Science

In Early March, Look To The West For The Zodiacal Light!

Not too many years ago, astronomers thought there were chunks of space where there were no stars. Now we know that the zodiac is fairly uniformly filled with stars — but that a phenomenon called cosmic dust can block our view of them.

Cosmic dust is primarily made up of tiny particles that are debris that didn’t coalesce into planets or other celestial bodies during the formation of the solar system. The particles range in size from microns (and less) to meters (and more). A disk-shaped cloud of these particles extends from the sun to past Mars’ orbit. Estimates of how much of this dust actually enters Earth’s atmosphere and falls on the Earth vary. They seem to range from 5 to 300 metric tons per day. (Yes, that’s an order of magnitude discrepancy. And, no, even at 300 metric tons, that’s not enough to throw Earth off its orbit. It’s an almost insignificant amount compared to the weight of the planet.)

The disk-shaped cloud itself lies roughly along the ecliptic, which is the imaginary line traced by the sun in its annual arc across the sky. (The sun, of course, doesn’t move across the sky. But it seems to from our perspective, as Earth slowly rotates.)

During these early weeks of March, Earth is at such an angle to the cloud that, if you’re in the northern hemisphere, you might be able to catch a beautiful glimpse of the dust even without a telescope. This is courtesy of a phenomenon called the “zodiacal light,” in which the sun (from behind the curve of the Earth) illuminates the dust hanging in a dark sky. To see it, about 60-90 minutes after the sun has set look west (or maybe southwest; it depends on how far north of the equator you are). If there is no incidental light pollution, the horizon will glow and a hazy, white pyramid of light will reach up into the stars.

If you’re in the southern hemisphere this March, look for the zodiacal light an hour or so before dawn. On or near the equator, the light can be seen before dawn and after dusk throughout the year.

Even moonlight might brighten the sky enough to make the zodiacal light invisible. Rumor has it, though, that a slight, rising crescent moon can be a miraculously beautiful addition to the zodiacal light.

LumenlearningAstronomy


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