Comets ISON And Encke Give The Gift Of Zodiacal Light

The zodiacal light tilts upward from the southeastern horizon through the constellation Virgo toward Mars this morning Nov. 8, 2013. The green squares show the locations of two of the morning’s bright comets –  ISON and 2P/Encke. Watch for the light starting about 2 hours before sunrise. Credit: Bob King

See that big finger of light in the photo? That’s the zodiacal light, a vast cloud of mostly comet dust gathered into a thick disk in the plane of the solar system. It glows for the same reason you see sunbeams across your bedroom when you open the curtain in the morning – sunlight reflecting off specks of dust.

Sunbeams, also called crepuscular rays, are a mix of cloud shadows and sunlight reflecting off atmospheric dust. Similarly, the sun reflects off comet dust to shape the zodiacal light. Credit: Bob King

In your room we’re talking earthly dust, but in the solar system, minute motes of comet dust behave identically. From super dark locations the wedge of zodiacal light tapers and fades into a band encircling the zodiac called the zodiacal band (hence the name). The brightest part – that big finger again – is nearest the sun and visible on November mornings extending from the horizon nearly to Cancer the Crab. Take a look soon because the  glare of the moon will hide starting around the 15th.

Current comets and those from ages past deposit the dust from their tails and comas as solar heating broils their surfaces, releasing gas, bits of gravel and plenty of powdery dirt.

Comet ISON on Nov. 6 shows a glowing greenish head or coma and pretty dust tail. Notice also two new very skinny tails just up from the head. These could be the start of the comet’s gas or ion tail. Ion tails are made of gas excited by the sun’s ultraviolet light. Credit: Damian Peach

Over time much of the dust spirals in toward the sun and gets zapped, but new comets like ISON, fresh from the distant Oort Cloud, keep it replenished with new material. I wanted to share this photo because I know many of you either have been or are planning to venture outside in the cold dawn to see our current crop of bright-ish comets. If you live where the sky is very dark, the zodiacal light is easy to see. Matter of fact, the bottom half of the cone is easily as bright as the summertime Milky Way and can interfere with observing faint objects including comets.

I don’t mind. It’s fun knowing that the very objects that create the light just happen to be winging through it right now, offering us a chance to see these flying fuzzballs’ contribution to something greater than themselves.

2 Responses

  1. wdsta1

    Comet ison was seen frm my back patio smoking a frojo..lookd like a big craft rather thn a personal opinion..THEY’VE ARRIVED!!!!((anunnaki1))

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