DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

S
Sagittarius A* Strong radio source located
in Sagittarius and apparently located at the center
of the Galaxy at RA 17 h 45 m .6 , dec −28 ◦ 56 ′
(at galactic longitude 0, latitude 0). Measurements
of stellar velocity profiles near the center
of the object indicate the presence of an object
of mass approximately 2.6×10 6 M⊙ in a sphere
of radius 0.15 pc. This implies the existence of
a massive black hole at the center of our galaxy,
at about 8 kpc.
saline contraction coefficient Coefficientβ
expressing the relative change of density due
to the change in salinity at constant potential
temperature and pressure p; i.e., β =
ρ −1 (∂ρ/∂S),p. β does not vary strongly for
fresh-water to marine saline to hypersaline water
(∼ 0.7 to 0.85). For actual values see Algorithms
for computation of fundamental properties
of seawater, UNESCO Tech. Pap. Mar. Sci.,
44, 53 pp.
salinity The total fractional amount of dissolved
material in seawater defined as the total
amount of solid materials in grams contained in
1 kg of seawater when all the carbonate has been
converted to oxide, the bromine and iodine replaced
by chlorine, and all organic matter completely
oxidized. The average salinity of seawater
varies from about 3.5 to 3.7% by weight.
There is an observed constant ratio of chlorinity
to salinity: salinity in parts per thousand =
(1.80655) (chlorinity in parts per thousand). See
chlorinity.
salinity inversion See density inversion.
saltation Eolian or fluvial transport of small
material by the bouncing of that material along a
surface. Saltation is particularly effective for the
transport of sand-sized material (1/16 to 2 mm
in diameter).
salt fingering See double diffusion.
Satellite Laser Ranging (SLR)
salt wedge A horizontal tongue of saline water
located beneath a layer of fresh water within
an estuary.
sand budget A description of all of the sand
within a littoral system and a description of
where it is going.
sand bypassing A process, either natural or
as a result of man’s activities, whereby sand is
transported past a tidal inlet or entrance channel
and reaches the beach on the other side.
sand spit A long, thin deposit of sand, deposited
by longshore sediment transport. Typically
located at the downdrift end of an island.
sand trap A trench dredged to capture sand.
Such a trap is often used to facilitate sand bypassing.
The trap is dredged near the updrift side
of a channel or harbor entrance, captures sand,
and the sand is later dredged out and placed on
the downdrift beach.
Sargasso Sea Area in the north Atlantic
Ocean between the West Indies and the Azores,
at about 30 N lat. This relatively still sea
is bounded by the North Atlantic, Canary,
North Equatorial, and Antilles Currents, and the
Gulf Stream. Named for the large amount of
free floating seaweed (Sargassum) accumulated
there.
saros 223 synodic (lunar) months = 19
eclipse years (almost exactly), about 18 years
11 days, a period of time over which the relative
orientation of the moon and the sun repeat, so
that lunar eclipses recur in similar patterns.
satellite altimetry A space-based ranging
technique, which usually analyzes laser or radar
pulses reflected off of the surface of a planet.
When combined with precise orbit determination
of the satellite, these rangings can be used
to determine ocean, ice, and land surface topography.
See also TOPEX/POSEIDON.
Satellite Laser Ranging (SLR) Determination
of the distance between an artificial satellite
with reflecting prisms and an observation station
on the Earth’s surface, by radiating laser beam
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