Archive for category Comets

Coming up: Comet ISON in November 2013

You may have heard of Comet ISON, a comet discovered last year that is currently approaching the Sun. It is expected to be visible in the SOHO-LASCO C2 and C3: from SOHO’s viewpoint the comet enters from the lower right early on November 27 and exits towards the top near the end of November 30 this year.

Path of COMET ISON as seen from SOHO

Path of COMET ISON as seen from SOHO LASCO C2 and C3 coronagraphs.

It will also be visible from the COR1 and COR2 instruments on board both STEREO spacecraft. The SOHO Hotshot webpage for Comet ISON has many more links to more details on the path of the comet as seen from SOHO and STEREO. At the moment it looks like this, as seen by the Hubble Space Telescope. It might be a spectacular sight from Earth. The appearance of comets from Earth is hard to predict because how it looks when it gets closer to the Sun depends on the details of its composition. We’ll have to wait and see!

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Comet Lovejoy – special observations coming up.

Comet Lovejoy will be passing close to the Sun in the next couple of days. SDO will be taking special observations of the comet beginning 22:59 UT on 2011/12/15 (5.59pm 2011/12/15, Eastern Time), and lasting for a couple of hours. The comet will pass behind the solar limb at around 00:07 UT 2011/12/16 (7:07pm 2011/12/15, Eastern Time). There is a chance the comet will survive its encounter with the Sun.

SDO/AIA will take special observations to view the comet; AIA will change its pointing and point slightly away from the center of the Sun in order to try to get more observations of the comet as it gets close to the disk of the Sun.

Why are these observations being taken? Well, we are looking for something like we saw on 2011/07/05 this year. On that day a comet fell in to the Sun. These kinds of comets have been seen before in LASCO-C3 and LASCO-C2 images. What was new about this observation was that for the first time the comet was seen against the disk of the Sun. The video below gives a description of what was seen.

SDO/AIA detects different wavelengths of light. So in order for us to see it, the comet must have been emitting at those different wavelengths, and the comet must have disintegrated in to a big enough cloud of ionized gas for us to see it. So the big scientific question about seeing this comet against the disk of the Sun is explaining both how it came to be emitting at wavelengths that SDO/AIA could see, and figuring out how it could have disintegrated. This is an active area of research, with presentations on this subject given last week at the American Geophysical Union‘s Fall Meeting, and a paper set to appear in Science.

Comet Lovejoy is already visible. YouTube and user otraLoly posted a video earlier on today of Comet Lovejoy entering the field of view of LASCO C3.

We hope you enjoy tracking Comet Lovejoy as it gets closer to the Sun. Please let us know if you have any further questions about the Helioviewer Project and Comet Lovejoy.

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User highlight: comet in LASCO-C2

YouTube and Helioviewer.org user galaxy387 posted the video below showing a comet falling towards the Sun.

LASCO (Large Angle Spectrometric COronagraph) on board the SOHO spacecraft has seen very many comets since it started observing in 1996. SOHO has reported over 2000 comets, almost all of them found by members of the public. Thanks to the many amateur observers that hunt for comets in SOHO data, SOHO has seen many more comets than any other mission (there was another bright comet observed on May 10-11, 2011. A lot of these comets come from the Kreutz sungrazer family of comets. There is an active community of comet hunters, so if you think you’ve discovered one – and it is certainly possible that you may have – please check the latest reports over there. Thanks for sharing, galaxy387!

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