Nigerian skies, in 2017 – Part 4
Meteor showers are celestial light shows, in which “shooting stars” occur in larger numbers, and more frequently, than at other times. The showers begin, peak and end on specific dates.
There are at least 10 major displays annually (depending on whose classification you accept) and several minor ones. I will list them in part “(5)”: But let’s do the backgrounding, first.
A “meteor” is simply the light (and sometimes the sound), generated as small particles of space debris burn up during their rapid atmospheric passage—typically, at 11 to 72 km per second.
As it ablates, the particle heats up (from friction) and ionizes, both itself and the surrounding air—leaving in its wake, a streak of light that is often visible for less than a second.
Much heralded exceptions, are massive, boulder-like bodies: Which arrive, quite literally, in a blaze of visual glory that can last for several seconds.
I’ll brief you about “fireballs,” later. Perhaps your most pulsating question now, is “Where do these intrusive masses—these ‘meteoroids,’ as astronomers say—come from?”
Well, there are trillions-upon-trillions of rocky and iron meteoroids careering around the Sun, in countless orbital scenarios—ranging, in size, from a meter across to microscopic.
Among them, are asteroid flakes, flying helter-skelter from the site of some primordial impact. And, also, pieces of Mars and the Moon, plus pebbles and grains, sewn in the paths of subliming comets.
(FYI: The National Museum, at Kaduna, houses an historic piece of Mars that landed near Katsina, in 1962.)
Most of the major—and many of the minor—showers are visible in Nigerian skies. Yet indigenes seldom look up at night. So, the munificence of the firmament eludes them!
Nevertheless, accidental sightings do happen. These normally carry ominous connotations, which find expression in the folk-belief that “A Big Man is going to die!”.
Such “Big Man” signs, are usually “sporadic” meteors—not associated with a major or minor shower. (“Meteor” is the scientific term for “shooting star”.) Sporadic flashes can appear, on any clear night.
The time and patience you invest in a prolonged watch, will eventually payoff. But for a given duration, sporadic meteors are potluck: “You pays yo’ money,” so to speak, “and takes yo’ chances”.
Reaffirming this, is Robert Lunsford, who apparently works with the American Meteor Society (AMS) as well as the International Meteor Organization (IMO).
Sporadic flashes, he writes, “are usually… random occurrences not associated with any particular meteor shower. In fact, there are areas of the sky which continually produce [such] activity…”
Astronomers have plotted six dispersed directions, within the inner solar system, from which random apparitions originate.
By contrast, all shower-meteors are the discarded residue of melting comets or (in at least one case) asteroids. Earth plows through the rings of debris, crisscrossing its orbit, on the same dates every year.
Hence showers are, in general terms, predictable, whereas sporadic meteors are not. What is more, astronomers can even forecast the intensity of a meteor shower, months in advance.
The intensity of a major or minor exhibition, notes an AMS posting, is expressed as the Zenith Hourly Rate (ZHR), which “standardizes the shower rate to optimum observing conditions”.
In Nigeria, “optimum” viewing conditions, would be a pitch-dark night, under a perfectly clear sky, somewhere in the rural North or the mountainous Middle Belt.
The truth is, though, ZHR refers to an idealized standard, rather like a “black body” in physics. Because of this, even the best performing showers, rarely measure up to their ZHR billings.