oh My!"). The evidence comes from a space shuttle's exhaust plume that resembled the effects of a comet. According to the article posted on Sciencedaily.com:

The research, accepted for publication (June 24, 2009) by the journal Geophysical Research Letters, published by the American Geophysical Union, connects the two events by what followed each about a day later: brilliant, night-visible clouds, or noctilucent clouds, that are made up of ice particles and only form at very high altitudes and in extremely cold temperatures.

"It's almost like putting together a 100-year-old murder mystery," said Michael Kelley, the James A. Friend Family Distinguished Professor of Engineering at Cornell who led the research team. "The evidence is pretty strong that the Earth was hit by a comet in 1908." Previous speculation had ranged from comets to meteors.

The researchers contend that the massive amount of water vapor spewed into the atmosphere by the comet's icy nucleus was caught up in swirling eddies with tremendous energy by a process called two-dimensional turbulence, which explains why the noctilucent clouds formed a day later many thousands of miles away.

Read the rest of the article here. I still wonder though....nobody saw this? I would think if a comet was hurtling towards the Earth that someone would have seen it. I understand that observational equipment wasn't as good back then and that the area where the event occurred was unpopulated, but, considering the Earth rotates, I thought it would have been visible by someone in a populated area looking at the sky shortly before it hit.