This may seem a dumb question but I can't visualize this in my mind. If photons are travelling straight then from our eyes or a telescope we should only see part of the star, for example because our eyes or the opening of our telescopes aren't as big as the diameter of that star. If photons are not travelling in a straight line then we should see a blurry image not the actual shape of those objects. Can someone explain what is really happening?
The photons are not radiated only in perpendicular (normal) direction from the star surface. In fact, they are radiated into all available directions (180 degrees) from every point on a star surface. The same applies for galaxies as well. For this reason there are photons sent into all directions (including the Earth direction) from each point of a star / galaxy "surface". And so we can see every point of their surface.