Conjunctions

As the moon moves around the earth and the planets move around the sun, we often find it noteworthy when two objects appear close to each other. These objects are called conjunctions.

A conjunction in right ascension occurs when one object passes another and is due north or due south of it. Both objects will be on the same line of right ascension and at right angles to the celestial equator at that moment.

A conjunction in celestial longitude occurs when on object passes another and both are on the same line of celestial longitude. Both will be at right angles to the ecliptic at that moment. Since the ecliptic is at an angle to the celestial equator, two objects can go through a conjunction in right ascension and a conjunction in celestial longitude anywhere from a few minutes to days apart. Their distances may be different for each. It's also possible for them to have one kind of conjunction but not the other as one or both objects change direction just after one conjunction but before the other can occur.

Another type of conjunction is in angular separation. This proper term for this is appulse. It's simply the measure of how far apart they are without regard to whether they are on the same line of right ascension or celestial longitude. Appulses among solar system objects are listed below. If you're interested in the other types, please explore the information in the event finder database which also contains conjunctions with bright stars.

Conjunctions of the sun and moon aren't included here, because those are in the moon phases and eclipses pages.

When you look up conjunctions of the sun and Venus or the sun and Mercury, you may be interested to note whether a particular conjunction is superior or inferior. When the planet is on the same side of the sun as Earth, the conjunction is said to be inferior. When the planet's on the other side of the sun, the conjunction is superior. Sometimes, at inferior conjunction, the planet will transit the sun. That means it will pass in a line of sight between the sun and some region on Earth. The planet appears as a black dot crossing the face of the sun. Please visit the transits page for those events.

Use the table below to select conjunctions among solar system objects during the 2020-2039 period. The list will appear in the frame below it.

In a few cases, an appulse may be omitted because two objects didn't drift very far from each other before they began getting closer again. In these lists, if multiple appulses occur before the objects are ten or more degrees from each other, only the closest will be listed. This prevents the list from becoming unwieldy as minute variations in object positions bring them slightly closer again--sometimes several times per day--while the objects are generally separating.