Category: Astronomy

(This is the fourth post in a series, though it can be read independently; here are post #1 , post #2 , and post #3.)

For many years, I thought that measuring the distance to the Sun was quite difficult for a non-astronomer. I had the impression that it requires precision measurements, often involving telescopes or information from satellites, and that it was only easy to obtain a minimum distance and a maximum distance that were still quite far apart, as I explained in my last post.

But it’s not true. As I’ll explain today, it turns out that anyone can estimate the distance to the Sun, at night, with nothing more than the naked eye, basic reasoning, and… meteors.

Just from the fact that a long meteor crosses the sky in a few seconds, you can infer that the Earth-Sun distance is something like 100 million miles (km). If the Sun were only 10 million miles (km) away, the meteors would lazily drift among the stars, only a bit faster than the motions of the space station and other satellites, which take minutes to cross the sky. Meanwhile, if the Sun were a billion miles (km) away, then meteors would flash across the sky in a fraction of a second.

With a little more work and knowledge, you can use meteors to make an estimate of the Sun’s distance that’s well within a factor of 2 of the truth. It’s not even that hard to get a precise measurement that’s good to 10% or so.

It may seem odd that one can use such little specks of dust in the Earth’s atmosphere to determine, without a telescope, how far it is to the Sun. But in fact the method is simple. It’s so simple that it must have been pointed out two centuries ago. Curiously, though, I’ve never seen it written down anywhere. It seems to be little-known, even to scientists.