An Etymological Dictionary of Astronomy and Astrophysics
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1) Detached, disconnected, disjoined.
2) To set apart; disconnect; dissociate.

→ separation.

Star formation rate per unit → mass. More specifically, the → star formation rate in a galaxy divided by the → stellar mass of the galaxy. Observations of galaxies over a wide range of → redshifts suggest that the slope of the SFR-M_* relation is about unity, which implies that their sSFR does not depend strongly on stellar mass. Specific star formation rates increase out to z ~ 2 and are constant, or perhaps slowly increasing, from z = 2 out to z = 6, though with a large scatter, sSFR ~ 2-10 Gyr^-1 (Lehnert et al., 2015, A&A 577, A112, and references therein).

→ specific; → star; → formation; → rate.

The rate at which a molecular cloud or a galaxy is currently converting gas into stars. It is given by the ratio of the number of stars to the star formation time-scale.

→ star formation; → rate.

To oscillate with a continuing periodic change relative to a fixed reference point or state of equilibrium. → oscillate.

From L. vibratus, p.p. of vibrare "to move quickly to and fro, shake" (cf. Lith. wyburiu "to wag the tail," Dan. vippe, Du. wippen "to swing," O.E. wipan "to wipe").

Šividan "to vibrate, move to and fro, to tremble," related to šodan, šow- "to go; to become;" Av. šiyav-, š(ii)auu- "to move, go," šiyavati "goes," šyaoθna- "activity; action; doing, working;" O.Pers. šiyav- "to go forth, set," ašiyavam "I set forth;" Skt. cyu- "to move to and fro, shake about; to stir," cyávate "stirs himself, goes;" Gk. kinein "to move;" Goth. haitan "call, be called;" O.E. hatan "command, call;" PIE base *kei- "to move to and fro."

A crater about 70 km in diameter in Western Australia, considered to be the oldest recognized → meteorite impact structure on Earth. A precise age of 2 229 ± 5 million years is derived from shocked zircon and monazite crystals in the rocks. The age coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits. Numerical impact simulations indicate that a 70 km size crater created by the impact in a continental glacier could release between 8.7 × 10¹³ to 5.0 × 10¹⁵ kg of H₂O vapor instantaneously into the atmosphere. These results provide new estimates of impact-produced H₂O vapor abundances for models investigating termination of the Paleoproterozoic glaciations, and highlight the possible role of impact cratering in modifying Earth's → climate (Erikson, T.M. et al., 2020, Nature communications, 21 January).

The Yarrabubba structure is located on the Yilgarn Craton in Western Australia (lat. 27° 11'S, long. 118° 50'E), approximately 100 km southeast of the township of Meekatharra; → crater.

The number of → meteors expected to be seen under ideal conditions if the → radiant of the → meteoroid stream is at the → zenith of the → observer.

→ zenith; → hour; → rate.