Question

why does the size of the object appear to be changed as it is observed from different countries distance​

Answer 1

Answer:

In the eye, image is always formed at retina which is at a fixed distance in eye.

So, when objects at different distances are seen by the eye, the image distance from the eye lens remains constant by changing radii of curative of the eye lens leading to change in focal length.

Answer 2

Answer:

Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances. To measure large distances, such as the distance of a planet or a star from Earth, astronomers use the principle of parallax.