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Tomorrow the “green comet” will reach its closest approach to Earth

Tomorrow the “green comet” will reach its closest approach to Earth

Green comet
Comet c/2022 E3 (ZTF) imaged from the Dark Sky® Observatory, in Alqueva, Portugal on January 19, 2023. Author: Miguel Claro. Source:

Tomorrow, Wednesday (February 1, 2023), the “green comet” will make its closest approach to Earth: about 42 million km. It’s been a few days now visible to the naked eye (as an astronomical object of magnitude +5) 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 vision in the night sky, the human eye can observe stellar objects with magnitudes up to +6.

It is already visible to the naked eye as a +5 magnitude astronomical object, with the human eye capable of observing stellar objects up to +6 magnitude.

The comet began to be called “green”, because this is the striking color of its coma (the gaseous cloud surrounding its nucleus) in astrophotography. The object is cataloged as c/2022 E3 (ZTF).. The reference to the year 2022 is due to the fact that It was discovered last year (March 2) by two American astronomers using the Wide Field Camera at the nearby Palomar Observatory San DiegoCalifornia, USA, as part of an automated sky-watching program called Zwicky Transit Facilityhence the acronym ZTF, which also includes the technical name of the comet.

The comet’s nucleus is less than two kilometers in diameterbut as it got closer to the Sun (it reached perihelion on January 12), it began to become more visible than Earth, thanks to the separation of several tails several million kilometers long.

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The comet has an eccentric orbit The last time it came close to Earth was at least 50,000 years ago, during the last glaciation, when Europe It was inhabited by Neanderthals (now in decline) and Homo sapiens. It is interesting to know that during some of the cold, dark nights of that time, our ancestors saw the same green comet in the sky.

Comets throughout history

The fact is that hundreds of comets have appeared in the sky throughout human history. For a long time they were interpreted as harbingers of misfortune. in Greece age or old, Aristotle, in his treatise “Meteorologicos” (4th century BC) wrongly attributed the nature of the atmosphere to them (contradicting the ideas of other Greek philosophers such as Democritus), and this error persisted for several centuries, until we finally realized, thanks to the development of astronomy, that they were bodies of extraterrestrial origin that crossed the universe.

The great comet of 1577
The Great Comet of 1577, seen in Prague on November 12 of that year. Engraving by Jerry Dashetsky. Source: Wikipedia

According to Aristotle, comets formed in the sublunar region.which was one of the regions into which the sky was divided in ancient times, with the regions associated with each of the four primary elements of nature (air, water, earth, and fire) below, and the spheres of the planets and the vault of the starry sky above.

It was only in the sixteenth century After the passage of the great comet in 1577, the Danish astronomer Thicho Brahe (1546-1601) correctly deduced that this and other comets were astronomical bodiesperiodically coming close to Earth, as is currently the case with Comet c/2022 E3 (ZTF).

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How do we observe a “green comet” (ZTF)?

As we pointed out, although the comet was only visible for a few days in the northern hemisphere, Light pollution in our cities and the presence of the moon in part of the morning makes it difficult to detect with the naked eye The “little cloud” (a small spot of diffused light) 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 monitor it successfully, the first thing to do is Far enough away from cities or population centersLooking for the darkest sky possible. It is also necessary Avoid lunar hours, which we must get up early, and observe in the two to three hours before dawn. Of course, the sky must be clear, which is guaranteed this week in almost all of Portugal. We’ll have to direct our gaze (binoculars or a telescope) to the north, precisely 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 Auriga (The Charioteer), and on February 5th it will be very close to the bright star Capela.