Forgive the exaggeration. There’s actually no comparison between Jupiter and the moon. Jupiter is vastly bigger than the moon, although their distances are such that the moon appears quite large in our sky while Jupiter is only ever a bright point of light.
Nevertheless, we are in for a spectacular view on 21 September when Jupiter will be at Opposition. Opposition is the relative point in the orbits of Earth and Jupiter when the two planets are at their closest point, meaning that Jupiter will also be at it’s brightest. But no two oppositions are exactly the same, since planetary orbits are actually elliptical and not perfectly circular which means that the actual separation at opposition varies by as much as 75 million kilometres! Next week’s opposition will be a particularly close one, making Jupiter bigger and brighter in our skies than it’s been in a long time.
Even now, as it moves into position, it’s putting on quite a show. If you head out late at night, between 10pm and 2am, and look upwards, it will be immediately obvious as the brightest thing in the sky (after the Moon).
Unfortunately, unlike Mars, I can’t promise that it will look as big as a full moon, but it will be just under 50″ across – bigger than Mars was in 2003 when the infamous “Mars as big as the moon” hoax began.