webspotting 8 - comet data

As published in the Feb/Mar 2009 issue of SCOPE, the newsletter of the RASC Toronto Centre. Republished here with permission.

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Need to know where a comet is? Trying to simulate an asteroid occultation? Fan of astronomy planetarium  software?

I regularly use Stellarium to simulate the night sky. It is a fun program to use, perhaps a bit of eye-candy, but free! I also use Cartes du Ciel. Not nearly as sexy but again free. Neither of these programs initially showed comets. Stellarium has some of the big asteroids on file. But for the new, lesser-known, and fast-moving bodies in our solar system, you may need to update your astronomy software. Any (all) modern astronomy programs will allow you to add or update asteroid and comet orbital elements. With the proper information supplied, the software will be able to place, move, and track the object fairly accurately, at least into the near future. The less that is known about the object, the more frequently you need to update.

In some cases, you will need to add newly discovered or recently updated orbital element information yourself. How you do this, the format you use, is very specific to your astronomy application. You'll need to consult its documentation or help files for details. Then when you're ready to tackle the updating of comet or asteroid orbital elements, where do you get this information? I use a couple of web sites.  

Actually, you might know one of these already. Eric Briggs regularly refers to Seiichi Yoshida's web site (http://aerith.net/). This person is a comet enthusiast! In the "Weekly Information about Bright Comets" section, you can pluck a comet for review. In the comet profile page, along with photos, the orbital elements are listed such as "q"(perihelion distance), longitude of the ascending node, and the orbit's eccentricity.

The resource I use for asteroid orbital elements is the amazing Solar System Dynamics site over at the Jet Propulsion Lab (http://ssd.jpl.nasa.gov/). The "Small-Body Browser" lets you search for objects by name or number. Once again, you'll be able to review the appropriate details like "a" (semi-major axis), "peri" (argument of perihelion), "M" (mean anomaly), and so on. Great orbital diagrams here too!

So? What are you waiting for? Get that Lulin data up to date!