The aim of this service is to provide charts (using Guide 9.0) and suitable comparison stars
for relatively bright comets,
i.e. brighter than magnitude 10-11, to aid observers in making brightness estimates.
To avoid confusion with Flamsteed numbers we have underlined the magnitudes of all comparison stars.
Stars with B-V<1.0 were selected where possible; those with B-V>1.0 are given in italics, and should only
be used when no suitable alternatives are available.
The source of the comparison stars on these standard charts is primarily the Tycho-2 catalog, of which only VT-magnitudes
are used. When reporting data to the ICQ (International Comet Quarterly) the source code thus should be given as TK,
unless indicated otherwise.
We plan to issue new charts on a regular basis, if possible not later than 2 days before the date of first observation.
Occasionally we also issue special charts for fainter comets that are of particular interest.
Below magnitude 10-11 comparison stars usually are taken from a different source (such as APASS with ICQ code AQ,
ASAS-3 with ICQ code AU and TASS4 with ICQ code TA), because Tycho-2 is becoming very unreliable here.
It should be noted also that the ICQ advises against the use of Tycho-2 for comets fainter than magnitude 10.5.
So be sure to always check the proper code(s) given on the top right corner of the chart.
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Currently we have charts available for:
Chart 1 C/2017 O1 period 10 August - 18 August 2017
Chart 2 C/2017 O1 period 23 August - 30 August 2017
Chart 3 C/2017 O1 period 30 August - 5 September 2017