that comparison should make you appreciate the unfathomable distances between even the most local astronomical objects, not underestimate it. The distance betw

that comparison should make you appreciate the unfathomable distances between even the most local astronomical objects, not underestimate it. The distance between continents is hard enough for the human brain to comprehend, and imagine the difficulty in trying to caputure an image with a telephoto lens of some resolvable feature in japan, from europe or america (forgetting the shape of the Earth's surface for a moment). Of course ever graceful, nature offers us a compromise. Most astronomical object (galaxies, nebula) are very big, and very very far away. It is not resolution that makes it difficult to see them (since they span an appreciable arc-width of our sky, e.g. search pictures of the angular width of andromeda galaxy or the orion nebula compared to the moon), but how faint they are. The photons they emit are travelling across swathes of the observable universe. They travel across scales where the presence of galaxy clusters warp the geometry of space-time, a turbulant voyage for these light rays. They travel across distances where space itself inflates like a balloon, the expanding universe sapping energy from them until they arrive in our detectors or eyeballs redshifted beyond recognision. This is why observatories and satellite-telescopes need to place a huge emphasis on scaling up mirror size to scoop up all the photons they possibly can, as opposed to strictly focusing on resolution - as an earthbound photographer might naively expect. Now consider the nature of planets, they are not diffuse clouds of molecules or dust lanes spanning galactic widths, they are tightly bound, tangible, physical objects. Now they might be our neighbours, trapped in the same spiral around the sun's gravitational well, but that doesn't mean they're "close" in any sense that the human mind could every really fathom. If we want to resolve atmospheric or geographic (is that even the right word for other planets?) features, we need to be able to achieve precise resolutions beyond what is normally required for other types of astronomical observation. Indeed, if you've every taken a class on optics or astronomy, you might be suprised how quickly fundamental limits of resolution that arise from lights wave-like behaviour - like airy disks - begin to veil that which we wish to observe, when playing around with frequiencies and aperture widths on a "humman" scale.