Short answers, pulled from the story.
The solid core of a comet is known as the nucleus. It measures from a few hundred meters to tens of kilometers across and consists of loose collections of ice, dust, and small rocky particles.
Fred Whipple described comets as dirty snowballs in 1950. Later observations revealed some are actually icy dirtballs with higher dust content.
Halley's Comet reflects about four percent of incoming sunlight while asphalt reflects seven percent. This dark material absorbs heat that drives outgassing processes.
Short-period comets originate in the Kuiper belt or its scattered disc beyond Neptune. Long-period comets come from the Oort cloud which extends from outside the Kuiper belt to halfway to the nearest star.
A German farmer named Georg Palitzsch actually saw it first on December 25th and 26th of 1758. French mathematicians Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute refined this prediction before his observation.
Rosetta orbited Comet Churyumov-Gerasimenko and landed Philae on its surface on the 12th of November 2014. This was the first time a spacecraft ever landed on such an object.