Birthdays

People born on the same day of the year in Astrocracy belong to the same template. The local name for people with the same birthday is "geminis". 

Odd months mean that you are vaguely more inclined to flashy displays than diligence. People born on even-numbered days tend to be pretty normal and unambitious, and one even day is pretty similar to another. Odd-numbered days are less regular, every other odd-numbered day is less regular than that, etc. Solquinoxes (that is, people born on an equinox or solstice) tend to be the weirdest of all. 

New Year's/fall equinox (Unuary 1)

Kind of evil, on purpose. A bunch of them run a country. A very specific sort of trustworthy: good at coordinating with each other, including in abiding by internal rules which keep them from collectively getting banned from normal society, and are known to keep their word, though they can at times be slippery about exact phrasings.

• Ian's twin, Nicolas

Winter solstice (Triinary 1)

A reputation for mad science, both inventing things and causing catastrophes.

Spring equinox (Quintamber 1)

Reputation for being good. Responsible for a lot of social change for the better. They're known to be very charismatic, eloquent speakers, and are frequently martyred as part of their activism. Particularly tyrannical rulers throughout history have been known to preemptively order babies born on that day put to death.

• Jesus

Summer solstice (September 1)

Template: Jida. Inclined to do immoral-seeming things for the greater good, which then go wrong and the greater good does not materialize. Disproportionately likely to commit suicide. Tend to care about the poor and donate to charity. Sing pretty well but aren't really inclined to make a career of it. Names almost all have Js and Ds in them. Statistically more likely to have dark curly hair.

Characters:

• Jackie
• Jordan
• Judas

September generally

Inclined to politics and achieving goals socially rather than scientifically

New Year's Eve (October 32)

An even day. Template: Alphabet Soup

In-universe book says:

Affinities: Enjoys sculpture and cleaning, good with animals, trusting, very sincerely focused on doing right by the people in front of them.
Enmities: Anxious, flakey, and socially prone to overthinking; alternatively, bravado-filled and underthinking-prone. Either way, impulsive.
Oddities: Their names tend to break down into pronounceable letters! Ex. Ariel (REL), Casey (KC), Ciel (CL).

Characters:

• Ian
• Ivy Gilbert (pet store)