S4 LINEAR, and an Ion Tale

by Matt Tarlach


Last night - 7/27/2000 - I observed LINEAR from an excellent site at 8200' elevation in Lassen Nat'l Park in California. Instruments were 16x80 binos and an Orion Short Tube 80mm refractor.

Despite the excellent site (limiting magnitude 6.5+ at zenith, close to 6 near comet) LINEAR appeared to have faded since my last observation on 7/21, which was made from a good suburban site with limiting mags at least 0.5 lower. The coma was well concentrated but there was no bright nucleus as I had seen 6 days earlier. The tail was a broad fan-shape curving to the North, with an estimated length of only 0.5 degree. The southern edge of the tail appeared slightly more defined, suggesting an ion tail, but this was only perhaps 0.4 degree long and nothing like the long tail I had seen on the 21st.

I tried for the comet naked eye but without success. I think it was well below the threshold....it appeared dimmer in the telescopic view than some nearby stars, which were not visible naked eye, either. Sorry no better magnitude estimate but I don't have the skills to make an accurate one, and don't want to guess.

I have also gone over my notes again from the 21st and must confess a somewhat embarrassing error. I noted a feature that I later became confident was the ion tail, after viewing images posted on the web. In my field notes I recorded it as about one and a third eyepiece fields....and in writing up my report converted that into 4+ degrees (I was using a 20mm erfle with apparent field ~3.25d). With hindsight, and the benefit of seeing the comet again, I believe I probably judged the tail length of 1-1/3 fields with a 2.8x barlow in place....which would make the actual length more like 1.5 degrees. Sorry to all for an inexcusably sloppy bit of reporting.