That is a representation of the firmament above and the firmament below.
Being that this object dates back many hundreds of years, and is included in Catholic visions, art, publication, etc...Could you link a quote that describes it representing the firmament?
If you look at the history of it, its just the Catholic adaptation of an old pagan symbology
https://en.wikipedia.org/wiki/Globus_cruciger"Holding the world in one's hand, or more ominously, under one's foot, has been used as a symbol since
antiquity. To citizens of the Roman Empire, the plain round globe held by Jupiter represented the world, or the universe, as the dominion held by the emperor. A 2nd-century coin from the reign of
Emperor Hadrian shows the
Roman goddess Salus with her foot upon a
globus, and a 4th-century coin from the reign of
Emperor Constantine I shows him with a
globus in hand. The
orbis terrarum was central to the iconography of the
Tetrarchy, representing the Tetrarchs' restoration of security to the Roman world. Constantine I claimed to have had a vision of a cross above the sun, with the words "In this sign, you shall conquer" (Latin:
In hoc signo vinces), at the
Battle of Milvian Bridge in 312. His soldiers painted crosses upon their shields, and then defeated their foe,
Maxentius.
With the growth of
Christianity in the 5th century, the orb (in Latin scriptures
orbis terrarum, the 'world of the lands', hence the word "orb") was topped with a
cross (hence
globus cruciger), symbolising the Christian God's dominion over the world. The emperor held the world in his hand, to show that he ruled it on God's behalf. To non-Christians already familiar with the
pagan globe, the surmounting of a cross sent a message about the triumph of Christianity.
[citation needed] 
Topic: End of Story at least for Catholics (Read 33854 times)