STEREO beams back stunning new PANSTARRS pics

STEREO-B photo of Comet PANSTARRS along with planet Earth taken March 13 and processed by Alan Watson. The two vertical white lines are electronic artifacts. Credit: NASA

I thought the first STEREO-B pictures of C/2011 L4 PANSTARRS joined by planet Earth were sweet enough enough. No, no. This one – and the accompanying video – are far nicer. They were made on March 13 when PANSTARRS had more fully entered the telescope’s field of view.

STEREO-A and STEREO-B are twin NASA space probes that study the farside of the sun invisible from Earth stereoscopically. They orbit ahead and behind our planet in its orbit. STEREO-B looks back toward the Earth and comet from its current position in orbit. The diagram show the inner solar system viewed from above Earth’s north pole. Credit: NASA

Relish the many plumes striping the comet’s broad dust tail. Astronomers call them “striae” (STRY-eye or STRY-ee), and they result from the release of massive amounts of dust from vaporizing cometary ices. As they’re blown back by the pressure of sunlight to form the tail, the particles get sorted out into individual plumes according to their varying sizes. Let’s hope that once PANSTARRS gets high enough to see in a darker sky, the beautiful striae will reveal themselves.


STEREO-B video of Comet PANSTARRS and a blast from the sun

The video was compiled using multiple single frames from STEREO-B. The field of view is about 20 degrees (about as wide as the constellation Orion is tall) and the sun is out of the field of field. STEREO-B orbits on the opposite side of the sun from Earth and looks back toward the comet which is fortuitously lined up with the Earth. Amping up the excitement another notch, a coronal mass ejection from the sun appears to be headed for the comet. This is a trick of perspective – the blast missed PANSTARRS by some distance.


Another animation of the comet from March 13 STEREO-B images. Sun is off to the left.

Speaking of distance, you’ll see in the lower left of the orbital diagram that STEREO-B is 1.9 A.U. from Earth. An A.U. or astronomical unit is equal to Earth’s distance from the sun or 93 million miles, so the spacecraft is currently about 177 million miles from our planet. PANSTARRS meanwhile is 1.1 A.U.s from Earth (102 million miles) and very approximately 75 million miles from STEREO-B.

Heads and (many) tails. Comet PANSTARRS on March 15 from Valley Forge National Park, Penn. Credit: John Chumack

I only toss these figures out so you can appreciate the enormity of the comet’s dust tail. The Earth barely registers as more than a blip in the picture. Even accounting for PANSTARRS being some 40% closer to STEREO’s camera than Earth, the tail measures at least a million miles long. Compare that to Earth’s 8,000-mile-diameter and you can begin to appreciate its size.

Comet Hyakutake, which was strode across the spring sky in 1996 had one of the longest tails on record: 354 million miles (570 million km). Credit: NASA

Since comet tails aren’t solid objects, the amount of mass they contain is very small despite appearances. Indeed, they put on a good show!

Comet Hyakutake

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

8 thoughts on “STEREO beams back stunning new PANSTARRS pics

  1. Hi dear Bob.. Also I got the comet.. Already on 12th. It was difficult because of clouds. We had many days of overcast. One day at sunset a hole opened, just in line with the comet coordinates. But the telescope revealed that the hole was just lighter clouds.. Then suddenly a white point appeared in scope: the comet was so bright that its light pinched through the clouds, quite like a bright star. The photos revealed also the tail http://postimage.org/image/6gyov5g4z/

    Today I saw it again, still battling clouds, but could see the tail.
    With better weather we’ll see it better.
    Clear skies!

  2. Wow the Stereo B images are fantastic. It really puts the comet into perspective and that Sun blast was crazy. Will PanSTARRS leave a dust field Earth will pass through creating a new meteor shower?

    • Tim,
      Great question. I don’t think PANSTARRS’ orbit is such that we’ll be passing through its dusty debris anytime soon. It’s very steep. The comet came up from below the plane of the solar system, sliced through the plane inside the orbit of Mercury and is now moving in a steep curve above it. Earth’s too far from all the action, and the tail, which points away from the sun, now points up and way from the plane of the planets.

  3. Hi Bob,
    I sent you an e-mail, hope you don’t mind and be able to reply when you get a minute as I know your very busy. Thanks

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