As the farthest planet in our solar system (sorry, Pluto), Neptune is a rare sight in the night sky. But if you want to see the ice giant in 2021, look up on Tuesday, September 14. On that date, Neptune will reach opposition, making it appear especially big and bright from Earth. Here's what you need to know to catch the event.
What Is Neptune at Opposition?
Opposition describes a planet's position in relation to the sun and Earth. When Neptune perfectly aligns with these two bodies, it reaches opposition. The Earth falls in the middle of this alignment, and from our planet we can watch the sun's light fully illuminate Neptune's surface. The royal-blue dot is usually shrouded in the darkness of our solar system, but on September 14 it will be visible with the aid of binoculars or a telescope.
Neptune's opposition coincides with its perigee, or the point in its orbit when it comes closest to Earth. So not only will the planet look relatively bright that night, but it will appear larger than usual as well.
How to See Neptune at Opposition
Neptune will rise around sunset on September 14, 2021, and dip below the horizon close to dawn. At approximately midnight local time, it will be in its highest point in the sky's dome. Around midnight is also when the quarter moon will set, leaving behind dark skies and optimal viewing conditions.
When searching for Neptune, look for Aquarius. The eighth planet should appear directly in front of the water-bearer constellation and close to the star Phi Aquarii. Though Neptune will be visible on September 14, it will still look faint compared to the surrounding stars. Neptune is the only true planet in our solar system that can't be seen with the naked eye any time of year. Bring some type of magnifying equipment to look for Neptune, and refer to a sky chart if you lose your bearings.