The green comet ZTF has increased in magnitude and can now be seen with the naked eye

Comets have always fascinated humanity and remind us that we cannot live outside of our cosmic environment. During the last nights of January in the northern hemisphere and the first nights of February in the southern hemisphere, we have the opportunity to observe a comet from the depths of the Solar System, cataloged as C/2022 E3.

It is a new comet, never before observed or, at least, in our written history. ZTF, popularly known as “green kite”, has increased its luminosity.

We’ve been tracking him for months. It was discovered almost a year in advance by astronomers Bryce Bolin and Frank Masci on March 2, 2022 using the wide-field camera at the Zwicky Transient Facility in the United States (hence the acronym that gives the comet its name: ZTF). .

Based on the observations made by hundreds of professional and amateur observatories around the world, it has been possible to measure the movement of the comet in the sky and reconstruct its orbit in the Solar System.

Its closest step to the Sun

The comet that visits us follows an eccentric orbit that it completes every 50,000 years. The observations made by our research group at the Institute of Space Sciences (CSIC) and the Institut d’Estudis Espacials de Catalunya (IEEC) show that its luminosity has increased in recent nights and for a few days we will be able to observe it with the naked eye before that it returns to its dark and remote corner in the outer Solar System.

ZTF has just passed through its perihelion, the closest point in its orbit to the Sun, on January 12. At that time, the solar irradiation of its surface was maximum, and produced the sublimation of the ice that makes up part of its structure. That is why it has increased its luminosity.

When the ice that is part of the comet sublimates, they expel jets of gas that carry dust particles that can measure from micrometers to centimeters. The gas and dust emissions vary according to the exposure of the ice of the cometary nucleus, which is why they are capricious stars, with an often changing appearance.

The tails of the ZTF comet that can be observed

As they approach the Sun, comets develop an envelope or hair that we call eat.

ZTF has a core possibly a few kilometers in diameter and has developed the two characteristic tails of these stars. The finest and most imperceptible is the call ionic or plasma glue. This is usually quite straight and extensive, sometimes showing multiple striations and, as the top image of this report shows, it looks bluish. This tail is the result of the emission of light from ionized molecules that are ejected in the opposite direction to the Sun and that result from the interaction between the emitted gas and the powerful solar wind.

The tracking photographs that we have taken show this thin tail extended several degrees (two full moons together would represent one angular degree), always in an antisolar direction. Both visually and through binoculars or a telescope, this ionic tail is very difficult to see, because it is so faint.

The second tail of the comet, the dust tail, yellowish or orange in the images taken from the Parc Astronòmic Muntanyes de Prades, is more visible and extends quite far from the comet’s coma.

Close to stellar magnitude +5

Observations of the comet made on January 26, 2023 indicate that it is close to stellar magnitude +5 and is therefore already visible to the naked eye from a place with little artificial light.

This is its apparent trajectory in the sky for the next few weeks and our recommendation is to try to observe it in the next few days, before the moonlight makes it more difficult to see.

Trajectory between the constellations of the ZTF comet from mid-January to February 6. The celestial chart briefly indicates the names of the main constellations: Auriga (AUR), Cepheus (CEP), Dragon (DRA), Ursa Major (UMA), Ursa Minor (UMi), etc…
Author provided

Comet ZTF will be very well positioned from the Northern Hemisphere, and will become circumpolar (visible all night) during the last two weeks of January and the first of February. In that first week of February it will begin to be seen from the southern hemisphere.

It will pass close to the Polaris star on January 30 and close to the bright Capella on February 6, moving with a very fast angular velocity during the days closest to Earth.

The comet’s current location among the constellations can be quickly seen on the sky chart provided by The Sky Live.

Since it is not much brighter than any of the stars we see at our visual limit, it is advisable to use 7×50 or 12×50 binoculars.

Increased internal activity of the nucleus

In our latest observations we appreciate a significant increase in the internal activity of the nucleus, which indicates an increase in the dust emitted from the active regions. This entails a progressive increase in the luminosity of the comet’s coma that is currently visible to the naked eye.

The false core of the comet seen with a telescope is active and has intensified its activity, as revealed by the presence of large jets of gas emitted from the active regions. These latest observations point to the fact that the comet’s luminosity is maintained for the next few days when it gets even closer to Earth.

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Image of the ZTF comet recorded from the Montseny Observatory on January 23.
JM Trigo-Rodriguez / CSIC-IEEC, Author provided

Fortunately these fast visitors have plenty of space between the planets to spread their tails and surprise humans without posing a danger. However, let us not pretend to remain oblivious as every few hundred million years someone of kilometric size could have cards to hit the Earth. Precisely for this reason we must continue looking up with our modern telescopes and continue equipping ourselves with automated search programs that allow us to discover in time, and to be able to define with precision, the orbits of wandering stars.

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