[TML] The Sky at Night?

[Patrik Holmstrom]

On Dec 3, 2007 4:53 PM, Ewan Quibell <ewan at quibell.org.uk> wrote:
> Patrik Holmstrom wrote:
> > On Dec 3, 2007 2:50 PM, John Kwon <jtkwon at jtkgroup.com> wrote:
> >> On 12/3/07, Patrik Holmstrom <patrik.holmstrom at gmail.com> wrote:
> >>> On Dec 3, 2007 1:07 PM, Timothy Little <tim at little-possums.net> wrote:
> >>>> On Mon, Dec 03, 2007 at 11:18:44AM +0000, Ewan Quibell wrote:
>
> >>>>> Would the F7 V just look like a bright star or would it produce
> >>>>> something like moon light?
>
> >>>> It would illuminate about the same as a bright full moon, yes.  It
> >>>> would be a very dazzling star, apparent magnitude probably about -13.
> >>>> I don't think it would actually be dangerous to look at: despite the
> >>>> pointlike focus on the retina, the light passing through the pupil
> >>>> would be less than a microwatt.
>
> >>> That looks like it is in the ballpark. Assuming a luminosity of 2.1
> >>> sol I get an apparant magnitude of -14.5 or 6 times brighter than mean
> >>> full moon luminosity (-12.6).
>
> >> So we wouldn't need night vision devices, and we could read our comp-pads
> >> without using the backlight.
>
> snip
>
> > Also the frequency of those clear nights are another matter. Bitter?
> > Me? Got myself a new telescope a while back and the only clear night
> > in the last 4 weeks had hurricane strength wind gusts...
>
> But at 6x Moonlight on a clear night would you still get the equivalent
> of Moonlight on an overcast night?
>
> And what about the other way around? Say if the primary was the F7 V and
> the companion was the G2 V at 1000AU, what would the apparent luminosity be?

After checking why Tim got other numbers than than me I found a slight
error in my spreadsheet. For a F7V (lum=2.1) I get an apparant
magnitude of -12.6 and the G2V (lum=1) gets -11.7 which is full moon
resp. half that. The light during overcast conditions would of course
depend on exactly how thick the clouds are. I have found numbers from
3-15% but I have no idea how valid they are. Anyone?

/Patrik