If you hold your finger out with your arm fully extended, it will cover sun or moon. This is even true for giant moons on the horizon. It’s always true; neither is very big (perceptually, from Earth).
The sun and moon are the same size in the sky. Their diameters both occupy one half of one degree of arc. Visual resolutions in the real world are measured in degrees of arc.
Specifically the sun’s diameter is 0.533 degrees and the moon’s is 0.52.
If you know your lens’s angle of view you can figure out the diameter of your sun or moon using the following equation:
(horizontal image res/angle-of-view)*0.5 = sun or moon diameter in pixels
The two easiest ways to find a lens’s angle of view are internet searches:
and camera tracking or other 3d software, which often has the data available.
With an HD image shot on a Zeiss Ultra Prime 40mm, the math looks like this:
(1920/34.7)*0.5=28 pixels.
Granted this is only to be technically correct. For various perceptual reasons, you and your clients will be unhappy with how tiny the sun or moon are. That’s your problem, not the camera’s. The eye’s ability to focus on one thing mimics a zoom lens while retaining a sense of your surroundings. Lenses cannot accomplish the same wide+telephoto feel, which is why there’s often magical thinking when it comes to moon scale. Utterly giant moons, looming apocalyptically over the horizon will be reduced to nothing more than dots when photographed.
case in point: that orange blob is among the biggest moons I’ve ever seen. Standing there in front of the Bank of America on Riverside in Toluca Lake, it was positively gigantic. You’ll have to trust me.
