Comet 3I/Atlas reaches its closest point to Earth: how to see it and what to expect

The interstellar comet 3I/Atlas is finally approaching Earth. This means that on December 19, the third object, confirmed to be from another star system, will enter the stage of best observation. Scientists and astronomy enthusiasts will be able to observe it with the highest possible resolution and understand its mysterious behavior. At WIRED en Español, we have prepared this guide with all the necessary information about it.

Close, but not that close

It is desirable to qualify it as the “closest point” to our planet. According to the calculations of space agencies such as NASA or ESA, 3I/Atlas will reduce its distance to 270 million kilometers. For comparison, this is almost 700 times greater than the distance between the Earth and the Moon. This is even more than the average distance of Mars, calculated at 225 million kilometers. The object is at a considerable distance from the planet, which eliminates the risk.

A basic schematic of the 3I/ATLAS comet location during December 19. From now on, the object will only move away. Image based on NASA simulations.

Rodrigo Mead/WIRED in Spanish. Based on NASA’s Eyes on the Solar System.

It is a comet 10 to 30 km in diameter with a corresponding tail and gaseous atmosphere. Its brightness in the sky will be very low compared to stars or planets visible at night. It is impossible for you to find it with the naked eye.

On the brightness scale, its magnitude is +11. The image places it on the list of stellar objects that can be seen in medium telescopes with an aperture of 250-300 mm and powerful 25×100 binoculars, for example, stars in globular clusters or at the bottom of the Milky Way. When you use one of these devices, you’ll see a glowing “cloud” instead of a well-defined bright spot. If you were lucky, you could see the tail.

How to see Comet 3I/Atlas?

The window of greatest observation of the interstellar comet is the early morning of December 19 in the area of ​​the constellation Leo. He will be next to Regulus, the brightest star in Leo. At night, this constellation is 20 to 40° above the horizon, in the east or northeast. In other words, don’t look up, but look relatively close to the line that separates the earth from the sky. Consider that if you place your palm vertically above the horizon, you will calculate 20°.

Of course, you should stay away from any artificial light sources and go to a high place so that you can gaze at the horizon unhindered. Fortunately, the next day is a new moon, so we’re in for a pretty dark night. Your telescope or binoculars should have a good support to prevent them from accidentally moving.

Schedule for viewing 3I/Atlas

• Mexico City: The optimal window is from 02:00 to 04:30 on December 19. The Leo constellation will be in the east-northeast direction, at 20 and 30°.
• Los Angeles: The optimal window is from 01:00 to 04:00. The Leo constellation will be in the east-northeast, at 20 and 30°.
• Madrid: The optimal window is from 05:30 to 07:30, almost at dawn. The Leo constellation is in the east at 25 and 40° altitude.

And what’s next with the comet?

Last month, NASA confirmed that 3I/Atlas is a natural body and ruled out a technological interpretation. He also recognized that its composition is unique in the solar system. Astronomers will aim their instruments at the comet to confirm some assumptions and provide new knowledge for models of planet formation.

Remember that since November 27, the International Asteroid Warning Network has begun active monitoring, which will end on January 27, 2026. In general, no transcendent discovery is expected, apart from what has already been studied. The best images will be published in official sources.