Why doesn’t the Sun fill the sky on Mercury? I’ve seen a lot of photos showing Mercury in front of the Sun when it passes by and you can see just how tiny it is in comparison.

Here’s a great example:



So I’d expect if I was travelling towards Mercury in that photo that as the planet got bigger in my view so would the Sun and eventually I wouldn’t be able to see the edges of the sun because it’s so big at this distance... makes sense that an object gets bigger the closer you get to it!

However what confuses me is that if you were on the surface of Mercury... this is the view you’d get where it’s about a 6 times larger than when viewed from Earth.



So how is this so small when it’s taking the whole view up when we’re viewing it further away from mercury in the first photo? But we’re closer in the second photo but now the sun is smaller... How is the first photo possible (it’s an actual photo taken by NASA) why isn’t it taking up the whole sky in the second photo when you’re actually on the planet?
When looking at the first image, you need to take into account perspective distortion in images with a narrow field-of-view. This is the same effect that makes people look closer together than they actually are when photographed through zoom lenses (which is useful to bear in mind when reading the news these days!). Mercury is not as close to the Sun as the first image makes it appear.

You also need to bear in mind that objects in space tend to lack "depth cues": in the atmosphere, objects further away will become blurrier and more "washed out" due to scattering. In space, this does not apply.