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NASA invites Earthlings to experience Pluto Time

David Dickinson, Correspondent
Jun 9, 2015, 16:26 UTC

Sen—The outer Solar System is a realm of freezing temperatures, a dark nether region where the distant Sun provides little warmth or light. Or at least, that is the perception that the public has of places such as Pluto and its retinue of moons.

But as New Horizons is set to make its historic flyby of the distant world next month on July 14, NASA is looking to bust that stereotype, and is inviting the public to experience high noon on Pluto for themselves. 

It is a basic law of physics: light dims to the inverse square of the distance. Move a candle twice as far away, and it will appear a quarter as bright. But at 33 Astronomical Units from the Sun (where one Astronomical Unit is the Earth-Sun distance of 150 million km, or 93 million miles) during the time of New Horizons’ encounter next month, the sunlight falling on Pluto will only appear 1/1089th as bright as a sunny day here on Earth.

Sounds dim, right? Well surprisingly, you could still read a book comfortably via sunlight on Pluto. The Sun shines at a dazzling magnitude -27 as seen from the Earth, and from Pluto, the Sun still sits around a very respectable magnitude -19. In contrast, a Full Moon as seen from the Earth shines at only a paltry magnitude -13, about 250 times fainter.

The process is simple: enter your location, and NASA will tell you when the ambient light level for that place falls to that equal to high noon on Pluto, assuming, of course, the skies are clear. Then simply make a Vine or post an image to Facebook, Instagram or Twitter with the hashtag #PlutoTime. 

Interestingly, “Pluto time” occurs on Earth right about when the Sun reaches two degrees elevation below the local horizon. This is still in the realm of civil twilight, which does not end at dusk until the Sun is six degrees below the horizon. Other markers include nautical twilight (12°), and astronomical twilight (18°).

Don’t forget to check out and document Pluto Time, coming to a sky near you.