If you can see stars at night, which are farther away than the sun, then you'd be able to see the sun with a telescope. You just would. But, we don't. Also, the sun doesn't get smaller and smaller and smaller until it just fades away into nothing. It stays the same relative size all day long, until sunset. You can literally watch it go down behind the horizon - and if you're extra lucky, you'll get to see the green flash (if over water). Perspective does not explain the green flash.