Re: Magnitude of Sun from Pluto?

I'm not sure what the distance from Pluto to the Sun will be when New
Horizons arrives, as Pluto's orbit is elliptical, but its mean radius is 40
astronomical units. At that distance, the Sun would be 8 magnitudes dimmer
than from Earth. (The calculation goes: take the base ten logarithm of the
distance from the Sun in astronomical units. Multiply by 5. Subtract 26.7.)

As the Sun is at magnitude -26.7 from Earth, that would put it at -18.7.
That's six magnitudes brighter (31X) than the full moon as seen from Earth.

In other terms: I didn't find a really good reference, but it appears that
full sunlight on the Earth illuminates at roughly 100,000 lux (lumens per
square meter), or about 10,000 lumens per square foot. At 40 AU, this would
be reduced to about 6 lumens per square foot. Indoor illumination is
supposed to be typically 30-50 lumens per square foot (200 for fine tasks),
so you might want to take a light source with you for comfortable reading
while you're orbiting Pluto.


Address scrambled. Replace nkbob with bobkn.

"PP" <none@xxxxxxxxxxx> wrote in message
news:4bd0t15ua0rr540aes4nbn78rtcis822lf@xxxxxxxxxx
> Sure was great to see that the New Horizons spacecraft had a
> successful launch and is now on the way to Pluto (9.5 years) and
> beyond to perhaps a Kuiper Belt object. Not too long ago such a
> mission to Pluto was thought to be unreasonable (25-30 year trip).
>
> In reading one of the news summaries it was mentioned that the Sun
> "appears like just a rather bright star" from Pluto. Wonder how
> bright? Perhaps like Venus -4? Anybody have a calculation of the
> relative magnitude of the Sun from the various planets?
>


.

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