Comet PANSTARRS – Hit Me Baby One More Time

Comet L4 PANSTARRS on May 27 when Earth cut directly through the comet’s orbital plane giving us an edge-on view through the broad but narrow cloud of dust shed by the comet over the past few months. Click to enlarge. Credit: Martin Mobberley

If you’re looking for nature’s version of a straight-edge, look no further than Comet PANSTARRS. We had the opportunity to see its millions-mile-wide dust fan edge-on this weekend. Well, not all of us did. Moonlight spoiled the visual view but astrophotographers found ways around the moonlight to produce spectacular images.

Another view of PANSTARRS taken on May 28. The incredible tail gives the comet the appearance of a streaking fireball. The anti-tail measures about 7.5 degrees. Click for giant version. Credit: Michael Jaeger

Tail lengths estimates varied, but wide-angle amateur photos show it extending up to 16 degrees long. That’s 32 full moons side by side. The physical tail length captured in the photos is about 23 million miles (37.5 million km) long, but since it’s projected at an angle to its orbit, the full extent is considerably longer, likely approaching 93 million miles or the Earth-sun distance.

Too big for one photo, Jost Jahn took multiple pictures to create this mosaic of the PANSTARRS’ tail. Click to be taken to an interactive view. Credit: Jost Jahn

The beam-like tail is called an anti-tail because it points toward the sun in the opposite direction of a normal comet tail. It’s composed of dust particles shed over the past several months.

Not only do those bits of dust and rock line its orbital track, they also migrate outward into a vast sheet or cloud extending beyond PANSTARRS’ orbit. The short, broader tail is the normal dust tail, where dust particles are being pushed away from PANSTARRS in real time by the pressure of sunlight.

While the comet is still visible in 50mm binoculars in dark, moonless skies, the tail(s) will shorten and fade in the coming weeks as the distance between it and Earth widens.

Jupiter (left), Mercury (top) and Venus make an appearance between clouds over San Diego in this photo taken when the three were closest on May 26. Credit: Kevin Baird

Jupiter, Mercury and Venus are still clustered together low in the northwestern sky after sunset for the next few nights. My sky was mostly cloudy and I never got more than a glimpse of the three over the weekend.

Jupiter, Mercury and Venus framed by two apartment
buildings in Hamilton, Ontario Sunday night. Credit: Alex Sokolow

Others were more fortunate. Alex Sokolow saw them squeezed between two apartment buildings when the three were in their most compact arrangement on the 26th.

Even if you got hit with bad weather or circumstance this weekend, you can still see our planetary friends together the next few nights. Jupiter is dropping fast but passes closest to Venus tonight – the two will be just a degree apart.

Before Jupiter departs the scene it has its closest encounter with Venus this evening. This map shows the sky facing northwest about 30-45 minutes after sunset. Mercury’s about one “fist” high at that time. Created with Stellarium

Have you ever seen Mercury? If not, this is the best evening opportunity this year to do so for northern hemisphere sky watchers.

4 Responses

  1. caralex

    Thanks, Bob, for posting Alex’s photo from downtown Hamilton. He was delighted to see it!

  2. Norman Sanker

    Hey Bob,
    Aside from my inability to find PANSTARRS over the past several evenings, I have a question. Why does dust shed by the comet stay in its orbital plane instead of dispersing equally in all directions? I’ll look for Comet P again on May 31 and June 1 when it’s between two relatively bright stars, according to your chart. I want to see that anti-tail! Later.
    Blind Norman

    1. astrobob

      Hi Norman,
      It does gradually disperse into a more diffuse cloud. I believe the reason it holds together in a thin sheet is because the dust particles – for a time – share the comet’s velocity and are ejected in roughly the same direction. An analogy would be a garden hose with a narrow opening to let the water through creating a fine, narrow directional spray. Now move the hose through an arc (comet’s orbit) and you’ll create a sheet of water much broader than wide. If the water hung in the air instead of falling to the ground, you’d see the sheet.

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