They are visiting all the time. We do not possess the correct vision to see them entering and leaving.

We know there are so many different spectrums of light rays, and that our eyes are capable of only seeing a narrow band of this spectrum, the white light.

Infrared, or X ray and higher we are unable to see witout the aid of telescopes.


So we can take the word of the Vedas that they can make themselves visible when they want to, but generally remain unseen.