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prettygoodwordsidereal (sai-DEER-ee-uhl) - adj., of, relating to, or determined by the stars; (astron.) (of time) measured by the apparent motion of the fixed stars.
The sidereal day is slightly shorter than the solar day, because as the earth rotates it also moves around the sun, so to get the sun in the same place it has to rotate further than to get a fixed star to the same place -- thus the progression of stars through the seasons. Sidereal time is irrelevant to most of us who aren't astronomers, but vitally important to them -- more important, probably, than knowing when the sun goes down and comes back up. First used in this spelling in 1634, alteration of earlier sideral, borrowed in 1594 from French sidereal, from Latin sīdereus, starry, astral, from sīdus, star, constellation, probably from the PIE root *sweid-, to shine.
---L.
The sidereal day is slightly shorter than the solar day, because as the earth rotates it also moves around the sun, so to get the sun in the same place it has to rotate further than to get a fixed star to the same place -- thus the progression of stars through the seasons. Sidereal time is irrelevant to most of us who aren't astronomers, but vitally important to them -- more important, probably, than knowing when the sun goes down and comes back up. First used in this spelling in 1634, alteration of earlier sideral, borrowed in 1594 from French sidereal, from Latin sīdereus, starry, astral, from sīdus, star, constellation, probably from the PIE root *sweid-, to shine.
---L.
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Date: 2010-10-21 04:38 am (UTC)no subject
Date: 2010-10-21 05:20 pm (UTC)(Man, the animation on that icon is disturbingly fast. Makin' me dizzy.)
---L.