eyes-screen   On July 14th, 2015 the New Horizons spacecraft will fly by successfully flew past the dwarf planet Pluto and its 5 currently known moons. An important part of the mission is the educational outreach – involving the public. So in addition to a new module added to NASA’s Eyes on the Solar System software, called Eyes on Pluto, there is now an online program, Pluto Time, that helps explain how bright it would appear at mid-day on Pluto and how that would compare with Earth.

A Picture or the Inverse Square Law?
   At the Pluto Time web site you enter your location and then are told the next time it will be ‘Pluto bright’ at your location. This seems to be around your local time for dusk or dawn – before sunrise or after sunset. So this picture from Tucson Arizona, facing northwest toward the Catalina Mountains, is as bright as it would be on Pluto during the daytime. Or at least according to the web site.

A Picture or the Inverse Square Law?
On the other hand, the average distance from the Sun for Pluto is about 5,906,376,272 km (3,670,052,066 miles) compared with the Earth’s average distance of 149,668,992 km (93,000,000 miles). Within the confines of the solar system distances like this are often referred to as units of AU or Astronomical Unit. One AU is the Earth to Sun average distance, while Pluto is 39.5 AU. Using the Inverse Square Law we can also determine how much dimmer Pluto is than the Earth, or how much brighter Earth is than Pluto.
inverse square law   The Inverse Square Law measures how much radiation, light in this situation, will decrease as distance from the light source increases. To calculate one simply inverses the distance value (makes it a fraction with 1 as the numerator) and then squares this fraction. For example if the distance were twice as much or were to double (2) then you would write it as its inverse, 1/2, and when squared (1/2)2 you would have 1/4. This would mean that if the distance were to double or be twice as much then the amount of light would decrease by 1/4th. 3 times would equal 1/9th; 4 times would equal 1/16th, and so on.
   What would it be like on Pluto? As of this posting Pluto is approximately 33 AU from the Sun (4,936,729,732 km; 3,067,541,639 miles). So the inverse square of 33/1: (1/33)2 = 0.00092 means that Pluto receives nearly 1100 times less sunlight than the Earth, or that mid-day on Pluto is that many times dimmer than than mid-day on Earth. The Sun in the sky above Pluto may look like this simulated view from the surface of Pluto suggests.

Here’s How to Make NASA’s Pluto Flyby a ‘Teachable Moment‘ for Students:

Caution: Objects viewed with an optical aid are further than they appear.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

5 thoughts on “#PlutoTime

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