Hastings' Dictionary of the New Testament 
The Dioscuri were the sons of Leda and Zeus, Castor being mortal and Pollux immortal. They were famed for many exploits, and at length, in a battle against the sons of Aphareus, Castor was slain by Idas. Pollux besought Zeus that he too might die. According to one fable the Father of the Gods granted Castor life on condition that the brothers should alternately spend a day in Hades, but another states that their love was rewarded by Zeus, who placed them together among the stars as the Gemini. They were regarded as the patrons of athletic contests, Castor presiding over the equestrian events, Pollux being the god of boxing (Κάστορά δʼ ἱππόδαμον καὶ πὺξ ἀγαθὸν Πολυδεύκεα [Hom. Il . iii. 237]). Their worship was very strictly observed among the Dorian peoples, and they were also held in special reverence at Rome, as they were popularly supposed to have fought on the side of the Common wealth at the battle of Lake Regillus and to have carried the news of victory to the city (Dion. Hal. Ant. Rom . vi. 13), It is worthy of note that they were specially held in honour in the district of Cyrenaica near Alexandria ( schol . Pindar, Pyth . v. 6).
The ships of the ancients carried two figures as a rule, one being the figure-head (παράσημον, insigne ), after which the ship was named (Virgil, aen . v. 116, x. 166, 188, 209), and the other in the stern. The latter was the tutela or image of the divine being under whose guardianship the vessel was supposed to sail. The Dioscuri were regarded as the guardian deities of sailors, and Horace speaks of ‘the brothers of Helen, the beaming stars,’ as shining propitiously on those at sea ( Odes , i. iii. 2, xii 25; cf. Catullus, iv. 27; Euripides, Helena , 1662-5).
F. W. Worsley.
Hastings' Dictionary of the Bible 
DIOSCURI (RVm [Note: Revised Version margin.] ), or The Twin Brothers (RV [Note: Revised Version.] ), or Castor and Pollux (AV [Note: Authorized Version.] ). The sign or figurehead of the Alexandrian ship in which St. Paul sailed from Malta ( Acts 28:11 ), perhaps one of those employed to bring corn to Rome. The Twins ( Gemini ) were the protectors of sailors; in mythology they were sons of Zeus and Leda, and were placed in the sky as a constellation for their brotherly love.
A. J. Maclean.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
( Διόσκουροι . i.e., Jove's boys, "Castor and Pollux," Acts 28:11), the twin sons of Jupiter by Leda (Homer, Hymn, 17; Hygin. Fab . 77; according to Homer, Odyss . 11:297, the sons of Leda and Tyndareus). They were chiefly invoked by the Greek and Roman sailors as tutelary deities of mariners, and also worshipped by propitiatory offerings (Theocritus, Id. 22:17; Catull. lxviii. 65; Lucian, Deor. dial. 26:2). In the heavens they were twin stars, regarded as auspicious (comp. Σωτῆρες , Homer, Hymn , 33:6; Elian, Var. Inst . 1:30; "lucidum sidus," Diodor. Sic. 4:43; Ovid, Fasti, 5:720). They were sometimes thought to appear in a delivering flame at the masthead during storms (Plutarch, Placit. Philos. 2:18). Their image formed the "figure-head" of the Alexandrian vessel (giving name to it) in which Paul sailed from Melita to Rome ( Acts 18:11). Compare (See Ship). See Scheffer, De Nilit. Navali Vett . page 372 sq.; Ensched, De tutelis et insignib. Nav . (L. B. 1771); Hasmeus, De navib. Alexand. Apostolum In Ital. Deferentibus (Brem. 1716); Kunz, De Vexillo Navis Alex . (Jen. 1734). Comp. (See Castor (And Pollux).)
International Standard Bible Encyclopedia 
dı̄ - os´kū - rı̄ ( Διόσκουροι , Dióscouroi ; in Acts 28:11 , the King James Version Castor and Pollux , the Revised Version (British and American) The Twin Brothers; in margin, "Dioscuri"): The sign of the ship on which Paul sailed from Melita to Syracuse and Rhegium. The Dioscuri (i.e. sons of Zeus), Castor and Pollux, are the two chief stars in the constellation of the Twins. Some 4,000 years bc they served as pointers to mark the beginning of the new year by setting together with the first new moon of springtime. The constellation of the Twins was supposed to be especially favorable to sailors, hence, ships were often placed under the protection of the twin gods.
The Nuttall Encyclopedia 
Twin sons of Zeus, Castor and Pollux, a stalwart pair of youths, of the Doric stock, great the former as a horse-breaker and the latter as a boxer; were worshipped at Sparta as guardians of the State, and pre-eminently as patrons of gymnastics; protected the hearth, led the army in war, and were the convoy of the traveller by land and the voyager by sea, which as constellations they are still held to be.