Water, earth and air

[Stefan Wirtz_2]

[..] What is the purpose/meaning of the cloudband in that image?

This is the star constellation "Demon meridianus", the noonday demon. 
Mentioned first in a pre-christian hebrew bible, this seems to stem from ancient greek stories about Diana/Artemis or Pan. Generally a mediterranian warning to avoid noon's heat.
There is also a Czech and other slawic figure called the "Noon woman", which may be sourced from (byzantine) greek origins -- this one is explicitly dangerous for people who work harvesting on the fields during mid-day, killing them by heatstroke.
This version here regards such harvesters, interesting how such detail found it's way to a southwest-german book of mid 15th ct.
The Hausbuch text also mentions a lot of stars and "galaxia".

About the cloudband, good old Michael Scot had this image:



Cloudband and (here) starband seem to have the same function, representing a star band or galaxy.

This all has nothing to do with Voynich Ms, 
but it is interesting how non-christian, ancient and eastern themes left their mark.