Image 1 Caption: A 16th century engraving of Ptolemy (c.100--c.170 CE) being guided in his observations by Urania (AKA Astronomia), muse of astronomy---astronomy is the only science with a muse.
Ptolemy is wearing a crown because the Middle Ages and Renaissance tended assimilate him to the Ptolemaic dynasty that ruled Hellenistic Eygpt---Cleopatra (69--30 BCE) was the last monarch (a queen regnant) of that dynasty.
Ptolemy may be observing the
fixed stars----which
Isaac Newton (1643--1727)
hypothesized as defining the
reference frame
of absolute space---of course,
he was wrong about there being
absolute space---but it was
just a theory.
Explication of the term fixed stars:
Yours truly usually means
the traditional
fixed stars
when yours truly says
fixed stars.
For a fullish explication of
inertial frames,
see file
frame_reference_inertial_frame_basics.html.
The Fixed Stars:
Images:
Local file: local link: ptolemy_muse.html.
Image link: Wikipedia:
File:Ptolemy urania.jpg.
Image link: Wikipedia:
File:Observable Universe with Measurements 01.png.
File: Ptolemy file:
ptolemy_muse.html.