Conjunctions

As the moon moves around the earth and the planets move around the sun, we observe their movements against the background of stars. We often find it noteworthy when the moon and planets appear close to each other or to bright stars. These events 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 each type of conjunction anywhere from a few minutes to a few days apart. Their distances may be different for each. It's possible for them to have one kind of conjunction but not the other.

Another type of conjunction is in angular separation. That is 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. Those types of conjunctions 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.

To look up conjunctions of the sun and moon, please look up 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 sun is between one of those planets and the earth, the conjunction is said to be superior. When the planet is between the earth and sun, the conjunction is said to be inferior. 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 place on Earth. From such places on Earth, the planet will appear as a black dot crossing the face of the sun.

Only conjunctions of Mercury or Venus with the sun can be described as superior or inferior and only those two planets transit the sun. The other planets orbit farther from the sun than Earth, and so they never pass between the sun and Earth. Nor can they be seen to transit the sun from any place on Earth. There is a separate transits page with more information.

Use the table below to select conjunctions among solar system objects during the 2010-2029 period. The list will appear in the frame below it.