The photo featured on the Astronomy Picture of the Day website this Tuesday (31) shows a curious feature of comet C/2022 E3 (ZTF). Pictured are its greenish coma, the ion and dust tails, and… a “third” tail.
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Usually, comets have only two tails, but different photographers have been recording the “anti-tail” of comet ZTF, the name given to the other that appears in the photos. It is formed by the same material present in the tails of other iobjects of the type and, in fact, it is nothing more than an optical illusion.
This “anti-tail” is formed by our perspective of observing the comet. As Earth moves through its orbital plane, some of the dust in the ZTF’s path is illuminated by the Sun, and the viewing angle gives the impression of a third tail there.
In the picture, the comet appears as it did in naked-eye observations in a region of dark skies and away from light pollution. The highlighted frame at the top shows how an observer would see it with binoculars, and at the bottom, with a small telescope.
What are comets?
In short, we can say that comets are frozen objects, accompanied by gases, rocks and dust left over from the formation of the Solar System, which occurred about 4.6 billion years ago. They travel around the Sun in highly elliptical orbits, and it can take thousands of years to complete a single loop around our star.
As the Sun’s gravity pulls them in, comets make a “turn” behind it and then head back toward their point of origin—and as they travel through the inner Solar System, they can be seen from Earth. Sometimes, the encounter with the Sun can be fatal: some comets can dive into our star and are never seen again.
The “Green Comet”, nickname by which the ZTF became popularly known, last approached Earth 50,000 years ago. Its closest approach will occur on February 1, when the comet will be about 42 million kilometers from our planet.