Alan Stahler: Overhead tonight will be a glimpse of the Space Station |

Alan Stahler: Overhead tonight will be a glimpse of the Space Station

Alan Stahler

The “cat” in “cat-scan” is an acronym — a word made from the initials of other words; it stands for computer-assisted tomography.

An X-ray image is a shadow-picture. X-rays are a lot like visible light: Both are forms of electromagnetic radiation. But medical X-rays have way more energy — enough energy to zap through muscle and fat, like light through a window … but not enough energy to go through bone, which casts a shadow.

A cat-scan is made by X-raying the body from many different directions. A computer looks at the shadow-pictures, taken from all sides, and calculates what a thin slice of the body would look like, from above … as if you could slice the body like a salami.

Tomography is the technique of making pictures of slices … without the unfortunate side-effects that would result from slicing a patient like a salami.

Add the letter “a” to a word and you change it into its opposite: Bacteria that reproduce without sex are asexual.

For thousands of years, philosophers wondered about the building blocks of which the world is constructed. Suppose you had a block of silver, and sliced in half … and then, in half again, and again, and again. Eventually, they proposed, you would end up with the smallest particle of silver possible — one that could not be further sliced. They called this un-sliceable building block an atom.

They were right … partly. Once you’re down to a single atom of silver, you cannot slice it further and still have silver. But that doesn’t mean you can’t keep slicing, dissecting the atom into sub-atomic particles: protons, neutrons and electrons. Protons and neutrons reside in the nucleus, in the heart of the atom; electrons whiz about in a cloud surrounding the nucleus.

It’s not hard to pull electrons off an atom: walk across a rug, pet a cat, doff a sweater, and you scrape electrons off atoms.

Scraped-off electrons really want to get back onto atoms … give them a chance, and they jump between your hand and a doorknob.

We take advantage of the desire of electrons to get back onto their atoms, by allowing them to recombine … but only after they’ve done some work, driving our electrical appliances, from toasters to tablets.

Electrical generating stations have a number of different ways to separate electrons from their atoms. Most common is to spin a coil of wire through a magnetic field. The coil might be spun by steam, or by fast-flowing water, or by wind.

Or — like green plants and pond-scum — we could pull electrons of atoms using the energy of sunlight. (Rather than harness those electrons to do work, plants and pond-scum attach those electrons to other atoms, creating molecules of sugar, which store energy for later use.).

The International Space Station is powered by photovoltaics — over a half-acre of solar panels.

Covered with glass, solar panels reflect a lot of sunlight, which will make the space station easy to spot tonight (Wednesday). Rising in the northwest at 9:11, heading toward the southeast, the station will climb higher, until, a minute or so later, it will be right overhead.

In the late 1600s, Isaac Newton proposed that, were a cannonball fired fast enough, it would never hit the ground; rather, it would orbit the Earth forever.

Traveling a bit over 17,000 miles per hour, the Space Station (crewed by six astronauts: two women, four men) circles the Earth in just-over an hour-and-a-half.

Al Stahler enjoys sharing nature with friends and neighbors. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at

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