Hesperus
2 of the 6 encyclopedias on this shelf carry an entry for Hesperus. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
hes'per-us, or Hesper, the ancient name for the planet Venus when it appeared as the evening star. In mythology, Hesperus was, according to Hesiod, the son of Astraeus and Eos. According to other accounts, he was a son of Atlas and brother of the Hesperides. Still others make him brother of Atlas and father of the Hesperides. See Hesperides Hessian (hesh'an) Fly, a well known insect pest. It is a small fly. It is allied to the gnat and the midge. The adult female is about one-tenth of an inch in length. The body is brown with blackish upper parts. It has dusky gray wings, surrounded with fringe. Two generations are raised in a year. In September the fly lays its eggs in growing winter wheat. The maggots hatch in from four to fourteen days. The fall generation lives over winter in the wheat field and is ready for work in the spring. It matures and lays eggs again in May, this time in the joints between the leaf sheaths and the stem. The May generation is the one that does the damage. The maggots turn into pupae, known from their appearance as flaxseed, and work their way into the joints of the wheat stem. The stalk loses strength and the head falls over worthless. Of the various cereals, barley and rye are least subject to attacks of this insect. The wheat raiser dreads the Hessian fly more than he does the chinch bug. Directly and indirectly, it is said to cause the American farmer an annual loss of $50,000,000. In damp seasons certain parasites attach themselves to the Hessian flies and all but exterminate them. For a year or two the farmer's fields are comparatively free from the pest. The name was given by the American colonists in a belief, no doubt unfounded, that the fly was brought to America in the baggage of the Hessian soldiers, who were employed by England. See Chinch-Bug
Collier's New Encyclopedia (1921)
the Greek name for Venus as the evening star. Hence the Alexandrian grammarians called Italy, and sometimes all western Europe, Hesperia, "The Western land."
What Has Changed in the Last Century
Both entries are still correct: Venus at its evening apparitions was Hesperus to the Greeks, Phosphorus or Lucifer when it rose before the sun, and the genealogies Aiton's lists from Hesiod and other writers remain exactly as muddled in the sources today. What has changed is the planet rather than the name. When Collier's wrote this in 1921 Venus was a cloud-covered mystery often imagined as warm and swampy; Soviet Venera probes, beginning with the first surface landing in 1970, found a crushing carbon-dioxide atmosphere about ninety times Earth's pressure and surface temperatures near 460 degrees Celsius. The pair of names has also had a second career in philosophy, where "Hesperus is Phosphorus" is the standard textbook example of an identity statement that is true but not obvious.
Written for this edition, 2026.