At some time or another, we have all seen animals in clouds and faces on trees. The human brain is adept at detecting patterns and shapes, even when they aren't really there. It is no surprise, therefore, that people the world over look at the random scattering of stars in the night sky and assign them into arbitrary groupings which, supposedly, form pictures of mythic creatures and legendary heroes. We know these star-groups as constellations, from the Latin con- (a form of cum) "with, together", and stella, "star". The ancients assumed the stars to be fixed to a vast dome and that the stars of each constellation were, thus, physically adjacent to one another.

Some clusters of stars actually are close and one such is the Pleiades in the constellation Taurus. The traditional English name for this cluster is the seven sisters but the stars actually number in the thousands. The Japanese name for this cluster is subaru, by the way. 

Most of the fixed stars are within our own "Milky Way" galaxy while others, which look like stars to the unaided eye, are entire galaxies in the distant depths of space. The word galaxy, which  was initially applied only to the Milky Way, derives from the Greek galaxios "milk".  The stem of this word becomes galact- in certain cases, which shows its relationship to lactose, a sugar found in milk, and more surprisingly, to lettuce (from Latin lactuca) a plant with a milky, white sap.

Some ancient stargazers (in Sumeria, Central America, and China) noticed that certain "stars" wander around the sky from one constellation to another. [The Mayan and Chinese constellations are totally different from ours, by the way.]  The Greeks called them planetai, their word for "wanderer", which is why we call these "stars" planets.

The early astronomers also observed that the sun, moon and planets move only within a narrow band of the sky. This is because the orbits of the planets and all their various moons are all (pretty much) in the same plane. The result is that, occasionally, one planet can block our view of another. Astronomers call this phenomenon occultation, from the Latin occultare "hide". Such events generally occur without general consternation and alarm, the exception being when our moon occults the sun. This is called an eclipse (from Greek ekleipein "to fail to appear") and, as a consequence, the orbital plane is also known as the ecliptic plane.

As they orbit the sun, the planets appear to pass through a succession of twelve  constellations. Because six of the twelve (seven if you count the amphibian goat-fish) represented animals, the Greeks knew this cycle of constellations as zodion kuklos, "the circle of animals". This became zodiacus in Latin and zodiac in English. The Greek word zodion is a diminutive of zoon, "animal", and is related to zoe, "life" and, hence, to our zoology (the science of animal life), and zoo (an abbreviation of zoological gardens). More obscurely, there is zodiographer - not a horoscope columnist but "one who writes about animals". 

Horoscope is a borrowing from the Greek 'oroskopos, literally "one who watches the time". Speaking of which, it's time for bed.

TRIVIA ANSWER: The one constellation whose stars are physically adjacent to one another is the Pleiades. 

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