Sky watch: Interstellar dust forms 'zodiacal light'

One of my least-favorite household chores is dusting.

If I let it go more than a week, I can write my name on my computer monitor, and not with keys either.

You've probably also noticed that when the lighting is just right, the dust is totally invisible. But when the light changes - usually moments before company arrives - the room appears aglow with dust.

The same thing is true in our part of the solar system. The entire inner solar system is littered with a thick dusty disk. And while this interplanetary cloud is composed of different stuff than what's on the stereo, the principles for seeing it are similar.

Since this dusty disk lies mostly in the plane of our solar system, that's where we can see it if the lighting is just right. And during the first two weeks of October, its faint pyramid of glowing light ascends almost vertically from the eastern horizon before sunrise. It's known as the "false dawn" or the "zodiacal light."

To see it, you'll need to rise long before the sun and head to the mountains or another "dark-sky" site with a clear view - and no city lights - to the east. Then, about 90 minutes or so before sunrise look for a large and softly glowing pyramid with its wide base in Leo and its tapered end above Gemini. Keep in mind that this glow is faint and any moonlight, haze or light pollution can make your effort futile.

This mysterious "false dawn" was described nearly a millennium ago by the Persian poet Omar Khayyám in his book "The Rubaiyat." Today we know it happens when sunlight is scattered from dust particles along the plane of our solar system. Most of these are generated by passing comets or collisions among asteroids; each is only about four-hundredths of an inch across and are separated by an average of five miles.

If you prefer to do your stargazing in the evening rather than at dawn, there's good news. The zodiacal light appears then too, but you'll have to wait until springtime to see it.