Let’s watch The Green Comet: And commune with our black ancestors!

“Beautiful,” the bearded Italian offered, after a fuzzy sphere of light— with faint rays streaming from it—appeared on the black screen. “Very beautiful. A very rewarding experience.”

Gionluca Masi, founder of Virtual Telescope Project 2.0, was elated. He’d been tinkering with the telescope’s controls for some time, trying to conjure the apparition—as Online viewers watched, raptly. I among them.

Finally, his cursor was poking at a radiant sphere: The Telescope’s real-time depiction of comet ‘C/2022 E3 (ZTF)’, which has been careering through the inner solar system, since its discovery last March.

This was January 14th; and the globally-heralded visitor from deep space, had just rounded the Sun. Having reversed direction, it is now hurtling outward again; and will make a critical flyby of Earth, February 1 and 2.

The flyby, is both promising and potentially problematic. If the promise holds, we may be feted to an enthralling celestial display—a green-hued visual aesthetic, last seen in Earth’s skies 54,000 years ago (if at all).

But first, the global media have been spinning ZTF, as a ‘rare green comet’— which is misleading. Green comets aren’t rare. ISON (2013), NEOWISE (2020), Lovejoy (2017) and Machholz (2005) had green heads.

Perhaps I should digress, here, and explain what a comet is. Imagine the ice tray, in your fridge. Its cubes, can be thought of as ‘comets’— which are chunks of ice, with dust grains, pebbles and various gases frozen into them.

Trillions of such chunks orbit the Sun far out, at the solar system’s edge, in two cosmic ‘deep freezers’— the Oort cloud and Kuiper Belt. Ongoing tidal disruption, keeps them streaming inwards, towards the Sun.

“These ejected planetoids,” averred professor Tunde Rabiu, director of the African Regional Centre for Space Science and Technology Education, at Il-Ife “are astronomical fossils, relics from the solar system’s formation.
“We should develop a keen interest in comets,” Rabiu urged, because “the Oort cloud and the Kuiper Belt are cosmic ruins. Their contents, can yield invaluable insight into the past of our star, the Sun, and its planets.”

The chances of an orbital “fossil” entering our field of view, depends on where it came from. Short period comets originate in the Kuiper Belt. They loop round the Sun, in return cycles of 200 years, or less.

But these frequent visitors, normally arrive unseen. A famous exception, is 1P/Halley. With a 76-79-year period, it is, as Wikipedia notes, the “only naked-eye comet certain to return within a human lifetime.”

Long period comets, with cycles of 200-plus years, originate in the Oort cloud and are very bright: E.g., Wikipedia’s 34 ‘Great Comets’, (which includes Hale-Bopp, with a 2,300-year cycle; and Hyakutake, 70,000).

Hence, ZTF’s visit—if not its colour—is rare, indeed! When it last blew pass Earth, heading back to the distant Oort Cloud, Africans had colonized Europe and Asia, invented artificial fire and given Earth its first language!

Sadly, I must say, some progeny of those Africans—who used astronomy to explore the planet—are impervious to the allure of ZTF. Its appearance, could even inspire fear and dread, in them, rather wonder and curiosity.

“Unfortunately,” concedes Dr. Halilu Ahmad Shaba, director general of the National Space Research and Development Agency (NASRDA), “many ill-informed Nigerians do hold beliefs, which can threaten social stability.
“That’s why,” he continues, “NASRDA is collaborating with the International Astronomical Union’s Office of Astronomy for Development — to help cultivate refined minds, that can appreciate celestial events.”

Yet, ignorance and fear of celestial phenomena, is by no means unique to Nigeria. Sages and seers—ancient to modern—have portrayed the night sky, as a repository of egregious ‘spiritual forces’, ever-ready to wreak havoc.

The word ‘disaster’, for instance, stems from the Old Italian ‘disastro’—meaning ‘ill-starred’. It is, the Merriam-Webster dictionary notes, rooted in the belief that stars influence human fate, “often in a destructive way.”

Eclipses and comets, in particular, were widely feared. “In Africa, as in Europe,” writes D.J. Schove, in “Eclipses, Comets and the Spectrum of Time,” astronomical portents signify “plagues and other calamities.”

A famous story in The Times Gazette (U.S.A.), reported that when Halley’s Comet appeared in 1910, the police narrowly prevented a white religious cult, in Oklahoma, from sacrificing a 16-year-old virgin!

Also, many readers will be old enough to remember the 1997 Heaven’s Gate suicides in Southern California. Thirty-nine people died, following the appearance of Hale-Bopp—a brilliant naked-eye comet.

If ZTF crosses the naked-eye threshold, that will be during the flyby—when it careens, to within 4.3 million km of Earth. Astronomy.Com, says the departing comet will continue to brighten, and “peak around Feb 1…”

Presently, one needs a small telescope—or at least a pair of binoculars—to see the apparition. Nevertheless, most projections allow for the possibility that February 1 and 2, will find ZTF radiating at magnitude ‘5’.
‘Five’, is the optical brink on the magnitude scale, which measures apparent brightness. At this level, the comet would appear as a luminous smudge, instead of a visual extravaganza, like Hale-Bopp or NEOWISE.

