Astronomy Magazine
Opposition and conjunction
The two alignments that decide when a planet is worth looking at and when it is unreachable.
A planet is at opposition when Earth passes between it and the Sun: closest, fully lit, and up all night — the best time to observe it. At conjunction it is on the far side of the Sun, lost in the glare, and for a spacecraft that means weeks of degraded or suspended contact while the signal passes near the corona. Mars oppositions come round every 26 months and Jupiter's every 13, and mission planners work to both calendars.
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Related terms
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Stealing a fraction of a planet's orbital momentum to go faster for free.
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The layer of broken rock and dust covering an airless world — and a serious engineering problem.
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Bringing a piece of somewhere else back to a laboratory on Earth.
Tidal locking
When a body's spin has been dragged into matching its orbit, so one face never turns away.
Questions
What is Opposition and conjunction?
The two alignments that decide when a planet is worth looking at and when it is unreachable.
Why does it matter?
At conjunction it is on the far side of the Sun, lost in the glare, and for a spacecraft that means weeks of degraded or suspended contact while the signal passes near the corona. Mars oppositions come round every 26 months and Jupiter's every 13, and mission planners work to both calendars.