Of Comets and Contrails

Full frame image taken by E Warner on 26 Oct 2013 from Alexandria, VA.
(With dust spots on my sensor included!)


On any given clear day, we can usually look up and see an airplane or two way up high in the sky. If the conditions are right, they might have a long streamer, a contrail, trailing behind. And when they're directly overhead, it's easy to recognize them as airplanes with contrails. Some planes may form contrails and some in other parts of the sky may not.

But what happens if there is an airplane way far away closer to the horizon with a short contrail? The airplane may not even be visible because it is so far away and the contrail might look brighter than usual because it is reflecting light from the setting or rising sun. But it is still an airplane with a contrail.

We've been getting reports of observers seeing comet ISON in the evening sky. Unfortunately, the comet is in the morning sky right now (late October, into November) and is still too faint to be seen with just your naked eye. What most people are seeing are airplanes with contrails. I went out on the evenings of 26 and 27 October and took lots of pictures. The one at left shows 4 airplanes with obvious contrails as well as a number of older, dissipating contrails (the streamers left in the image down near the horizon). You can click on the image to get the full size version.

Below are images zoomed in on the individual airplanes from left to right. (All images taken with a Canon 20Da with a 28-135mm lens set at 38mm for the wide angle above and 135mm for the zoomed in shots below.)

Left most airplane above the dissipating, older contrails.
Bright one left of center.
Right most airplane with contrail.
Faint one up and left from the Masonic Memorial.

Those certainly do vaguely resemble what some people imagine comets to look like. And we have had comets bright enough to see in the twilight sky. Most recently comet PanSTARRS in March 2013 and before that comet McNaught, which although quite spectacular in the southern hemisphere, was just barely (!) visible as a smudge in the evening twilight in Jan 2007 in the northern hemisphere.

C/2006 P1 (McNaught)

Comet McNaught imaged 8 Jan 2007 from Alexandria, VA with a 28mm lens.
Comet McNaught imaged 8 Jan 2007 from Alexandria, VA with a 400mm lens.


Comet PanSTARRS imaged 12 Mar 2013 from College Park, MD.
The comet is visible to the left of the Moon.
Comet PanSTARRS imaged 13 Mar 2013 from College Park, MD.
The comet is down near the tree line. There are some faint stars visible between the comet and Moon.

Telling them apart

To be honest, there is no absolute way to distinguish comets and far away airplane contrails apart. Usually, the airplanes will move over several minutes. And they can move in any direction. Comets will seem to move because of the Earth's rotation. (Yes, they do move through the sky, so from one night to the next you'll notice a slightly changed background of stars, but the gross motion is because of the Earth's rotation.) They'll rise if they are in the East and set if they are in the West. It helps to have binoculars because then you might be able to see the airplane at the tip of the contrail. A comet on the other hand will usually be brightest at the head and fainter in the tail.

Image Credits

All images on this page of the contrails and comets were taken by Elizabeth Warner.

Keep up-to-date on the the Amateur Observers' Program (aop.astro.umd.edu) comet news via my @cometexplorer Twitter feed. All opinions stated on there, and in my blog posts, are my own.