I'm a quite beginner to this stuff and maybe others would be able to say more but I'll start.
Angels are just angels. In medieval times people believed that stars and planets don't move itself but they are moved by angels.
There were angels responisble for planets or Zodiac signs. I believe there isn't any official list of them but you may check for
example this link from great Nick Pelling website:
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You have a cipher broken there, with plaintext containing sentences like
NOMEN ARIETIS SOLICET ANGELUS EIUS EST “SORON”
The name of angel governing of Aries is Soron
And in the middle ring you have star constellations. You can see Libra itself there. The guy holding a snake
seems to be Serpentarius/Opiuchus. Another guy may be Bootes and so on. Please notice that these
are neighbour constellanions to Libra.
Also notice little circles at constellations pictures. They are probably stars. For those people it was obvious which stars
the author had in mind. In the past stars were often described as body parts of their constellations. For example you could
said Caput Gorgonae (Gorgona Head) and everybody knew that you mean Algol star. There were much more such names like
Cauda Leoni (Leo tail) Cors Cancri (heart of Cancer) and so on.
So on the picture we have stars for each day of 23 September-23 October when Libra is "valid". And here my knowledge ends.
Is it describing some real astronomical phenomenon or is it just astrology and stars picked at random? If it's astrology then
these stars could suggest what you should do or not on these days because they could bring you good or bad luck.