Jimmy Westlake: Spot the zodiacal light this week
The vacuum of space is empty, right?
Well, by earthly standards, yes it is, but it isn’t completely devoid of all matter. In fact, the space between the planets is filled with fine, powdery dust particles.
Much of this dust comes from the passage of comets through the warm inner solar system, but some also comes from pulverizing collisions between rocky asteroids. Astronomers estimate there is enough dust scattered through the inner solar system to build a couple of objects the size of the Martian moons, Phobos and Deimos — about 15 miles in diameter.
Each tiny dust speck follows its own orbit around the sun, just like a planet. If a dust particle hits the Earth’s atmosphere at high speed, it is incinerated in a quick streak of light called a meteor, popularly called a “shooting star.” On any given night of the year, you can see about five or six of these meteors per hour of sky watching.
The interplanetary dust also is visible to us in another much more subtle way. Just as a shaft of sunlight streaming through a window reveals motes of floating dust, sunlight scattering off of dust particles in space creates a faint band of light that can be seen right here on Earth, from very dark locations.
The glowing dust band traces out the ecliptic — the path that the sun, moon and planets, follow through the 12 constellations of the zodiac. This “zodiacal light” is visible as a pyramid-shaped glow that extends upward from the sunrise and sunset points on the horizon.
If sky conditions are good, the zodiacal light can be traced all the way up to the zenith. Its brightness is comparable to that of the glow of the Milky Way.
The dark of the moon in late February is the very best time of the year to see the zodiacal light in the evening sky. This is when the ecliptic and, with it, the zodiacal light, makes its steepest angle to the horizon, sticking nearly straight up. Look west, just as darkness arrives around 7 p.m.
This Friday evening, Feb. 20, will be an excellent time to step out and spot the zodiacal light, when the thin crescent moon joins planets Venus and Mars for a very close conjunction. All three will be deeply immersed in the light’s opalescent glow. The tapering shaft of zodiacal light should extend up to the twinkly Seven Sisters star cluster and beyond.
Many casual sky watchers likely have seen the zodiacal light and dismissed it out of hand as the atmospheric glow of the setting or rising sun. Indeed, the zodiacal light has earned the nicknames of “false dusk” and “false dawn.” Moonlight, haze or the glow of city lights will render the delicate zodiacal light invisible.
Consequently, most folks, including many astronomers, have never seen it.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy’s astrophotography website at http://www.jwestlake.com.
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Yampatika, an environmental education nonprofit based in Steamboat Springs, will host its 22nd annual Wild Edible Feast on Thursday evening, May 26, at Aurum Food & Wine.