The Occultation Of Star PPM200723 On The Night Of October Fourth And Fifth(1996)


On 30 September of this year, Brian Skiff (bas@lowell.edu) of the Lowell Observatory posted the following message on the newsgroup sci.astro.amateur:

"Comet observers and others may want to remember the possible occultation of a mag 9 star by Hale Bopp on Friday evening 4/5 October 1996. ...along a path from SW-NE somewhere across the western US.

This event is of interest for permitting a direct determination of the size of the comet's nucleus. We infer indirectly from things like the total brightness and gas & dust production rates that this comet is huge by comparison to others we know about---but just how big we'd like to know.

Current information and updates will be posted in Marc Buie's area of the Lowell Observatory Web site... This page includes the current ground track (as a map and tables), CCD frames of the field ground the appulse/occultation star, and other information.

Therefore the occulation would have provided a good estimate of the nuclear size of the comet-at least one way to tell the size of Hale Bopp. And as this posting promises, amateurs and others would be informed regularly of any changes in the prediction or updates. The prediction was posted to the site on September sixteenth. So in this statement we have two concerns;first-the ability to estimate the size of the nucleus and second-the updating of information. (A comment below on these two points).

Then there's this quote from the Sky And Telescope Bulletin of 9/6/96:

Lawrence Wasserman of Lowell Observatory reports that, "On October 5th, Comet Hale-Bopp will occult a 9th-magnitude star. The event will be visible from the western United States, and we'll provide updates as the date nears. Conceivably the nucleus itself, believed to be only 20 to 50 kilometers wide, may briefly block the star's light."

Initial Map

This was the map of the estimate, of local occultation placed on the web site below, on 9/16/96. It was titled, "last updated 1996 Sept 16"! Of course this was the first and only data before the occultation.

Final Map (posted after the occultation)

This map was the promised update prediction. Only it didn't get posted prior to the occultation. It was posted a week after.

And the size estimate...There were some lame excuses, such as, the weather was bad for all of our teams but one in Snowville, Utah. An examination of weather reports for the night of October fourth to the fifth, revealed skies clear-no overcast. And the one team that claimed to have clear viewing? There has been no clear evidence presented from this observation. The only results presented on the site are vague and ambiguous. Even after several emails to Mr. Wasserman, most responded to with silence, explanation was,

"So far, we have (unfortunately) no results. The track moved to the north (probably crossing Oregon) and the observers we sent up there were mostly clouded out."

Larry Wasserman

As I thought more about this, I realized that NASA must have another way to image the apparent size of the nucleus. We have radar from the Magellan Project that penetrated the covering of Venus to map its terrain. Surely they could use this same technology to at least make some reasonable estimate of Hale Bopp's heart. There were also images of Hyakutake's inner coma by the same technology. I was able to communicate to an acquaintance from a well known university, although I felt he was quite cautious with the words that he used. This Professor was willing to share with me the limited information, that Hale Bopp has not been imaged due to the inability of radar to penetrate its inner coma. To my knowledge the only thing that can stop or block radar, is either the technology used in stealth aircraft or a very strong EM field.

The so-called results of the occultation can be found at this site:

http://www.lowell.edu/users/buie/occ/hbresults.html
(May no longer be available)

  Are we in danger? Is there something that we could be doing to prepare, if we were only told? 
 
copyright 1996 gary d. goodwin