[BAA Comets] NEW - Interactive comet finder charts

[Graham Relf]

In response to requirements elucidated at the Comet Section meeting on 
18th May, the comet ( http://britastro.org/computing/charts_comet.html ) 
and asteroid ( http://britastro.org/computing/charts_asteroid.html ) 
finder charts on britastro.org/computing will have a new feature from 
now on. A preliminary sample can be seen at 
http://britastro.org/computing/ch/_63PTest.html (63P/Wild).

As you move the mouse over the chart certain data for the nearest star 
are displayed below it:

Star id (Flamsteed/Bayer or H... Hipparcos or T... Tycho)
V magnitude (+ "variable" if the star is variable in the Hipparcos/Tycho 
data)
B - V (colour index; just a few stars do not have the data for this)

The id is given so that further information can be found elsewhere if 
desired.
V magnitude is given to enable visual comet magnitude estimation using 
the defocussing technique (see J.Shanklin, BAA Observing Guide to 
Comets, 2002).
B - V is given so that stars with a similar colour index to the Sun can 
be used. Dust comets are reflecting sunlight so comparison magnitudes 
need to be for similar stars. The Sun's B - V value is reckoned to be 
0.66 (see 
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1992PASP..104.1035G&db_key=AST&data_type=HTML&format=&high=44b52c369023103 
David F. Gray, The inferred colour index of the Sun, 1992).

The chart also displays green boxes around the most Sun-like stars: 
those in the range 0.60 < B - V < 0.72.

The interaction is done using standard HTML/JavaScript techniques that 
have been around for many years and so should work in all browsers. It 
has been tested in FireFox 20 and Internet Explorer 10. The code is 
generated automatically by our own chart generator using Hipparcos/Tycho 
data. Once you have the chart in your browser no further internet 
connection is need for the interaction.

If you print the chart you will not get the star data. The idea is that 
you select the stars you want and make a separate note of their 
characteristics, perhaps written on the print. However, if you save the 
whole page from your browser you should be able to view it from disc 
with the full interaction.

The interactivity is not yet in the red-on-black versions of the charts 
but that will come soon.

Please tell us about any problems or modifications you think would be 
useful. I have already had feedback that the star data do not follow the 
mouse in early versions of FireFox. It would be useful to know about 
other exceptions, though I am not sure at this stage what could be done.

I hope I have demonstrated with this that having our own chart generator 
is an advantage because we can make it do what we really need. (And I 
enjoy the challenges involved.)

Graham