Neat. It’s a “armillary sphere”, also known as an “astrolabe”. Essentially it’s a theoretical model of the heavens, used since ancient times to assist in observations of the stars and perform calendrical calculations. The rings represent lines of celestial latitude and longitude with other aspects such as the ecliptic. Depending on age and culture they either have Earth at the centre (Ptolemaic) or are centred on the Sun (Copernican).
‘Working’ devices would be much larger and a small one like that would just have decorative use as a charm, pendant or whatever. In modern times, they’ve become popular with ‘new-agers’ and those with an interest in astrology (as opposed to astronomy) or things mystical, usually with addition of horoscope star signs and other symbols. You can buy them in various metals from the kinds of shops that sell joss-sticks, tarot cards, runestones and healing crystals.
When you say you hope it’s “authentic”, I’m not sure what that means. If you’re wondering whether it might be “ancient”, I’m perfectly certain it isn’t and, as I said, at that size it wouldn’t be functional for astronomical purposes. I would think probably made in the last 50 years or so.
en.wikipedia.org
