Conditions for planets and the Moon

Seeing is everything. Darkness and moonlight barely matter, and a hazy, humid night that ruins deep-sky work is often the steadiest night of the year for planetary detail.

Planets are small and bright. You are working at high magnification where atmospheric turbulence sets the limit, not sky darkness. Jupiter does not care that the sun is only 8° below the horizon, and it does not care that the moon is full.

What it cares about is steady air. Look for stagnant, settled conditions — a high-pressure ridge, light winds aloft, no recent frontal passage. Observing a target high in the sky helps a great deal, because you are looking through less atmosphere; the difference between a planet at 20° and the same planet at 60° altitude is dramatic.

Modern planetary imaging exploits this directly, and the technique has a name: lucky imaging. You record thousands of very short exposures — short enough that the atmosphere barely changes during each one, typically 100 milliseconds or less and often only a few milliseconds for bright planets — then keep roughly the sharpest ten per cent and align and stack those. In effect you are waiting for the brief moments when the turbulence happens to sit still, which is why a stacked result can far exceed what the same night shows visually.

In the window finder, the planetary mode weights seeing heavily, ignores moonlight entirely and applies only a light darkness penalty. It will regularly hand you a window an hour or more before the deep-sky mode opens.