Unsound
May 11, 2026 at 2:17 PM by Dr. Drang
I mentioned last week that some wording in a news article struck me as odd. A similar thing happened when I read this Scientific American piece (that’s an Apple News link—I don’t have a SciAm subscription). In this case, I didn’t even have to read the article; the oddity is right there in the headline: “A SpaceX rocket booster is on track to hit the Moon at several times the speed of sound.”
I know what the writer means, of course. He’s telling us that the SpaceX debris will hit the Moon at several thousand feet per second, 1,000 fps being about the speed of sound we’re used to here on Earth. But the Moon isn’t the Earth, so it’s kind of a weird comparison, don’t you think? It’s not as if the booster is going to create a sonic boom. I’d find this less odd if the story were in a normal newspaper or magazine instead of Scientific American.
Again, I realize that the writer is just giving his readers a point of comparison, but is the speed of sound (on Earth) really something most people have an intuitive feel for? I remember learning as a kid to count off the seconds between a lightning flash and the resulting thunder to get the distance to the lightning strike in thousands of feet, but that doesn’t mean I have a strong sense of the speed of sound. Other than “really fast,” which isn’t all that helpful.
It’s mentioned in the body of the article that the speed of the booster at impact, which will be on August 5, is estimated to be about 5,400 mph. That’s about 100 times the posted speed limit on a two-lane highway, which is something most Americans do have a feel for.
By the way, if you have any interest in the problem of space debris coming back and striking the Earth (where the speed of sound might be relevant), you should follow Sam Lawler on Mastodon. She’s a professor of astronomy at the University of Regina and also has a keen interest in the clogging of near-Earth orbital space by the huge number of satellites launched in recent years. Her Mastodon feed is also a great source of farm animal photos, most recently a crop of baby goats.