Everything you need to know about the visit of the green comet

is

not the comet of the century, but it does provide a nice spectacle, especially when viewed with binoculars or a small telescope.

Here we offer you all the details to enjoy this astronomical event.

Green and with three tails

Reading some headlines in the press, one might think that we are facing the comet of the century.

And no, to the naked eye it is not a dazzling green comet, nor spectacular, nor even very striking.

To see it well you have to use binoculars or a small telescope.

But

us, it reminds us that the sky is not immutable, far from it.

In the case of the

(

in astronomical jargon), we are excited to think that its last visit took place in the Upper Paleolithic, in the time of the Neanderthals, and that, if it returns, it will not come close to Earth again

.

The excellent images that accompany this article have been obtained on January 19 and 23, respectively.

The first was taken by comet specialist Pepe Chambó from his small domestic observatory in Vallés, near Xàtiva (Valencia).

While the second was obtained by astrophotographers Julián García and Alfonso Espinosa from the Astroguada association [astroguada.com] during a very cold night (8.5 degrees below zero) from Miralbueno (Guadalajara).

In them we can appreciate

(see below).

In the image taken by Chambó, the ionic tail is displayed in all its splendor towards the lower left, while the more diffuse and shorter dust tail can be seen in the lower part of the head.

The anti-tail, which has become more prominent in more recent days, can be seen well to the right of the image taken by García and Espinosa.

The ZTF observed from Mirabueno on January 23. Alfonso Espinosa and Julián García

Observation Guide

These days, the comet's visual magnitude is between 7 and 6, meaning it can be seen with the naked eye, but with difficulty.

After passing

, it moves very quickly in the sky.

It is now in Camelopardalis and in the first half of February it will cross Taurus.

At the beginning of February, the comet remains in circumpolar positions (near the north celestial pole), that is, it is observable throughout the night.

In the first hours of the night, we can see it very high on the horizon to the northwest.

On the weekend of February 4 and 5, the full moon will make observation difficult, but on successive days, we will be able to take advantage of the hours at the beginning of the night, before the Moon rises, to enjoy a dark sky.

On February 6 our visitor will glide near Capella,

.

On the 11th it will be very close to Mars, offering wonderful opportunities for astrophotographers to capture snapshots that capture the beautiful contrast of cometary green with Martian red-orange.

Trajectory of the ZTF.starwalk.space

By

(February 14) the ZTF will have dimmed a lot as it recedes from us on its long journey back to the dark reaches of the solar system.

And we are not sure that it will be seen again in these places because, due to the disturbances that the planets (mainly Jupiter) have introduced into their orbit, the comet may no longer be periodic.

In any case, what is certain is that our eyes will never see it again.

Orbit

The ZTF is so named because it was discovered with the '

', a large field of view telescope equipped with a 1.2 meter mirror, on Mount Palomar (California, USA).

Since its first sighting, on

, the comet gradually increased in brightness as it approached the Sun. It is relatively easy to calculate a comet's orbit, just measure its position in the sky a few times.

In this way, it was learned that the comet was periodic and that, from the Oort cloud, in the depths of the solar system, it visits us every 50,000 years.

It reached perihelion (its closest position to the Sun) on January 12, when it was only 166 million kilometers from the star king, and its closest approach to Earth occurred on February 1, when the comet

(to orient yourself with these distances, remember that the Earth-Sun distance is 150 million kilometers).

Comet orbit ZTF.NASA/RB

Two tails and one antitail

Due to their composition, which includes ice, rock and dusty material, comets are often referred to as '

'.

As a comet approaches the Sun, the action of solar radiation and the solar wind causes the ice to sublimate and gases and dusty material are expelled into space, forming a coma (a kind of atmosphere around the cometary body) and some long lines.

Comets usually have two well-defined tails.

The tail of ionized gas, created by the sublimation of the ice, points exactly in the opposite direction to the Sun, it is the longest tail in the image taken by Chambó that accompanies this article.

one and is somewhat curved since the movement of this solid material is affected by orbital inertia.

The dust tail is therefore located between the gas tail and the comet's orbit.

In addition,

, so called because it appears in the opposite direction to the two previous tails (ionic and dust), that is, pointing approximately towards the Sun. The anti-tail is a projection phenomenon, it is formed by the particles that lie in a disk in the comet's orbital plane when viewed from a favorable perspective from Earth.

The anti-tail can be seen very clearly in the image taken by Espinosa and García (presented above).

molecular turquoise

The pretty turquoise, teal color of Comet ZTF, which

, is not unique to this visitor.

In fact, this color is observable in many of the comets that travel towards the inner region of our planetary system.

Ultraviolet radiation from the Sun dissociates the organic molecules that abound in that dirty snowball to produce vast amounts of diatomic carbon, and the further destruction of these molecules (which have a half-life of a couple of days)

.

So we see that the emission of this light occurs in the head of the comet, but not in the main tail (where the material is ionized).

In any case, this bluish-green color is not appreciable with the naked eye.

science and myth

Comets have been associated with numerous superstitions throughout history and were often considered to bring bad omens.

The great astronomer

(1546-1601) was the first to consider them scientifically, concluding that they were phenomena not associated with Earth.

Paradoxically, far from being birds of bad omen, comets have starred in great moments in the history of science.

Suffice it to recall Halley's prediction, several years in advance, that

.

The punctual arrival of the comet was in its day a spectacular triumph of Newton's theory of gravitation.

Even today,

, as well as the visits of all the periodic comets that keep their appointments punctually, offer us one of the most beautiful illustrations of the predictive power of science.

Rafael Bachiller

is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.

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