(CNN Spanish) – One of the astronomical phenomena that occur once a year is Neptune in opposition and September is the month to witness it. The eighth planet of the solar system will be visible from Earth with a brightness that it does not have very often.

What is Neptune in opposition?

Let's first talk about the concept of opposition.

An astronomical opposition occurs when a planet is opposite the Sun. For example, when Saturn is at opposition, Earth is between the Sun and Saturn, according to Royal Museums Greenwich. From Earth's perspective, it means that an opposing planet is precisely 180 degrees from the Sun in the sky, so when the Sun is in the west, a planet appears in the east.

EarthSky explains it very simply: it is as if a person was standing between two friends while talking in the supermarket and had to turn his head in half to see one and the other.

Neptune in opposition means that the planet will be opposite the Sun and the Earth will be in the middle of both.


Because an opposition only occurs when our planet is between the sun and another celestial body, this phenomenon occurs with the planets farther from the Sun than Earth: Mars, Jupiter, Saturn, Uranus and Neptune.

Mercury and Venus cannot be in opposition, according to EarthSky.

The oppositions of the planets occur once a year, when the Earth reaches the proper position with the planets relative to the Sun. Mars is the only exception because its orbit and speed are similar to those of Earth, so that our planet surpasses the red planet every 27 months or so.

When will Neptune be in opposition?

The Earth will pass between the Sun and Neptune next Tuesday, September 19. According to EarthSky, at the time of its opposition, the blue planet will rise in the east at sunset and will be visible all night.

At its peak from Earth, Neptune will be just 240 light-minutes away, its shortest distance all year, and will have a brightness of magnitude greater than 7.8, which will also be its 2023 maximum.

Their opposition is special because this planet is never really bright. In fact, it's about five times fainter than the faintest star seen on a moonless night under a dark sky, according to The Old Farmer's Almanac.

The phenomenon will reach opposition at 7 a.m. Miami time, according to Earthsky. However, it will be visible much of the night of September 18-19.

In Mexico, the opposition time will be at 5 a.m., while in Colombia it will be at 6 a.m., and in Argentina at 8 a.m.

How to see it?

According to experts, in order to see the blue planet you will need optical help. It can be a low-power telescope or binoculars.

The planet will rise in the east and set in the west at dawn. With the help of a telescope, Neptune will appear with 2.3 arcseconds in diameter, while with binoculars it will be visible as a star-like object, according to EarthSky.

It is also possible to make use of some mobile applications to be able to witness the phenomenon. Starwalk recommends using Sky Tonight, which allows you to search for the name of the object and through a compass that you must move in the right direction you can see the planet on the screen.

Next competitions in 2023

  • Jupiter at opposition: November 3.
  • Uranus in opposition: November 14.

Fun facts about Neptune

- It was discovered on September 23, 1846.

It has 14 moons, two of which orbit at a staggering distance of 50 million kilometers and are considered the farthest moons of any planet. They are even farther from Neptune than Venus is from Earth, according to The Old Farmer's Almanac.

It has the windiest climate in the solar system, with fierce winds and clouds of frozen methane blowing five times faster than tornadoes.

- It is named after the Roman god of the sea because of its ocean-blue color, but that hue is a mystery because its large amount of methane gas should make it green, like Uranus.

- It has the coldest surface in the entire solar system with an average temperature of -214 ° C.

- It is also very dark. A noon on Neptune is as bright as a sunset on Earth.

- The length of its days is 16 hours, a year lasts 165 Earth years, which means that from its discovery until today barely a year has passed.

It takes 12 years to travel in space from Earth to Neptune.