When Comet ATLAS (C/2019 Y4) was discovered on December 28, 2019 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) it was a very dim magnitude +20 object however, once it’s orbit was calculated it was initially tagged as a “comet to watch” in 2020. Comets are fickle objects, and while the message was sent and received by the astronomical community, most astronomers (professional and amateur alike) knew the standard caveat that precedes such news. Comets are like cats. Predicting their behavior is a risky business.
Best described as dirty snowballs with highly elliptical orbits they typically blossom as they get closer to their parent star. This blossoming occurs when solar radiation causes the nucleus of the comet to sublimate forming a coma or shroud of gas and dust to form around the speeding comet. The closer the comet gets to the Sun usually the more material is spewed, and the classic “comet tail” forms trailing the icy body and always pointing away or perpendicular from the Sun.