[BAA Comets] COMET MAGNITUDES and the MPC

[Richard Miles]

Finally, starting in 4 day's time, I see that the MPC are switching to a 
sensible system for expressing comet magnitudes as per the appended note.

Looks like we will need to put together a note to explain this new approach 
for the benefit of observers.

Richard Miles
BAA

----- Original Message ----- 
From: <mpec at mpcdb1.cfa.harvard.edu>
To: <rmiles at baa.u-net.com>
Sent: Friday, April 20, 2018 4:55 PM
Subject: MPEC H54: COMET MAGNITUDES AND A/ OBJECTS


> M.P.E.C. 2018-H54                                Issued 2018 Apr. 20, 
> 16:47 UT
>
>     The Minor Planet Electronic Circulars contain information on unusual
>         minor planets and routine data on comets.  They are published
>    on behalf of Division F of the International Astronomical Union by the
>          Minor Planet Center, Smithsonian Astrophysical Observatory,
>                          Cambridge, MA 02138, U.S.A.
>
>             Prepared using the Tamkin Foundation Computer Network
>
>                              MPC at CFA.HARVARD.EDU
>            URL https://www.minorplanetcenter.net/    ISSN 1523-6714
>
>
>                       COMET MAGNITUDES AND A/ OBJECTS
>
>
> 1. Comet Magnitudes
>
>     Comet observations were first published routinely by the Minor Planet
> Center (MPC) after the move from Cincinnati to Cambridge in 1978.  The
> Editorial Notice on Minor Planet Circular 4391 [1978 Mar. 1] remarks 
> (noting
> that the original all-capitals text has been changed to mixed-case):
>
>    "We intend to continue to issue the M[inor]P[lanet]C[ircular]s in
> essentially the same form as before.  The principal change being that some 
> of
> the less urgent cometary data, hitherto published on the IAU Circulars,
> will be transferred here."
>
> and, in referring to the lists of observations published in these
> Circulars:
>
>    "In the case of comets, the notations T and N stand for the total (m_1)
> and nuclear (m_2) magnitudes, respectively."
>
>     Since 1978 the MPC has made the use of T and N mandatory for magnitude
> estimates of comets.
>
>     In the new ADES format, the notations T and N are not supported. 
> Rather,
> a comet's magnitude is there expressed as a value in a given photometric-
> aperture in a given band.
>
>     The MPC intends to end its enforcement of the use of T and N on comet
> magnitudes effective Apr. 24.
>
>     Starting on the above date, observers should report comet magnitudes 
> in
> the same form that they report minor-planet magnitudes.  See MPEC 2018-H21
> for examples.
>
>     Observers who wish to continue using T and N may do so, for as long as
> they report their observations in the 80-column format.
>
>
> 2. A/ Objects
>
>     The MPC is clarifying the circumstances under which an A/ designation
> is assigned.  The original implementation of the current cometary 
> designation
> system (see Editorial Notice on MPC 23803-23804 [1994 Aug. 28]) describes 
> A/
> designations as:
>
>    "If necessary, the prefix A/ would precede a comet designation that
> actually refers to a minor planet (or asteroid)"
>
> It is not a requirement that an object has been designated previously as a
> comet for an A/ designation to be assigned.
>
>     An A/ designation will be used for an object with an osculating
> hyperbolic orbit that has not been reported as cometary.
>
> Gareth V. Williams           (C) Copyright 2018 MPC           M.P.E.C. 
> 2018-H54