reply to post by cheesy
I see that this thread has been assigned as a hoax.
Because it IS a hoax. Here's the ephemeris I generated over a month ago for my usual observing site, using just the astrometric data up to, but not
including, September or later:
Now I wasn't at my usual observing site when I was at Chiefland this weekend, but it's still the same state so topocentric parallax will be too
small to matter at this distance.
I took this quick image of ISON on Sunday morning from about 09:06~09:17 universal time.
It's just a quick shot taken so that I could prove its location later, so the center of the streak formed by the nucleus corresponds to its position
at about 9:12 UT. That's November 3.383 in fractional day format, right between these two entries in my ephemeris which I generated over a month ago
at half hour intervals, using just the data up to September, but not including any data from September or later:
2013 11 03.374290 11 25 00.507 +04 42 49.91
2013 11 03.395123 11 25 07.483 +04 41 54.74
The coordinates of ISON should therefore be between those two sets of coordinates, and indeed they are. I cropped the above image with ISON centered
in the image, so the coordinates of the center of the image therefore correspond to ISON's coordinates. As you can see at the above link, the
coordinates determined by astrometry are:
Center (RA, hms): 11h 25m 03.719s
Center (Dec, dms): +04° 42' 35.824"
Right between the two sets of coordinates above, ISON is on-course and that course has not changed.
However, what the thread was about, the changing of the comet's orbit was not a pure invention by the OP in that regard. Historically, comets have
not behaved as they have been expected given multiple early determinations of their motions as they approach the sun.
As I mentioned, the term "non-gravitational effects" is repeatedly used in historical accounts of the motions of the most prominent comets but with
little basis in genuine, specific fact. Of course, the average internet user today does not have access to those accounts from the old books.
Yes, they do. It's called a "library." There's not some grand conspiracy to keep this information from the "average internet user." The
internet does not entirely replace the function of a library, particularly a university library. You can visit public university libraries for free
and do all the research you want there. You may need a membership to check books out, but you don't need it for simply doing research and making
scans and photocopies in the library itself. Non-gravitational forces of comets due to outgassing do have basis in "genuine, specific fact," but
are minor, especially in the case of a long period comet like ISON. Non-gravitational effects are minor, especially over short time scales. They are
very important in determining the long-term orbits of periodic comets that constantly orbit within the solar system and are observed over hundreds of
years, but they are less important to long-period comets where the effects weren't even detected until the late 1960's and 70's with high precision
astrometry. Even then, because of how short the period is when the comet will actually be observable, the non-gravitational effects of outgassing are
of academic interest more than anything else; they can make the difference in the long-term evolution of the comet's orbit and determine whether it
will ultimately be a hyperbolic comet or not.
"Modern astrometric positions, particularly those that are referenced to Hipparcos-based star catalogs and where the brightest pixel is employed as
the true position of the cometary nucleus, are usually accurate to the subarcsecond level."
In other words, more than accurate enough even for most telescopic astrometry.
"Yet multiple apparition orbital solutions for active short-period comets cannot often provide a root mean square (rms) residual (observed
minus computed observational position) that is subarcsecond."
In other words, where it matters is with short-period comets for which astrometry and ephemeris must cover multiple orbits of the comet, not long
period comets like ISON.
All the modern "researcher" can find is explanations from modern conventional science that protects itself by ignoring what is really happen with
Modern science does no such thing.
Nor are you limited to "explanations from modern science," you can look back at the old books on the subject quite easily by visiting this
mysterious "library" thing.