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SOHO LASCO Comet Finders' Page

The form for reporting comets is at the bottom of this page.

Information needed to report a discovery of an object

We need to know the date, time, and position of the object for at least one image. We also need to know which telescope (e.g. C2, C3) it was observed in and the origin of your coordinate system (e.g. (0,0) in top-left corner). Use the format of past comet discoverers if you are unsure how to make a report.

The object should appear in at least 4 frames to be considered real.

Click here to use a web based tool to measure positions on real-time movies..


Common mistakes

There are a variety of common mistakes which inexperienced observers make. They report:

  • 1) stars, planets, or other known objects.
  • In every LASCO image you can observe objects whose trajectories are almost exactly horizontal. The majority of these objects are stars. (The rest being very occasional planets and asteroids.) Every C3 image has approximately 200-300 visible stars and every C2 image has approximately 10-30 stars visible. Stars will always move from left-to-right (due to SOHO's orbit about the Sun) at a speed of a few pixels/hour. Occasionally, planets appear in LASCO images and they, too, have a nearly horizontal motion. However, planets can move left or right through the field-of-view and can be faster or slower than the background stars. A list of expected planetary transits is provided at the 'C3 Transits' link. This link also provides dates of expected asteroid appearances in LASCO images. Overall, if you believe you have discovered a comet and its motion is nearly horizontal, chances are you've actually located a star, planet, or asteroid. Check the 'C3 Transits' link for known objects or use an ephemeris program to identify known stars, planets, asteroids,or comets. Click on the image below to see examples of stars and planets visible in a LASCO image.
    Note: The "rings" (or "wings") seen either side of the planets are not real. They appear because the planets frequently saturate the CCD, causing a bleeding of pixels along a single row.

  • 2) cosmic ray noise


  • Cosmic rays are very high energy particles which come from a variety of sources (e.g. solar flares, supernovae). They are of interest to lots of astronomers, but mostly just noise for us. We see lots of them in every image and occasionally, 3 or 4 of them hit the CCD in just the right places in consecutive images to fool us into believing there is a real object there. The cosmic rays can show up as points or as streaks. (http://helios.gsfc.nasa.gov/cosmic.html). Click on the image on the left to see typical examples of cosmic rays visible in LASCO images. (Note: ellipse = cosmic ray, circle = star.)



    A solar flare will heat and eject particles radially outward along open magnetic field lines (called solar energetic particles or solar cosmic rays). Every so often a large flare, positioned so that it is magnetically connected to SOHO, will produce a flood of cosmic rays that will completely blind our CCDs with noise. These somewhat rare events are called "proton storms" and can render our CCD observations useless for days. The lower image on the left shows a LASCO C2 image during a proton storm resulting from the "Bastille Day Event".

  • 3) debris streaks
  • Debris can refer to astronomical or human-made debris. The debris may be dust or spacecraft insulation which has flaked off. Visit http://lasco-www.nrl.navy.mil/debris.html for more detailed information. The image on the left provides a typical example of debris.

  • 4) objects already reported by someone else.
  • To see what others have reported, please see the recent reports page.
The mistakes listed above, although common among inexperienced observers, can be avoided. To avoid the above mistakes a new observer must be willing to spend time studying the typical speed, location, morphology, and brightness of comets that LASCO observes. In other words, study as many past comets as possible before you begin looking for new ones. Also, there are several resources at your disposal which can make the learning period less frustrating. A chat site for LASCO comet finders has been established at http://groups.yahoo.com/group/sohohunter/. Here one can ask questions and pick up tips from past LASCO discoverers who have years of experience. Also, Sebastian Hoenig, one of our experienced comet finders, has created a tutorial on 'How to Discover SOHO Comets' that is made specifically for new observers. The tutorial can be found at http://www.sungrazer.org. By studying past comets, avoiding the "common mistakes", and using the resources listed above the inexperienced observer will be able to discover LASCO comets much faster than those who search before acquiring the proper practice and knowledge.


Where should I look in the images to find comets?

A large percentage of LASCO comets belong to one of four known groups (Kreutz=85%, Meyer=6%, Marsden=2%, and Kracht=2%). A group's orbit is fixed in space with respect to the solar system but its location in LASCO images will oscillate annually due to SOHO's orbit about the Sun. Therefore, Mike Oates and Rainer Kracht have put together some web pages for the various groups showing the expected trajectory of the LASCO comets in the C2 telescope. Note how the trajectories vary throughout the year. Similar figures were published by Brian Marsden in his 1989 paper (Astronomical Journal, 98 (6), 2306-2321).
Kreutz trajectories
Other groups
It is recommended that beginning observers concentrate on the Kreutz group because they are far more abundant than the other groups. Also, Kreutz comets are typically easier to locate due to an apparently slower speed during peak observing months (geometric effect) and a more pronounced cometary appearance in LASCO C2 images. In contrast, the other groups' comets usually appear as condensed points that blend with background stars and cosmic rays. Overall, be extra skeptical when suspect comets do not appear along the predicted paths of the known comet groups.

This page has a (nearly...) complete set of images showing the tracks of the comets in the main groups throughout the year.



Use this form to report a new comet

Please fill out the appropriate fields below:
You must select your name from the name field. If your name is not in the list, please select "New User". You must click "Preview" before "Submit" to send your information.

You are strongly encouraged to read this page for instructions on filling out the below form, and also some rules and restrictions on reporting comets. You can also click on the blue "?" next to each field for help on what to put in the boxes.

Please choose your name from below. If this is your first time, choose "New User". A window will later appear, requesting you send an email to the sungrazer webmaster. Sending this email is entirely optional, however WE ARE UNABLE TO CREDIT YOU WITH A COMET DISCOVERY IF YOU DO NOT TELL US YOUR NAME! If "New User" window doesn't appear when you click "Preview", click here.

Has your name disappeared from the list? We periodically remove names from this page that have been inactive for a long time. (The list gets too messy, otherwise.) If your name used to be on the list but has since disappeared, use the "New User" option to submit your report and then send an email to sungrazer@nrl.navy.mil asking for your name to be re-listed.
Name:   


  

Time: e.g. hh:mm:ss, hhmmss, etc
(NOTE: 'Time' NOT NEEDED for "Potential Comet" posts)   
Date: e.g. yyyymmdd, yy/mm/dd, etc   

Camera and image size:   

Your (0,0) position:   

Comet group (if known):   

Frame time: X pos: Y Pos: (1st Position)   
Frame time: X pos: Y Pos: (2nd Position)
Frame time: X pos: Y Pos: (3rd Position)
Frame time: X pos: Y Pos: (4th Position)
Frame time: X pos: Y Pos: (5th Position)
Frame time: X pos: Y Pos: (6th Position)


When you press the "Preview" button, your report preview will appear below. Only then will the "Submit" button appear to allow you to submit your report.





To see what others have reported, please see the recent reports page. To view comet reports from previous months please visit the archive pages.

Something else to say?

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