A common misconception is that the Sun is larger when it is near the horizon than when it is high overhead. However, this optical illusion is not true, for the apparent size of the Sun is virtually the same when it is rising or setting near the horizon or when viewed overhead (in fact, it is very slightly smaller when viewed near the horizon due to refraction as well as the greater added distance in observing across the Earth's radius). This illusion has been wrongly attributed to landmarks near the horizon, such as homes and trees, supposedly giving a sense of perspective and whereas the same perspective is lost when looking at the overhead Sun bathed in an empty sky. As noted by Donald E. Simanek and Carl J. Wenning, the real reason behind this trick by our brain is the perception of the Sun (or Moon) being against a "close" or "distant" foreground and which is lucidly described by the above two references.

However, if we were approach the apparent size of the Sun methodically by studying it during perihelion and aphelion, we can detect a small change using photographic equipment thanks to the elliptical orbit of our planet around the Sun which leads to variations in distance (and apparent size) of the order of about 3.4%. More specifically, at perihelion each January, Earth is approximately 147.10 million km away from the Sun and whose apparent diameter is about 32.53' whereas, at aphelion each July, Earth is approximately 152.10 million km away and the Sun is characterized with an apparent diameter of about 31.46'. This difference of 5 million km between perihelion and aphelion leads to the slight change in the apparent diameter of the Sun as illustrated by the two images of the Sun below captured six months apart when the Sun was near its minimum possible perihelion (Jan 4/2023) and maximum possible aphelion (Jul 6/2023) and while crossing the local southern meridian.

Note: The change in the apparent diameter of the Moon is MUCH more dramatic between perigee and apogee and is fully documented elsewhere on this website (see here).