Attending mass

Bad Astronomy
The entire universe in blog form
Dec. 2 2007 12:50 PM

Attending mass

Does a star mass?

I sometimes use the word "mass" as a verb, like, "That star masses 20 times that of the Sun". I know it sounds funny, but astronomers say it that way all the time. My friend Cindy Taylor, also an astronomer, took me to task for this some time ago. She thinks we shouldn't use it that way.


She has a point. I wouldn't say "The car lengths 2 meters", so why would I say "The car masses 1500 kilograms"? The problem is, we don't have a good verb for "mass". We can say "the car weighs 3000 pounds, " but what do we use for kilograms?

This brings up the whole mass versus weight issue, and whether you can use kilograms as a weight (I think it's OK as a shorthand if it's understood this is in one Earth gravity; on the Moon the weight is less but the mass is the same, so it can be confusing). But even without that added complication, what do we say when a star has a mass of 1030 kilograms? I guess we say it just like that: The star has a mass of 1030 kilograms. As an astronomer I suppose that's fine, but as a writer I have an issue with that: it's limiting. I need to use synonyms sometimes, or else things get boring. There is something a little more poetic in saying "The star masses 1030 kilograms." It's more adjective-friendly, too: "The star masses a whopping 1030 kilograms." Cool!

English is many things, but one of its more endearing qualities is that it's fluid. It changes, adapts, evolves. Slowly, sometimes, but inertia is a property of not just mass. So maybe it's time for English to take this tiny step forward, and learn how to mass.

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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