by Simen1 » Thu May 28, 2015 12:32 pm
I think its a too interesting thought to skip. Let me try four scenarios:
1.1 New Horizon is passing by a California Air Base at 10 000 km distance (same as New Horizons will pass Pluto) at a speed of 13,8 km/s. In comparison ISS is in a low earth orbit currently about 355 km altitude and 7,66 km/s speed. ISS is roughly 110 x 70 meters. New Horizons is considerably smaller with its roughly 2 x 2 meters, at a much larger distance, thus having an apparent magnitude far less then ISS. Roughly 2,4 million times (16 magnitudes) fainter. ISS have a maximum apparent magnitude of -4. New Horizons would be +12 magnitudes. The limit of the naked eye is about +6,5 magnitudes, making it invisible to the naked eye by a large margin. ISS is fast moving but not too fast for us to see. New Horizons would appear about 20 times slower do to the 35 times larger distance.
1.2 If New Horizons was passing closer, lets say at 100 km above sea level without disintegrating it would outspeed ISS by 6,4 times. No problem so far. But it would be about 150 times (6 magnitudes) fainter then ISS (ignoring friction glow). At magnitude +2 it would be visible to the naked eye assuming it would be fully sun lit when the sky is dark enough.
2.1 If you where standing at the night side of Pluto looking for a "full moon" New Horizons it would be far fainter then in scenario 1.1 due to Plutos large distance to the sun. At Plutos current distance of 32 AU it will receive about 1/1000 the light per area then it would around earth. Even with a large telescope it would be out of reach.
2.2 If it was passing closer to you standing on Pluto it would be brighter but sweep trough your field of view faster. If it was close enough to be visibly bright (+6,5 magnitude at 30 km) then it would sweep trough the field of view in a few seconds so you would probably not notice it. At 3 km and +1,5 magnitude (equaling the maximum brightness of Saturn) it would sweep through the field of view in a fraction of a second.
I have not double checked the calculations so please correct me if necessary.