This may be pure coincidence but while I was researching the Moonlights I came across the name Fairweather with a loose connection to the Moonlight family.
In the 1841 census for Inverbrothock (Arbroath) there is a family by the surname WYNTON living at Smithy Croft No. 15, including a daughter named ISOBEL aged 6. Also in the household is an Alexander FAIRWEATHER aged 10 (quite a common surname in those parts).
Now - George Moonlight's brother Alexander Moonlight (born around 1836) married an Isabella WYNTON in Arbroath in 1860. Could be that George, his brother Alexander, Isobel (or Isabella) Wynton and Alexander Fairweather all knew each other - maybe George just liked the name and added to his own later in life to make himself sound more exotic (as if Moonlight wasn't an unusual enough name in itself). Pure speculation, but you never know.
Sally G