Dust! We can’t live with it or without it. We wipe it off, vacuum it up and try not to breathe it. Yet it carries our rain, allows for colorful sunsets and sunrises and puts smoke in our chimneys. Dust also is all over the universe and gives us the wonder of zodiacal light in our late winter evening sky.
Orbiting with the planets of the solar system is a vast band of minute dust particles; the planets are said to have arisen from dust coming together. An untold number of comets, made of dust, ice and gas, loop around the sun. As comets near the sun, and the icy nucleus melts, dust is released. The delicate pressure of sunlight pushes dust and gas back in the incredibly long tails some comets sport, the rare bright one capturing the public’s notice. Those cometary particles give us meteors. Crushed astroids add to the dusty planetary veil.
The great spread of dust in the plane of the solar system can under the right conditions, be seen by the unaided eye against the starry sky following sunset or before sunrise.
It’s called zodiacal light because the dust, along the plane that all of the major planets roughly follow, is traced on the sky where it is often called the “zodiac.” The path of the planets, moon and sun is also known as the ecliptic.
We most easily witness this phenomenon in the western sky after sunset or in the eastern sky before sunrise, because this is where the dust is closer to us and the reflecting sunshine, and the dust is thicker.
You need a very dark site to see it, away from the light pollution of cities and towns, and when there is no moonshine. If the hazy, dim Milky Way band is easily visible, you are more likely to see the zodiacal light. It appears even “milkier” than the Milky Way.
Although always present, it is best seen at certain times of the year when the ecliptic makes a steep angle with the western horizon on February, March and April evenings, as seen from the Northern Hemisphere. It is likewise best seen in the morning before dawn, in late summer and early fall.
The light appears when the evening twilight has left the sky, around 80 to 120 minutes after sundown.
I had a wonderful view of the evening zodiacal light one time, coming home on an airliner from Florida in March. I had a west-facing window, and had to cover my head with my jacket (the flight attendant wasn’t looking) as I peered from my plane seat observatory some 30,000 feet up. The zodiacal light was astonishingly bright, and formed a long, slanting triangle from the horizon of the Gulf of Mexico, reaching towards the Pleiades star cluster.
This dusty band actually traces all around the sky along the ecliptic, but is much fainter to see. From very dark, remote locations, one can sometimes detect a ghostly dim patch of light opposite (180 degrees from) the sun, visible around midnight when the ecliptic arches highest in the sky. This is called the gegenschein, German for “counter glow.” This patch of light is part of the band causing the zodiacal light and is noticeable because each tiny dust grain is, in effect, a “full moon” shining back at us with the maximum amount of sunlight.
Although the zodiacal light is so hard to see where most people live, we have the constellations of stars and planets to keep us busy when we venture out to see the heavens above.
Beyond our solar system, dust makes up the nebulae, great swirls of cosmic clouds. The Great Nebula of Orion, where stars are forming, is a well-known example. Amateur astronomers make great sport seeking out these faint, interstellar dust bunnies with a telescope.
This year we have the brilliant planet Venus shining in the west, adding to the scene, and that heavenly sight is visible even from a city.
Last quarter moon is March 16, and new moon is March 24; the moon doesn’t return to the evening sky until after March 24.
Keep looking up at the sky!
Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at [email protected] Please mention in what newspaper or website you read this column.
Discussion about this post