Testing antenna aimed at cold sky vs hot ground – can this be conducted in daytime or must it be done at night?

QUESTION:
Testing antenna aimed at cold sky vs hot ground – can this be conducted in daytime or must it be done at night i.e. does sunshine or even sun behind cloudy skies ruin the sky or ground temperature difference?

ANSWER:
Daytime, Nighttime Sunny or Clouds, it does not matter.

The temperature of the Ground does change, and that can be factored into the equation, if you really want to do so. However, that is a small fraction of the number = just do it whenever it is convenient.