Nigerian skies, in 2017 – Part 6
You can take part in this ancient tradition. Just plan an outing for any evening, between April 16th and 25th, preferably on the 21st, 22nd or 23rd.
Indeed, IMO’s Alastair McBeath describes the Lyrids as “a medium strength shower [ZHR 18] that usually produces good rates for three nights centered on the [22nd] maximum”.
Ejecta from comet C/1861 G1 (Thatcher), he notes, ablate in Earth’s atmosphere at some 48 km per second, creating bright meteors and occasionally a fireball.
Thatcher is non-periodic. But Halley—the most famous of all the comets—rounds the Sun every 75-76 years, strewing friable shower material in its path.
Starting around April 19th, Earth collides with clumps of this debris, triggering a succession of luminous atmospheric events, known generically as the Aquariid Shower Complex.
The complex consists of major and minor showers which, Wikipedia reports, encompasses “Eta,” “Kappa,” “North Iota,” “Southern Delta,” “South Iota” and “Tau” Aquariids.
Unlike their iconic progenitor, these are hardly household appellations. But fun is where you find it. And two of the Aquariids are designated “Class I” displays, based on intensity.
One of these is Eta, which Australian savants Jonti Hunter and Tanya Hill describe as “the stronger of two annual showers” produced when Earth passes through Halley’s debris.
Writing in The Conversation, they affix April 19th thru May 28th as active dates for this exhibition (ZHR 50), with its “forecasted maximum” falling on May 6th.
The Aquariids are named for Eta Aquarii—a white, naked-eye subgiant in Aquarius constellation, where the radiant appears to lie. An interesting footnote, from retired University of Illinois astronomer, Jim Kaler, is that Eta will cross the celestial equator in 2022, to become a Northern Hemisphere star.
But this won’t affect the showers, whose intensity is greatest in Southern skies, with possibly 30 swift meteors per hour also accruing to equatorial viewers.
The second major Aquariid display, is Delta Aquariids. Delta is actually part of a sub-complex, within the broad Aquariid system. Sources differ, on the units. Wikipedia enumerates a seven-cluster complex, while Hunter and Hill mention only three—The Southern Delta Aquariids, Piscis Austrinids and Alpha Capricornids.
“These three showers, combined,” they advise, “favour observers in the southern hemisphere, though they can also be observed from northern latitudes”.
It is probable, that the displays on Wikipedia’s more detailed list, are subsumed under one of the three. Moving beyond minutia, the complex has a ZHR of 35 and confers its aesthetic largesse on patient observers from early-July to Mid-August, reaching a three-day plateau July 28th-30th.
Vying with Delta Aquariids and associates, and eventually overpowering them, is the Perseids—one of the Big Three, and justly idolized, among meteor initiates, as a star-performer.
“The best known of all meteor showers,” Reddy writes, “the Perseids never fail to put on a good show and… are usually widely observed”. Perseids is visible in northern skies, from July 17th to August 24th. Nevertheless, Nigerians can reap a share of its visual harvest, especially during the shower’s prolific 9th -thru-13th peak.
At ZHR 150, this scion of comet (109P Swift-Tuttle) promises 80 or so actual sighting per hour, for mid-latitude viewers, and possibly as many as 50 in clear Nigerian skies.
The Society for Popular Astronomy (U.K.) warns that lunar lighting may be a problem. But don’t be disheartened. Not even a 21-day-old Moon, can outshine the Perseids shower!