by Chris Peterson » Sun Apr 18, 2010 10:50 pm
AdrianPB wrote:Last week’ s lovely Umbrella N GC4651 galaxy shown on APOD: is there a place in space where, if a human were viewing, presumably form a spaceship, they would see what is seen in this image , or is this image in part determined by the optics etc of telescopes and their capacity to capture light with efficiencies way beyond the capabilities of the naked eye?
We would never see anything at all like this. There is certainly a place in space between here and NGC4651 where the galaxy would have the same size to your naked eye as it appears to have in the image on your monitor, but it would just be a gray, nebulous cloud. In brightness it would look the same as the Milky Way, and if you were decently dark adapted, you might see some faint structure- just as you can in the Milky Way.
The limitation is your eye. Extended objects don't change in surface brightness as you get closer. The total amount of light increases, but so does the size, and so the brightness per unit area is unchanged. And for virtually all non-stellar deep sky objects, that brightness is too little to trigger your cones, which provide high resolution color vision. As humans, we live in a gray universe.
[quote="AdrianPB"]Last week’ s lovely Umbrella N GC4651 galaxy shown on APOD: is there a place in space where, if a human were viewing, presumably form a spaceship, they would see what is seen in this image , or is this image in part determined by the optics etc of telescopes and their capacity to capture light with efficiencies way beyond the capabilities of the naked eye?[/quote]
We would never see anything at all like this. There is certainly a place in space between here and NGC4651 where the galaxy would have the same size to your naked eye as it appears to have in the image on your monitor, but it would just be a gray, nebulous cloud. In brightness it would look the same as the Milky Way, and if you were decently dark adapted, you might see some faint structure- just as you can in the Milky Way.
The limitation is your eye. Extended objects don't change in surface brightness as you get closer. The total amount of light increases, but so does the size, and so the brightness per unit area is unchanged. And for virtually all non-stellar deep sky objects, that brightness is too little to trigger your cones, which provide high resolution color vision. As humans, we live in a gray universe.