How do we have the equipment to picture and see cosmos and stars millions of light years away, but can’t just zoom-in to examine and view the surfaces of our interplanetary planets in the solar system?
In: Physics
Many objects that are extremely far away such as galaxies are also large enough (tens of thousands of light years across) that they would actually appear very large in our sky if they were brighter. For example M31: Andromeda Galaxy is over 2 Million Light Years away, but its apparent angular size in our sky is over 3 degrees. By comparison, a full moon is roughly half a degree across, meaning that the full major axis of Andromeda occupies 6 times as much space in our sky as a full moon. The only limiting factor that prevents us from seeing it with our eyes is its dimness, but this can be remedied with high aperture telescopes and cameras that are much more sensitive to light than our own eyes.
Now let’s think about planets. For a large portion of the year, Jupiter has the largest apparent size of any other planet in our sky, it varies between about 30-50 arcseconds. An arcsecond is 1/360 of a degree, much smaller than the moon or Andromeda, but not too small resolve a decent amount of surface detail by powerful telescopes with sufficient focal lengths. Pluto on the other hand varies in apparent size from 0.06-0.11 arcseconds, meaning that the limitation on seeing detail on Pluto is not dimness, but size.
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