Tomorrow, Wednesday (February 1, 2023) the “green comet” will reach its closest approach to Earth: about 42 million kilometers. It’s been a few days now visible to the naked eye (as a stellar magnitude +5 astronomical object) from the northern hemisphere, and over the next few days it will also become visible to the naked eye from the southern hemisphere. Under optimal conditions of visibility in the night sky, the human eye is capable of observing stellar objects up to magnitude +6.
It is already visible to the naked eye as an astronomical object of magnitude +5, with the human eye capable of observing stellar objects of magnitude up to +6.
The comet began to be called “green”, as this is the striking color of its coma (the gaseous cloud that surrounds its nucleus) in astrophotographs. The object is cataloged as c/2022 E3 (ZTF). The reference to 2022 is due to the fact that have been discovered last year (March 2) by a pair of American astronomers, who were using a wide-field camera at the Palomar Observatory, near San Diego, California, in the US, as part of an automated sky observation program called Zwicky Transient Facilityhence the acronym ZTF, which also includes the comet’s technical name.
Why is the comet that reappeared after 50,000 years green?
The comet’s nucleus is just under 2 kilometers in diameterbut when it approached the Sun (it reached its perihelion on January 12), it began to become more visible from Earth, thanks to the detachment of several tails that reach several million kilometers in length.
The comet has a very eccentric orbit and the last time it approached Earth was no less than 50,000 years ago, during the last glaciation, when Europe was inhabited by Neanderthals (now in decline) and homo sapiens. It’s exciting to know that during some cold, dark nights back then, our ancestors saw this same green comet in the sky.
Comets throughout history
The truth is that hundreds of comets have appeared in the sky throughout human history. For a long time they were interpreted as harbingers of calamity. In Ancient Greece, Aristotle, in his treatise “Meteorologicos” (4th century BC) mistakenly attributed an atmospheric nature to them (contradicting the ideas of other Greek philosophers such as Democritus), and this error continued for many centuries, until finally, thanks to the development of Astronomy, we understood that they were objects of extraterrestrial origin that crossed the cosmos.
According to Aristotle, comets formed in the sublunar region.which was one of the regions into which the sky was divided in classical times, with the regions associated with each of the four basic elements of nature (air, water, earth and fire) below, and the spheres of the planets and the vault of heaven filled with of stars above.
It was only in the sixteenth century that after the passage of the Great Comet of 1577, the Danish astronomer Thycho Brahe (1546-1601) correctly deduced that this and other comets were astronomical objectsperiodically approaching Earth, as is currently the case with comet c/2022 E3 (ZTF).
How to observe the “green comet” (ZTF)?
As we indicated, although the comet has been visible for a few days in the northern hemisphere, light pollution in our cities and the presence of the moon during part of the morning make it difficult to observe with the naked eye the “little cloud” (a small patch of diffused light) that we can appreciate, so it is advisable to use binoculars (mounted on a tripod) or a small telescope, in which case we can see its long tail.
To observe it successfully, the first thing to do is far enough away from cities or population centers, looking for the darkest sky possible. It is also necessary avoid moon hours, for which we must get up early, and carry out the observation during the two to three hours before dawn. Of course, the sky must be cloudless, which this week is guaranteed in virtually all of Portugal. We will have to direct our gaze (binoculars or telescope) to the north, specifically to Ursa Minor. We’ll see the comet not far from its brightest star, Polaris.although in the next few days it will move away towards the neighboring constellation of Auriga (The Charioteer), and on February 5th it will be very close to the bright star Capela.