While comets can't tell lies, they do sometimes grow long noses. As the weeks click by and our perspective on Comet L4 PANSTARRS changes, its original plume-like dust tail has shrunk and faded while a second tail just won't stop growing. I'm talking about the anti-tail, so called because it points toward the sun instead of away. Like the normal dust tail, an anti-tail is formed from fresh dust blown back from the comet's head by the pressure of sunlight. As the comet continues along its orbital path, last week's dust lingers behind, forming a "trail of breadcrumbs" in its wake. Right now those breadcrumbs look like a light saber straight out of Star Wars. Time exposure photographs show a striking sunward-pointing appendage more than 6 degrees (12 full moons) long. I've been keeping an eye on Comet PANSTARRS here at home and can report that the anti-tail is plainly visible with a telescope under dark skies. Watching it grow from a short nub to the most dominant feature of this remarkable object has been the highlight of many a clear night.

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© Damian PeachWow – that’s a tail! Comet C/2011 L4 PANSTARRS on May 21, 2013, when its anti-tail (left) had grown to more than 12 full moons in length. Meanwhile, what was once the main dust tail (right) has faded and shortened over the past few weeks.

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© NASA/JPL/my own additionsOur current “edge on” view of Comet PANSTARRS is similar to looking down on it from high above the Earth’s north pole, where the dust stacks up to create a bright, streak-like tail.

Nothing stands still in our solar system. Earth's moving, the comet's moving. Later this week on May 26-27, Earth will pass directly through the comet's orbital plane, which slices through the plane of the planets at a very steep angle. As the Earth approaches this intersection, we look up (from the northern hemisphere) and stare squarely into the long trail of dusty debris deposited by PANSTARRS during its recent swing around the sun in March. It gets better.

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© Michael JaegerIf we step back in time to May 9, we see that the anti-tail was neither as long nor as pronounced because the Earth was further from the comet’s orbital plane. Because we were more broadside to the comet then, the dust sheet is much more obvious. It extends millions of miles into space but is only 5,000-10,000 miles thick.
Sunlight pushes the smaller particles into a vast, thin sheet or fan extending millions of miles into space well beyond the path traveled by the comet's nucleus. Since we now see PANSTARRS almost "edge-on", all that dust overlaps from our perspective to form a thick, bright line sticking out of the comet's head. It's as if we're seeing the ghost of PANSTARRS from the recent past still lingering in space. If we could somehow see the whole works broadside, the comet would appear fainter, spread out and much more diffuse.

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© Bob KingSimulated views of dust shed by PANSTARRS’ in its orbit around the sun. Dust piles up in the edge-on view to create a skinny, saber-like tail vs. a faint, broad tail (right).
The Milky Way stands out as a band of light distinct from the thin scree of stars for the very same reason; our gaze cuts edge-on through our galaxy's flattened disk where stars are most concentrated. Like comet dust, they pile atop one other to create a distinct ribbon of fuzzy light slicing across the night sky.

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© Michael JeagerGoing back even further to April 10, the anti-tail (short stub to left of bright head) was just getting started. It’s completely dwarfed by the comet’s main dust tail and fan of tinier dust particles. Compare this photo to the current view.
In the next few days the tail could grow considerably longer and intensify in brightness as we move closer to the comet's orbital plane. Unfortunately the moon will be at or near full at the same time, making it tougher to fully appreciate this amazing apparition at least with binoculars and telescopes. Cameras will have better luck. Will that stop you from looking? I hope not. Either way, you can use this map to help you find Comet PANSTARRS and check it out yourself.

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© Created with Chris Marriott’s SkyMap softwareMap showing Comet C/2011 L4 PANSTARRS’ location tonight through June 21. Positions are marked off every three nights with stars are shown to about 8th magnitude.
When you do spot the anti-tail, don't be fooled. It may appear to be pointing at the sun, but it's only dust spread along a path once tread.