Given that they only happen about half as often, birthdays on Mars are a pretty big deal. Mars has its own calendar that is deeply important to the people who live there. Seasons are long and dramatic, and the passage of time is marked around them. Earth-based, traditional calendars, such as the Muslim lunar calendar, are kept there as well for their respective culture groups. Ramadan and Christmas happen at the same times everywhere in the universe. Even in places where they have nothing to do with what you see in the sky when you look up.

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Panel 1: Orson waves his hand dismissively. Orson: "It's okay. I can say that. No one in this club would turn me in."
Panel 2: Orson: "And whatever ends up on your sin sheet gets wiped clean when you turn seventeen anyways."
Panel 3: Orson: You've got to use whatever you can to fight the power, know'amean?" Maida: "Sure! That makes sense."
Panel 4: Orson: "How old are you, Maida?"
Panel 5: Maria, leaning into the conversation: "Actually, Maida's eightf birfday is a monf from now, innit Maida?" Orson, surprised: "Wot?"
Panel 6: Hansa, smiling: "Eight Mars years, Ah-bian. That's about fifteen Earth years. See, I knew she was Martian." Orson, unimpressed: "Right. Mars years."
Panel 7: Maida, concerned: "Okay seriously, though. What still gives it away? Do I still have a accent?"
Panel 8: Miss Odomo, from the front of the classroom: "...Maida, innit? Maria's mate?"