ZTF is small, as comets go. With a 1-km wide nucleus, it is not in the league with NEOWISE (five km) or Hale-Bopp (60 km)—and is far below the solar system average, of 10 km.

This does not mean, though, that sky-watchers should sit, wringing their hands, in despair. Quite to the contrary, avers NASRDA’s Shaba, “there is something of value, to take away from every sky-watching experience”.

Besides, size alone, is not the sine qua none of visibility. Comet 2014 UN271, a 2031 arrival, for example, has a 137 km nucleus–the biggest of any Oort cloud comer! Yet, astronomers say it won’t be a naked eye object!
“What this implies,” explains Dr. Bonaventure Okere, director of NASRDA’s Centre for Basic Space Science (CBSS), at Nsukka, Enugu State, “is that a comet has other properties, that help account for its visibility.”

One, he says, is ‘outgassing’. In their pristine (Kuiper Belt/Oort cloud) state, comets are icy bodies encrusted with a coal-black coating of complex organic compounds; and are among the darkest objects in the solar system.
“A comet becomes luminous,” Okere explained, “only as it approaches the Sun. Solar radiation, heats the encased ices, causing them to sublime—i.e., change directly from a solid to a gas.”

Six spacecraft, have photographed jets of gas and dust, exploding through weak-spots and openings in the dark crust of various comets. On average, investigators report, only about 10 per cent of the surface is breached.

The jetting of gases and grains, through these breaches, create the visual effects—the archetypal “comet” structure—we perceive. First, a reflective atmosphere, called the “coma,” radiates, spherically, from the nucleus.

ZTF derives its identity, as a ‘green-headed’ comet, from the diatomic carbon in its atmosphere. Solar radiation breaks the green-glowing molecules up, into single atoms, before they can escape the coma.

Otherwise, astronomers postulate, the two-atom carbon molecule would migrate to the comet’s tails—causing them to also appear ‘green’. The ‘tails’ are long luminous bifurcations, that usually extend from the coma.

It is the striking geometry, and visual aesthetics, of these iconic structures, that make comets such a potent emotional trigger: Evoking passions, that range from consternation to enthralled fixation.

Two tails form, theory holds, when the nucleus—traveling in mufti (hidden in a fuzzy coma) — approach the orbit of Mars. The pressure of sunlight and the solar wind, sweeps dust and ionised gases from the coma.

The ions,” explains David Jewitt, an astronomer at the University of California, Los Angeles, “are swept out of the coma into a long… tail,” which the solar wind orients, “almost exactly in an anti-solar direction.”

Visually, the long, straight ion — or ‘Type I’—tail frequently appears ‘blue’, to the human eye: Because “the most common ion, CO+ [carbon monoxide], scatters blue light better than red.”

By contrast, the dust—or ‘Type II’— tail is curved and often white or slightly pinkish, in appearance. Jewitt’s explanation, is that the dust grains are better at reflecting longer (reddish) wavelength of light, back to Earth.

Finally, he attributes the Type II (dust) tail’s curvature to orbital mechanics—since each individual particle is in orbit around the Sun.

The dust tail, thus follows a curved trajectory, just as the comet does.

As comet ZTF approaches perigee (its closest to Earth), on 1 and 2 its brightness is presumably — and hopefully — escalating. Whether it increases to naked-eye magnitude is, at this point, a “wait-and-see” situation.

Much will depend on your location, cloud conditions and the vagaries of the comet itself. No matter what hand fate plays, though, a resourceful and determined sky-watcher can, nowadays, always stay in the game.

The viewing is best, astronomers advise, in a dark area, away from streetlamps. Then, if the sky is clear and the comet if faint, you might wish to try “averted vision” —a technique starwalk.com recommends.

I’ve never tried it. But you may find it helpful, the website says, ‘with or without’ a viewing aid:
Pick an object you want to see.
Locate the object in the sky. A stargazing app will help you here — you can use the Sky Tonight app… for free.
Once you’ve located the object, place it at about 8° to 16° away from the eye’s center (i.e., from a side view, rather than direct).
In your field of view, keep the object nearer to your nose than to the side of your face.
This way, you won’t let the object fall on the blind spot on the side of the eye.
If you’re using binoculars, point your gaze above the object instead of looking to the side.

Looking only sideways makes one eye more sensitive at the expense of the other.
Don’t give up if it doesn’t work immediately. Using averted vision on purpose is a lot more complicated than it looks. –Starwalk.com

Meanwhile, if all else fails, or an outdoor event simply doesn’t excite you, the Virtual Telescope is always an option.

Either way, watching the same comet our prehistoric ancestors may have seen, 54,000 years ago would, as Gionluca Masi would say, be “a very rewarding experience”!