Comet-ary

Would you care to comment on a comet?
For it's true that there is a lot to say.
About these long haired apparitions,
As through the night they play.

Icy and eccentric, though elliptical in their outgassing passing,
As we observe them, swerve then, as they orbit about the sun.
Periodically visiting, though some much more often than others,
Cousins from the Kuiper Belt, live not so far away, that is to say,
Beyond Neptune is comparatively right on the doorstep,
If we consider those from the Oort Cloud can be halfway to the next star.
When impelled by the gravitational perturbations of some star as it meanders by,
Or else the ripples of the galactic tide, begat by the milky way,
An Oort comet may begin an orbit that could take several million years.

How can we not mention Astronomer Royal Edmond Halley?
He calculated the periodicity of his subsequently eponymous comet,
Seeing, as a matter of fact, its several places in history,
Actually the very first to have its orbit and period calculated.
And this was no small matter, this short-period comet.
For it was the first object other than a planet, that was proven to orbit the sun.
And its predicted return, in seventeen five eight,
(though sadly too late, for the, by then, also late, Professor Halley),
Was a very successful test of the Newtonian physics, published at his expense.

Comet in a coma sublime as it comes closer to the corona this time.
Fred Whipple's dirty snowballs, of dust and ice and ammonia,
Carbons di and mon, d'oxide and also methane, about a rocky core.
Or else the deep fried ice cream, crystalline organic compounds all
Wrapped around a colder and less dense interior ice.
Low albedos, reflecting some tiny percentage of the light that falls upon them.
Amongst the least reflective objects in the solar system, comets absorb heat,
Driving their outgassing, streams of dust and gas forming the coma,
A huge thin atmosphere, which chased by the solar wind, and
Bowing to the radiation pressure, may form a tail.

Some we have visited, for example 67P/Churyumov–Gerasimenko
The Rosetta spacecraft went to orbit and its lander Philae bounced about a bit,
But softly landed. Thus became the first such to do so on a comet nucleus.
Though aiming at area J, now Agilkia, it had fallen beneath the shadow of a cliff..
Intermittently indicating it was still operative, Philae transmitted to Rosetta,
Sent images and data before its batteries died, alas, laid, in the shade,
Unable to recharge, and sabotaged by circumstance.