Conjunction

In a conjunction, two celestial bodies share the same ecliptic longitude — seen from Earth, they stand in the same zodiac degree. Astronomically that doesn't mean they're actually close: a Venus-Jupiter conjunction is a perspective effect, the two are still separated by hundreds of millions of kilometers. They usually don't line up exactly either, because their orbits are tilted differently against the ecliptic.

In interpretation, the conjunction counts as a merging: the principles of the planets involved appear together and color one another. Whether that's experienced as pleasant or demanding depends on which bodies are involved — a Moon-Venus conjunction is traditionally read differently than a Mars-Saturn conjunction. Unlike the square or the trine, then, the conjunction is neither "harmonious" nor "tense" on its own.

A special case is a conjunction with the Sun: a planet standing very close to it becomes invisible in the sky ("combust," in traditional terminology). The familiar new moon is simply the conjunction of Sun and Moon.