Why we can sometimes hear the northern lights

If you're getting sick of astronomy, just scroll down!

I went out to the Tucson Amateur Astronomy Club's viewing site tonight, about 15 miles west of Tucson in a remote part of the desert. I went there last year as well, and was treated to some good views on the many telescopes. Tonight there were fewer scopes set up; the moon is at 25%, which blocks out a lot of the more remote objects, and scares off the astronomers who don't want to stay up late enough for the moon to set.

I brought my binoculars and was treated to a great view of the Andromeda galaxy, once it was pointed out for me by a man with one of those laser beam flashlights. I practiced finding it several times so that I can find it when I get home. Saturn was wavy tonight, they said, although I thought it looked plenty nice. You couldn't see the gaps in the rings, which is sort of the standard for Saturn viewing.

Astronomers are a nice bunch, always eager to tell you what they know. I spent most of my time tonight at the telescope of a man who is working his way through a particular catalog of 400 sky objects. Tonight, he was hoping to locate and draw sketches of about ten of them. I stayed for two, and then I got cold--the thermometer on his scope said 33 degrees! The man had snowpants on, but I wasn't so well wrapped and got frozen to the bone.

I did see some great views of the Orion Nebula through two separate scopes. One man was hoping to sell his telescope, so I got the pitch. I guess that is a hazard of attending star parties. He showed me several star clusters, some of which I could see through my binoculars as well.

Also saw a galaxy which is facing us directly. The spiral arms are sometimes in view, but tonight the moon's light made the arms of the galaxy difficult to see. Tonight, that galaxy was little more than, to use their term, a "ball of cotton."

Sat in the pickup a while to warm up, and a British man joined me, an astronomy professor. He pointed out that the Big Dipper was rising in the north. In Minnesota, the Big Dipper never sets, but here it sinks below the horizon. The term for such phenomena is circumpolar, meaning that in Minnesota the Big Dipper is circumpolar while in Arizona it is not. In Minnesota, because we are so far north, there is a larger circle of stars which never sets than there is here in Arizona.

You almost never see northern lights in Arizona, so I bragged up our views of aurora borealis up north, and added that I had once actually heard them.

Well, one astonomer said, what time of year was it? Were there leaves on the ground? I said I didn't remember.

So, he taught me something new: Meteorites also were known to make noise when they fall, a sort of buzzing or rustling. However, astronomers could never record or measure the sound when they aimed dishes at the meteorites--they really wondered if it was real.

To make matters more strange, the noise made by a falling meteor was instant--it sounded right when the meteor streaked through the sky. Impossible. Sound travels slowly--even a lightning bolt one mile away makes thunder which sounds several seconds later. A meteorite can be 100s of miles away--there is simply no way the sound could travel that fast. So, the sound must be an illusion, they thought, perhaps a case of wishful thinking.

However, somebody noticed that falling stars only made noise when there were fallen leaves on the ground. Turns out, meteors emit a particular low frequency radio wave. That same somebody put two and two together, hauled a pile of leaves into a laboratory and bombarded them with this particular frequency of radio waves. Sure enough, there was a measurable, audible rustling! Mystery solved.

Turns out, my memory of the noise made by northern lights was that the buzzing was simultaneous with the flashes of light. I never thought at the time about sound traveling too slow for it to come directly from high in the atmosphere. My experience hearing the northern lights, therefore, must have been on a still night in the fall when there were dry leaves on the ground.

Uffda, the crazy things we can learn.