The sun’s exact position is not always as easy to understand, as it may seem.

At first, the earth does NOT orbit around the sun, but “orbits” around the common barycenter Earth+Moon; this barycenter orbits around the sun.

The barycenter is always inside the rotating earth at the sublunar point; 1400 – 2000 km below the earth’s surface (depends on the moon’s distance). Hence, depending on the moon’s position, distances to the sun may be greater from the earth or from the barycenter.

Some not really useful, but maybe interesting data for this year 2019:

(Perihelion and Aphelion are the shortest and the longest distance to the sun in a given year)

Perihelion earth on January 3, 9h UTC at 147099770 km

Perihelion barycenter on January 3, 22h UTC

Aphelion earth on July 4, 18h UTC at 152104275 km

Aphelion barycenter on July 5, 13h UTC

Apparent angular diameter sun on Perihelion = 32’ 32”

Apparent angular diameter sun on Aphelion = 31’ 28”

This gives a difference of 64 arcseconds, or a mean daily variation of 0.35 arcseconds.

However, the variation is not linear… around aphelion, for 20 days, the diameters’s rounded arcsecond does not change, around perihelion the same is valid for 15 days.