Jupiter Joins The Zodiacal Light Before Dawn

The long finger of zodiacal light points up over the Wisconsin shore in this photo taken this morning from Duluth, Minn. The "star" in the center is Jupiter, which casts a reflection on Lake Superior. Credit: Bob King
The long finger of the zodiacal light points up over the Wisconsin shore in this photo taken this morning from Duluth, Minn. The “star” in the center is Jupiter, which casts a reflection on Lake Superior. The first hint of the approaching sun reddens the horizon. The photo was taken about 95 minutes before sunrise. Credit: Bob King

To calm my mind on Election Day morning, I took off before dawn for Lake Superior. Just a quick hop to a beach 10 minutes from home. There along the silent shore stood a slanted feather of comet dust dotted by the bright planet Jupiter. Winds were light, so Jupiter left a gleam line on the water.

The time was 5:20 a.m. just before the start of dawn. By 5:30, a gathering of low clouds below Jupiter showed in silhouette against the faintest of oranges along the southeastern horizon. What a joy to watch night give way minute by minute to dawn. Watching a transition that’s been happening across the planet for the past several billion years dialed back my personal speedometer. Way back. This show’s been going on for more than 4 billion years. Reconnecting with ancient cycles sends becomes our personal time machine.

Dust shed from the tail and coma of Comet Giacobini-Zinner is responsible for the Draconid meteor shower. Credit: N.A.Sharp/NOAO/AURA/NSF - See more at: http://astrobob.areavoices.com/2012/10/06/draconid-meteor-shower-may-spice-up-weekend-sky/#sthash.M0h8GBBZ.dpuf
Dust shed from the tail and coma of comets such as 21P/Giacobini-Zinner, pictured here, keeps the zodiacal light replenished century after century. Credit: N.A.Sharp/NOAO/AURA/NSF

Let’s look more closely at the scene. Dust deposited by passing comets and crashing asteroids gathers in the plane of our solar system out to at least Jupiter. Sunlight (hidden by the horizon) is back-scattered by the dust, which makes it glow in the dark before dawn. Since all eight planets lie nearly in the same plane, it makes sense to see Jupiter smack in the middle of the zodiacal light.

Notice the steep tilt of the light cone. This time of year, the solar system plane tilts strongly upward as viewed from mid-northern latitudes. That makes a faint phenomenon like the zodiacal light easier to see because its muted light isn’t absorbed by dust and haze that “thicken” the air at lower viewing angles. We have a few more dark mornings — through Nov. 12 — before the waxing moon pushes into the morning sky and drowns out the light’s faint signal.

The zodiacal light cone, which is centered on the Sun's path through the zodiac called the ecliptic, tilts upward in late October
The zodiacal light cone, which is centered on the ecliptic or plane of the solar system, tilts upward in early November. The ecliptic passes through the 12 zodiac constellations, the origin of “zodiacal” in zodiacal light. Map: Bob King, Source: Stellarium

You can start looking for the phenomenon about 2-2½  hours before sunrise, but the comet cone is best at the beginning of dawn or about an hour 40 minutes before the sun comes up. It’s a BIG finger — about six fists tall and two fists wide at the base. See that orange glow to the right? That’s light pollution seeping into the frame from the city. That tells you us that you don’t need pristine skies all around to see the zodiacal light. It just needs to be dark in the eastern quarter of the sky.


The entire face of Jupiter from March 18-22, 2016 using photographs taken by astrophotographer Damian Peach

Jupiter is also a celebrity these November mornings. You can enjoy its return with the naked eye, try to spot several of its brightest moons in binoculars (hint: focus sharply and look very close to the planet) or view it through a telescope. When I got home, I set up a scope for my first view of the planet this apparition, a term used to describe the time a planet is visible during the year. Two dark cloud belts and three star-like satellites came into view.

With that, I quietly unlocked the front door in the still-dark house and slipped back into bed ready for what the day might bring.