Green comet passerby can inspire deeper cosmological thoughts
Over the past several days, reports have emerged that Earth will be visited by a passerby from the outermost reaches of the solar system in the coming days. A comet, an agglomeration of ice and dust streaking through the sky and carrying behind it a luminous tail, is currently headed our way.
It's nothing to be concerned about, though, as the nearest point to Earth along the object's path is 26 million miles (41.8 million kilometers) away from us.
However, in terms of cosmological distances, this is extremely close; in fact, it's the closest approach this comet will make to Earth since the Stone Age. Astronomers have calculated that this comet, which has been named C/2022 E3 ZTF, was last visible from Earth approximately 50,000 years ago.
Additionally, this comet glows with a greenish hue due to a relatively high concentration of diatomic carbon (C2), which emits an emerald-colored glow as it is broken down by sunlight. This phenomenon can be observed in a number of other comets as well, but rarely do these types of comets approach Earth closely enough for the green color to be seen.
These types of cosmological events pop up in the news cycle every so often, it seems. An eclipse, a meteor shower, or an object usually unobservable with the naked eye coming into view catches the fancy of reporters, who then reach out to astronomers, the life's work of whom goes completely unnoticed by most of the public 99 percent of the time, for comment.
We then learn (or re-learn) what said object or phenomenon is, agree that it's interesting, then forget all about it and move on with our busy lives.
Which is more than fair enough. It's especially the case in a city like Shanghai, where the bright lights and glitz and glamor of the city produce the unfortunate negative side effect of light pollution for night-sky watchers and enthusiasts, making objects in space much more difficult to spot.
In centuries past, though, this certainly was not the case. In the era before megacities, and particularly before the invention of electric lighting, the cosmos was much more visible and prominent in the night sky and a totally unavoidable topic of conversation and speculation. Given that the scientific understanding of what the saw of the people of that time was essentially zero, myriad myths, tales, and legends arose from varying interpretations of the cosmos around the globe.
The ancient Babylonians were the first to catalog the constellations and map the stars systematically, dividing the night sky into 12 sections of equal size. This idea was reimagined and expanded in many societies over the following centuries and still lives on in the form of the zodiac we all know today.
China too, of course, has its own ancient stories and mythology related to the stars. Perhaps the most famous of these is the tale of the cowherd and the weaver girl. These characters represent the prominent stars Altair and Vega, respectively, and in the fable, the two share a romance that is interrupted by the Queen Mother, who to this day only allows them to meet once per year, on the seventh day of the seventh lunar month. This day is now known as Qixi, or China's equivalent of Valentine's Day.
Of course, the stars weren't merely a source of mythology and fables in centuries past. They functioned as a vital navigation system as well before the advent of the technologies we enjoy today. Perhaps fittingly, the open sea might be the only place on the planet where one might be able to observe the galaxy and the stars to a degree approaching that of ancient times.
Comets, particularly, have been a source of fear, wonder, and perceived bad omens for centuries. Ancient figures like William the Conqueror and Genghis Khan were said to have carried out their conquests after observing comets piercing through the cosmos, seeing them as signs from the heavens portending victory.
In more recent times, countless loony doomsday preachers have forecast the end of days due to the approaching of comets such as Halley's in 1910 and 1986 and Hale-Bopp in 1997.
Fortunately for us all, these prophecies of Armageddon have hit at an exactly zero percent rate.
At any rate, in Shanghai today, only a precious few celestial objects can be observed with the naked eye on a clear night. Our planetary neighbors Jupiter, Venus, and Mars can be seen. Although many casual observers might mistake them for stars, they are in fact the brighter of the planets that orbit the Sun alongside us. Though Venus is generally the brightest of these from our perspective, last autumn, Jupiter outshone it easily and could be spotted clearly without visual aid.
I have, on particularly clear nights and after allowing for time for my eyes to adjust to the sky's darkness, been able to spot a few actual stars. One night in 2021 while on a rooftop observing a lunar eclipse, I found that a few other stars were visible, and using the Xingtu (star map) app, I learned that I'd caught a glimpse of the star Deneb as well as the aforementioned Altair and Vega. So I can vouch for the fact that, given the right timing and the right conditions, some stars can be seen from here in the city.
So if you have a pair of binoculars and perhaps find yourself a little ways outside of the city center on a clear night this month, have a gander upward and see if you can spot the green comet, our visitor from the Solar System's outermost reaches. It appears as a small, blurry spot of light near Polaris, the North Star, so if you can find that, the comet will be in its vicinity. Have a look, because if you miss it, the green streak won't be back for another 50,000 years!