SOHO LASCO Comet Finders' 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..
The form for reporting comets is at the bottom of this page.
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" seen around 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 below 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. For an example of a proton storm, click on the image below for a C2 movie of 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 here http://lasco-www.nrl.navy.mil/debris.html for more detailed information. The image below 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.
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).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.
Current tracks of SOHO-observed comet groups in LASCO C3 and C2
The area indicated on the below images (click for a larger image) shows where the comets from the four major SOHO-observed groups are currently being seen in the LASCO images. This area will change from month-to-month. The images will be updated appropriately.Note: These images are designed to give an approximate idea of where to look for SOHO comets in any given month. Some group members may fall slightly outside the indicated area(s). Also, Marsden, Meyer and Kracht comets are occasionally seen in C3, but very rarely, hence their exclusion from the below images. Non-group comets can, and do, appear almost anywhere in the C2 and (less often) C3 images. Non-group comets are very rare, however. Newcomers to comet hunting are very strongly encouraged to stick to hunting for Kreutz-group comets until they are fully experienced.
| C2 Kreutz-group | C3 Kreutz-group | C2 Marsden-group | C2 Meyer-group | C2 Kracht-group | ||||
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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.
To see what others have reported, please see the recent reports page. To view comet reports from previous months please visit the archive pages.
