Your go-to guy for giant asteroid impact scares

Hearken, for I am going to teach you how to read the NASA Near Earth Asteroid Current Impact Risks page, and then you will know more than all the world's news organizations combined, for they are morons.

A "Potentially Hazardous Asteroid", or PHA, will frequently have several future close encounters with Earth in which an impact might conceivably happen. As more information comes in, the probabilities of these potential impacts will change, and some may disappear or appear.

The column labeled "Impact Prob. (cum.)" is the cumulative probability of all possible impacts by a given asteroid over the next 100 years. It is NOT the probability of the earliest possible impact by that asteroid. For that, you must go to the page for the individual asteroid and look in the "Impact Probability" column where it intersects the first row of numbers.

The funky Tom Ridge-like color coding (I am almost positive that it was the inspiration for Tom Ridge's threat scale, but it is considerably less nonsensical) is an attempt to convey how freaked out you should be by each individual possibility, based on a number of things (impact probability, how bad it would be if it happened, and, I think, how soon the most probable impacts are). For all potential impactors yet discovered, the answer is at worst "not very".

And if you want to worry about esoteric possibilities...

By the way, that NASA page holds many delights if you look at the really slim probabilities. Hey, how about this two-kilometer-wide asteroid? Chance of impact: about 1 in 2 billion. The sole possible impact date: May 19, 2006. That's so soon that if this turned out to be headed our way there's absolutely no chance we could do anything about it. Size and velocity: enough to do one hell of a lot of damage. The projected yield is 360,000 megatons TNT. This would devastate a huge region, and might even cause a global climatic catastrophe that would kill billions.

Of course, the chance that you'll get killed in a car accident tomorrow is way bigger.

Pictures of the Sun

The single best-kept secret at NASA, for some reason, is this Web page, which just lists in one place all Web sites for past, present, and future American space science missions (and others with some NASA involvement), many of them quite obscure. There is buried treasure in there.

My favorite sites for repeated visiting, and possibly the most underrated sources of cool-looking pictures in the space program, are SOHO and TRACE, a pair of telescopes in space that observe the Sun in wavelengths inaccessible from the ground.

SOHO is a European-American observatory that has been hovering around the L1 point between Earth and Sun since 1996, sending back pictures of the whole solar disc and the corona. There are pictures and movies sent back almost in real time. It's fun to watch the coronagraph record of a big mass ejection, especially when it comes right at us: a big blob of fire expands out of the Sun and then, zap, the picture fills with noise when it hits SOHO.

TRACE is a satellite that takes more magnified pictures of psychedelic and often as-yet-unexplained... stuff... happening in the lower corona. The project Web site is a bit chaotic, but some time spent digging around in there is worthwhile. It's a great source of fiery desktop pictures for your computer.

The pictures were even better a few years back at solar maximum (they've got archives), but there's always stuff going on.