What Are Superior and Inferior Solar Conjunctions?
When a body aligns with Earth on the far side of the Sun, it forms a superior conjunction. When it lies between the two, it forms an inferior conjunction.
Venus, at the upper right of the solar disk, was positioned exactly between the Sun and Earth during an inferior conjunction in 2012.
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In the constant movement of space, astronomical objects can come into an alignment where they are at solar conjunction—forming a relatively straight line with Earth and the Sun
From our planet’s view, when that object is on the opposite side of the Sun, the formation is a superior conjunction. When the celestial object is positioned between the Earth and Sun, it is an inferior conjunction.
A Rare View
Since the Sun is so large and bright, we can’t see a planet in superior conjunction from Earth. But if the conditions are right, and we have the right equipment, we can observe some inferior conjunctions.
What’s visible in your night sky now?
The outline of the Moon is easy to see at inferior conjunction when it creates a solar eclipse—as long as you have the right safety equipment to protect your eyes.
(Of course, never look directly at the Sun without proper protective equipment.)
How often do solar eclipses occur?
The orbits of the two inferior planets, Mercury and Venus, take those worlds into superior conjunction as they pass the opposite side of the Sun, and then into inferior conjunction as they pass between the Sun’s disk and Earth.
Meanwhile, the five superior planets—Mars, Jupiter, Saturn, Uranus, and Neptune—have orbits that create only superior conjunctions.
Conjunctions can create communication problems for rovers. (This image is an illustration using data from NASA.)
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Radio Interference
Conjunctions of either type can be a headache for space explorers. NASA reports that its Mars orbiters and rovers have to go dark when the red planet is in a superior conjunction position with Earth and the Sun.
In that alignment, the powerful electromagnetic fields of our star scramble the instructions sent to the craft from central command, potentially resulting in disaster if the rovers were to follow these partial or distorted instructions.