Hipparchus was an ancient Greek astronomer who calculated the ecliptic and orbit of the Moon, and the paths of the sun and the moon, discovering in the process that the center of the universe was not Earth.

Hipparchus is a two-player trick-taking game in which players become ancient Greek astronomers and present their findings on the Sun, the Moon, and the Earth to one another. You want to share the study of one celestial body with your colleague without monopolizing it, yet still gain more authority than them.

In more detail, the game contains three suits of cards: Sun, Moon, and Earth, with ten copies of each. Each player gets a hand of fourteen cards and cannot rearrange them. The lead player plays 1-3 cards of a single suit, and when choosing something to play, you can't break up pairs or triplets in your hand. If you have three Earth cards in a row, you can play them only together as three Earths. The following player must play the same suit, if possible, but a different number of cards; if they can't do this, they can play 1-3 cards from either other suit.

If both players play the same suit, the player who played more cards wins the trick, stacks the cards in their collection, then leads to the next trick. If players play different suits, then the player who has fewer cards of their played suit in their collection wins the trick. (In a tie, the following player wins.)

When a player runs out of cards, the round ends. Each player tallies their score. If you have more cards in a suit than your opponent, you score points equal to the number of cards they have. Whoever has the highest score wins the round; the first player to win two rounds wins the game.