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arctic: arctic: [14] Etymologically, the Arctic is the region of the ‘bear’. Nothing to do with polar bears, though. The characteristic constellations of the northern hemisphere are the ‘Little Bear’ (Latin Ursa Minor), which contains the northern celestial pole, and the Plough, otherwise known as the ‘Great Bear’ (Latin Ursa Major). The perception that they resemble a bear (Greek arktos) goes back to ancient times, and the Greeks used the derived adjective arktikos, literally ‘relating to bears’, to denote ‘northern’.

By the time this reached English, via Latin ar(c)ticus and Old French artique, it was being applied specifically to the northern polar regions. (The original English spelling, reflecting the French form, was artic. The more etymologically ‘correct’ arctic came in in the 17th century, but uncertain spellers are still apt to regress to artic.) Antarctic [14] for the corresponding southern polar region likewise comes ultimately from Greek (antarktikos, with the prefix anti- ‘opposite’). Arcturus [14], the name of a very bright star in the constellation Boötes, means literally ‘bear watcher’ or ‘bear guardian’ (Greek Arktouros), a reference to the fact that the tail of the Great Bear points towards it.
Arctic Circle: 1550s, in reference to a celestial circle, a line around the sky which, in any location, bounds the stars which are ever-visible from that latitude (in the Northern Hemisphere, this is focused on the celestial north pole); the concept goes back to the ancient Greeks, for whom this set of constellations included most prominently the two bears (arktoi), hence the name for the circle (see arctic). Of Earth, the circle 66 degrees 32 minutes north of the equator, marking the southern extremity of the polar day, it is recorded from 1620s.
mazel tov: 1862, from modern Hebrew mazzal tob "good luck," from Hebrew mazzaloth (plural) "constellations."
sidereal (adj.): also siderial, 1630s, "star-like;" 1640s, "of or pertaining to the stars," earlier sideral (1590s), from French sidereal (16c.), from Latin sidereus "starry, astral, of the constellations," from sidus (genitive sideris) "star, group of stars, constellation," probably from PIE root *sweid- "to shine" (cognates: Lithuanian svidus "shining, bright"). Sidereal time is measured by the apparent diurnal motion of the fixed stars. The sidereal day begins and ends with the passage of the vernal equinox over the meridian and is about four minutes shorter than the solar day, measured by the passage of the sun over the meridian.
Ursa Major: "One of the largest and most prominent northern constellations (the Great Bear). The seven brightest stars form a familiar formation variously called the Plough, Big Dipper, or Charles’s Wain, and include the Pointers", Latin, from the story in Greek mythology that the nymph Callisto was turned into a bear and placed as a constellation in the heavens by Zeus.