I fucked up a little so I understand the confusion, stars are typically in capital letters, A, B, C.
though clear distinctions are also made here. B, C, D implies a hierarchy of orbits, A is the primary gravitational pull in its system
Aa, Ab, (etc.) is used when two (or more) stars have a common center of mass

Real implications of this example:
Kepler-16A and Kepler-16B have a planet that orbits both (but to be clear they do not having a common center of mass), so it is Kepler-16b, and I didn't look it up but I assume it's not 16ABb because there aren't any A or B planets to differentiate it with
Polaris Aa and Ab are orbiting around a common center of mass, and Polaris B orbits them from further away
Castor has 6 stars, here's an image
Aa and Ab are still the main center of mass in this system

as an added bonus, black holes do not have a naming convention yet, Sagittarius A* is just in the Sagittarius A region and * is to indicate an exciting or interesting object

and to my knowledge, it is theoretically possible for a planet to orbit an Aa star without orbiting an Ab star but I don't think we know of any, I assume it would be named like Aa b

[–] Eheran@lemmy.fmhy.ml 0 points 1 year ago (1 children)

When you say common center of mass, so you mean the as in something like... Once it is outside of the object? Otherwise I assume everything has a common center of mass with everything.

Thanks for the info!

[–] Clairvoidance@kbin.social 1 points 1 year ago

Common center of mass means they spin around each other, currently the moon orbits earth, but long long in the future, even though the moon is smaller, it will have waned the pull of the earth to an extent where you both go around in the same circle, this happens quicker with objects the more equal in size they are