--- In guide-user@y..., gblair@t... wrote:
>
> Richard Newman expressed concern over Albireo A's color changing
from orange to
> white when zooming from level 6 to 7 in Guide 7, as well as the B
component not
> appearing blue at any level.
It's not the level; it's the limiting magnitude. With a limiting
magnitude of 10.9, Guide shows colored stars. At 11.0, they're all
white. This is roughly the limiting magnitude of the Tycho-1
catalogue used in Guide 7. Fainter stars rarely have color indices or
spectral types available.
Albireo is shown colored at the brighter limiting magnitude. The
companion is a very pale blue (spectral type B9), so it might not be
noticed.
The 10.9/11.0 transition is also where Guide starts plotting GSC
stars. If you change the limiting magnitude from 10.9 to 11.0, you
may notice that a few of the additional stars that appear are not
magnitude 11.0, but 10.6, 10.9, etc. These are stars that are not in
the Tycho-1 catalogue.
With Guide 8, the Tycho-2 catalogue will be used. This has a limiting
magnitude of about 12.0, so Bill may change the transition point
accordingly.
Ross Shuart