Hi Pete,

MPCORB wouldn't be a factor here. That file provides elements for
asteroids, but nothing else. Comets are "sold separately" by MPC.

To update them, you would have to click on Extras... Asteroid/Comet
Options, and then on the "Add MPC Comets/Asteroids" button. Then
click on the "Click to download updated comet data and add it to Guide"
option.

If you've not done that for a while, you'll have somewhat outdated
orbital elements. I just went through the above procedure, and clicked
on 45P, and asked for 'more info', and.... %#$& it, it doesn't give you
the reference code provided by MPC. The orbital elements were published
on MPEC 2017-C71; Guide should tell you that. I should be able to fix
it, I think.

Since it doesn't show a reference at present, I'll instead tell you
that 'more info' should list the orbital elements shown below. If you
look at the elements Guide is showing you now, they'll presumably not
quite match. (Actually, those discrepancies of over a degree look
ugly; I'm wondering if at least one machine is sufficiently out of date
that it's using an orbit from a previous apparition, with a perihelion
sometime in 2011! But using the above update procedure should put you
right.)

-- Bill

P/Honda-Mrkos-Pajdusakova (45P) mag 5.6
Period of orbit 5.26 years (1921.9 days)
Perihelion distance 0.5325120 AU
Aphelion distance 5.52 AU
Orbital elements:
Semimajor axis 3.0251895 AU
Eccentricity 0.8239740
Inclination of orbit 4.2477000 degrees
Argument of perihelion 326.2860000 degrees
Long. ascending node 88.9770000 degrees
Date of perihelion JD 2457753.76530 (31 Dec 2016 6:22:01)

On 2017-02-21 18:35, pecorp@... [guide-user] wrote:
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> Looked for 45P last night and it wasn't there. Today a friend commented about its nearness to galaxies and recalled that my data put it on top of a bright galaxy. Turns out that with the same Dec 2015 version of Guide9 and the same full MPCORB.dat file, the Guide9 on the office computer has it at one location, and at a slightly different location on the observatory computer.
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> This afternoon I checked and all the basic Guide setup/location/time settings seem to be identical and the data file is copied from office to observatory. For 21:30 EST Feb 20 the observatory positioned 45P at 12 19 52.7 / 29 35 13 while the office positioned at 12 17 31.3 / 30 08 16. Then to confuse things further, while checking the observatory I pulled down a position of 12 14 46 / 30 46 22 using the EXTRAS/ASTEROID COMET OPTIONS/ADD MPC COMETS ASTEROIDS. The USE MPCORB box in this option is checked.
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> I'm mostly doing asteroid astrometry and occasionally (10% of the time?) when I try for a comet it's not there. This is probably what's happening. But exactly what is happening here? Suggestions solicited...
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> Pete Peterson I15
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