New Horizons Becomes Closest Spacecraft to Approach Pluto

The new 'dwarf planet' designation was a stroke of genius. It's not a planet but it ends in 'planet' so everyone is happy!

In elementary school, I charted out the average distance of each planet (yeah, in those days I called Pluto a planet) from the sun on common scale on an adding machine tape. Mercury, Venus, Earth, and Mars were all very close to the beginning end of the tape. The outer planets were far, far away, and the tape wrapped around several walls of my elementary school classroom. Yep, space is big.

And all the distances within the solar system are beggared by the distances between distinct stars in our galaxy, not to mention the distances among different galaxies. Arthur C. Clarke wrote an essay about these facts, titled "We'll Never Conquer Space."

http://en.wikiquote.org/wiki/Arthur_C._Clarke#We.27ll_Never_...

My understanding (which I got from an astronomer looking for moons) is that it'll be enough to get a clear look at major features on most (not all!) of Pluto's surface, but nothing spectacular. Realize that even today, we don't really know what Pluto looks like, so any knowledge is big knowledge.

Astronomers drove digital imaging sensitivity, so I reckon they’ve got it worked out. Skimming http://arxiv.org/pdf/0709.4281v1 , it looks like Ralph, the main visible-light camera, can distinguish between true blackness and a mere 3k photons per pixel, and at the margin can detect objects of magnitude 14. Coincidentally, that’s about the magnitude of Pluto from earth, and you can’t see it even with a small backyard telescope. So this instrument is less like a consumer camera and more like, say, night-vision goggles.

This paragraph originally did the math for Pluto’s brightness wrong (thanks to atakan_gurkan below for pointing that out), so instead let me refer you to a short but interesting Metafilter thread on exactly this question: http://ask.metafilter.com/23197/Darkness-at-the-edge-of-town .

One more factor – Pluto’s albedo is quite high. It reflects 0.5 to 0.66 of the light falling on it, as opposed to e.g. 0.14 for the moon (which is fairly dark in the scheme of things, but not at all hard to photograph; you can easily overexpose it in a grainless photo with a recent consumer DSLR).

So: dim, yes, but still clearly visible.