Sciency Words: Tau Level

Today’s post is part of a special series here on Planet Pailly called Sciency Words.  Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

TAU LEVEL

I first came across this term in a press release from NASA’s Jet Propulsion Laboratory.  It has to do with Mars, and the global dust storm that’s been happening there these last few months, and that Mars rover that we may have lost.  But most of all, this tau level thing has to do with Beer.

No, not that kind of beer.

I’m talking about Dr. August Beer, a 19th Century German physicist who studied how light passes through and/or gets absorbed by various substances.  Dr. Beer is best remembered for Beer’s law, which (according to several papers I looked at… click here or here or here) is used to calculate how much sunlight makes it through the Martian atmosphere to reach the planet’s surface.

In those calculations, the Greek letter tau (τ) represents the amount of dust or other particulate matter that’s floating around in the atmosphere.  The more dust in the air, the higher the tau level.  And the higher the tau level, the less sunlight reaches the ground.

As you can imagine, you need to measure the tau level on Mars each day (or rather, each sol) and predict what the tau level will be tomorrow (I mean, solmorrow) if you’re trying to run any sort of surface mission on Mars that depends on solar power.  And in the future, when we have a well-established colony on Mars, don’t be surprised if the term tau level features prominently in the local weather reports.

P.S.: I had an idea that got too convoluted, but I really wanted to make a “don’t drink and drive” joke involving Beer’s law and our possibly wrecked Mars rover.

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