Neptune at opposition
Neptune reaches opposition when Earth passes between the sun and the 8th planet Neptune.
As the sun and Neptune are on opposite sides of the Earth during opposition, they appear on opposite sides, or 180° apart, in our sky.
As a result, Neptune rises in the east when the sun sets in the west, reaches its highest point in the sky at midnight when the sun is below your feet, and sets in the west when the sun rises in the east.
Neptune is best visible around opposition
Neptune at opposition marks the best time to see the outer planet, as it’s visible throughout the night under clear skies. More precisely, it signifies the middle of the best time of the year to observe the planet.
After opposition, Neptune disappears from the morning sky gradually as it rises and sets four minutes earlier each day.
So, one month after opposition, Neptune rises 4*30 minutes = 120 minutes = 2 hours before sunset and sets 2 hours before sunrise.
So, three months after opposition, Neptune is visible in the evening sky only as it rises 6 hours before sunset, i.e., at noon, and sets 6 hours before sunrise, i.e., at midnight.
Neptune is closest, largest and brightest around opposition
Neptune is closest to Earth around the time of its opposition because the sun, Earth, and Neptune are all lined up in a straight line, and Neptune is located on the same side of the sun as Earth around the time of its opposition.
Neptune at opposition and the closest approach of Neptune to Earth would occur at the same time if the orbits of Earth and Neptune were perfectly circular.
Neptune appears largest and brightest in our sky around the time of its opposition, as it marks the closest approach of Neptune to Earth.
Neptune at opposition in 2025
Neptune will reach opposition on September 23, 2025, at 11:00 UTC (7 a.m. EDT).
Best time to see Neptune in 2025: Neptune will be best visible from early September through early October in 2025, when the planet rises in the east around the time of sunset and is visible all night.
Closest approach of Neptune to Earth in 2025: Neptune will be closest to Earth on September 23, 2025, i.e., on the day of its opposition in 2025. During the closest approach, Neptune will be 28.88 A.U., i.e., 4.32 billion km away from Earth.
Brightness at opposition: At its September 23 opposition, Neptune will be brightest for 2025 and will shine with a magnitude of +7.8.
Disk size at opposition: At its September 23 opposition, Neptune will be largest in size for 2025 and will appear 2.4 arcseconds in diameter through a telescope.
Constellation at opposition: At its September 23 opposition, Neptune will be located in the zodiac constellation Pisces, the Fish.
How often does Neptune reach opposition?
Neptune takes about 165 Earth years to orbit the sun once. So when our Earth makes one full orbit around the sun, Neptune travels 1/165 of the way around the sun. So to create Neptune’s opposition, our Earth would have to travel an extra 1/165 of the way in its orbit, which takes about (1/165)*365 = 2 days to travel.
That’s why planet Neptune reaches opposition once every 1 year and 2 days, or 367 days.
Dates of Neptune’s opposition
Here are the dates of Neptune’s opposition from 2025 to 2029, according to NASA:
| Date of opposition | Date of closest approach | Distance of closest approach (A.U.) |
|---|---|---|
| September 23, 2025 | September 23, 2025 | 28.88 |
| September 26, 2026 | September 25, 2026 | 28.88 |
| September 28, 2027 | September 28, 2027 | 28.87 |
| September 30, 2028 | September 29, 2028 | 28.86 |
| October 2, 2029 | October 2, 2029 | 28.86 |
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