Bill J Gray wrote:

>
> Hi Oliver,
>
> I am thinking about some sort of separation between "planets"
> and "natural satellites", but haven't quite decided how I'll go about
> this. I may also revise Guide so that planets are shown if they
> meet the magnitude limit criterion, _or_ if they would show a disk
> (more than one pixel) on-screen. Thus, the disk of the moon
> occulting the sun would always appear, and you'd evade the
> oddity of seeing the moon vanish near total eclipse

The lunar magnitude ought not to be a problem here: when the Moon
is really new (i.e. no sunlit part of the Moon is visible from Earth)
its magnitude is still as bright as magnitude -3, due to Earthshine.
And I don't think people set the magnitude limit brigher than -3 very
often.

> (and Mercury and Venus vanishing near transit).

The same applies to Venus: when at inferior conjunction, Venus too is
approximately as bright as magnitude -3. In this case most of the
brightness is due to sunlight being refracted in Venus' atmosphere.
Venus' brightness actually varies relatively little: when brightest
it is less than 2 magnitudes brighter than when faintest. Compare this
to e.g. Mars, where the span of magnitude variation is some 4.5
magnitudes.
Or to Mercury where the span of variation definitely exceeds 5
magnitudes.

> -- Bill

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