The zodiacal light is widest and brightest near the horizon and tapers to a narrow cone as you look farther up. Be aware that it's really big — a fist wide at its base and nearly five fists high. If you've never seen it before, turn your head from side to side and "sweep" the eastern sky with a wide gaze.
It's no coincidence that Venus shines squarely within the base of the zodiacal cone. Both planet and dust cloud lie in the plane of the solar system and straddle the ecliptic, an imaginary circle in the heavens that defines that plane. The sun, moon and planets all travel around the sky on or near the ecliptic.
Comet NEOWISE and a firefly synchronize on a warm night this past summer. Comets are made of dusty, dirty ice. When warmed by the sun, the ice sublimes — goes directly from solid to vapor — and releases dust and gas into space. (Bob King for the News Tribune)
Comets provide much of the dust for the zodiacal light, spewing it by the ton when their dirty ices vaporize under the heat of the sun. The rest comes by way of asteroid collisions. The material settles in the plane of the solar system as a vast interplanetary dust cloud with particles similar in size to the minute droplets released when you cough.
The combined light of billions of stars too far away and too faint to see individually with the naked eye is responsible for the hazy appearance of the Milky Way. The similar-looking zodiacal light gets its glow from sunlight scattered off countless dust particles. As you'd expect, it glows brightest nearest the sun and fades with increasing distance.
The zodiacal light is centered on the ecliptic, an imaginary sky circle that passes through the 12 constellations of the zodiac. "Zodiac" gives the zodiacal light its name. In October the ecliptic meets the eastern horizon at a steep angle which brings the cone into good view. When the angle is low, as it is in early spring, the zodiacal light blends into the horizon haze. (Stellarium with additions by Bob King)
The ecliptic's steep angle to the eastern horizon at dawn during October and November "lift" the dust cone into clear view on dark, moonless mornings. In March and April, the ecliptic stands at a similarly steep angle to the western horizon, and the zodiacal light towers high in the western sky at dusk.
This 1.5-second exposure at ISO 12,800 captures part of the Starlink-12 satellite train passing below the Big Dipper this morning (Oct. 16). The Dipper stars are about magnitude 2; the Starlinks ranged from 3rd to 4th magnitude. (Bob King for the News Tribune)
While out enjoying the sky this Friday (Oct. 16) I also caught sight of the latest batch of Starlink satellites from the Starlink-12 mission which launched on Oct. 6. They'll be making additional morning passes from many locations in the coming days. To find out if and when they're visible from your house, go to Heavens Above and click the Change your observing location link. Then click on the Starlink passes for all objects from a launchlink on the left side of the page for a list of passes.
Above that list, click on the Launch bar to open up a drop-down list of Starlink missions, then select Starlink L12. You'll get a long list of passes with details about magnitudes, altitudes and times. Click any pass for a map showing its path in the sky.
The next launch, Starlink L13, is slated for Oct. 18. As of Oct. 7 SpaceX has sent 775 Starlinks into orbit, making it by far the largest satellite "constellation" in the sky. The company plans to begin offering high-speed, satellite internet service (100 Mbps download speed) to rural areas in Canada and the northern U.S. later this year for around $80/month.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.
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October 19, 2020 at 01:00AM
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Astro Bob: October mornings with the zodiacal light / Starlink satellite news - Duluth News Tribune
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