Oppositions
When Earth passes between the Sun and an outer planet.
What Opposition Means
Opposition occurs when Earth is directly between the Sun and an outer planet — the planet is at the point in its orbit directly opposite the Sun from Earth's perspective. At this moment the planet rises as the Sun sets, reaches its highest point at midnight, and sets as the Sun rises. It is visible all night.
Opposition is also the moment of closest approach — the planet is at its minimum distance from Earth and therefore at its maximum brightness. For Mars, this can make it dramatically brighter than Jupiter. For Jupiter, it's the best the four Galilean moons will ever look from Earth.
Every opposition is worth noting. But not all oppositions are equal — the orbits of Mars and Earth are both elliptical, meaning some Mars oppositions are far more favorable than others. A perihelic opposition (when Mars is near its closest point to the Sun) can make Mars appear twice as large as an aphelic opposition.
The Outer Planets
Every ~26 months
Can outshine Jupiter at closest approach
Rises at sunset. Visible all night. Red and unmistakable.
Mars varies dramatically in distance — at its best opposition it's 6x closer than at its worst. Opposition year matters.
Every 13 months
Brightest planet for most of the year
Rises at sunset. The four Galilean moons visible through binoculars.
Jupiter's moons change position night to night — track them over a week and you're watching the same geometry that convinced Galileo the Earth wasn't the center of everything.
Every 12.4 months
Steady golden light — unmistakable once you know it
Rings visible through any small telescope. Tilt of rings changes year to year.
The rings are currently tilting toward edge-on. By the late 2020s they'll be nearly invisible before opening again.
Every 369 days
Barely naked-eye on dark nights
Appears as a blue-green disk in binoculars. No obvious features.
Uranus rotates on its side — its poles face the Sun and Earth. The seasons on Uranus last 21 years each.
Every 367 days
Never visible to the naked eye
Requires a telescope. Blue disk, no surface detail visible.
Neptune was discovered in 1846 by predicting its position from gravitational perturbations of Uranus — before anyone had seen it.
Every opposition in the Celestial Calendar. Countdown, viewing notes, shareable cards. Energy Layer members.
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