- scarp
- line of cliffs produced by faulting or erosion.
- Schiaparelli, Giovanni
Virginio 1835-1910
- Italian astronomer who in 1877 first observed the
"canals" on Mars. He believed
that the features he observed included straight
lines that joined in a complicated pattern. He
called these lines 'canali', which means
'channels'. However, the Italian word was
mistranslated into the English word 'canals'.
That, combined with the suspicious straightness
of the lines, bespoke of artificial structures,
and this created a furor. Speculations concerning
the possibility of intelligent life on Mars
sprang up in the popular press. Even astronomers
felt the pull of that dramatic possibility.
Foremost among these was Percival
Lowell, who carried matters far beyond
Schiaparelli.
- scopulus
- lobate or irregular scarp.
- semimajor axis
- the semimajor axis of an ellipse (e.g. a
planetary orbit) is 1/2 the length of the major
axis which is a segment of a line passing thru
the foci of the ellipse with endpoints on the
ellipse itself. The semimajor axis of a planetary
orbit is also the average distance from the
planet to its primary. The periapsis and apoapsis distances can
be calculated from the semimajor axis and the eccentricity by rp =
a(1-e) and ra = a(1+e).
- Shakespeare, William
1564-1616
- English playwright and poet; wrote some good
skits.
- shepherd satellite
- (or 'shepherd moon') a satellite which constrains
the extent of a planetary ring through
gravitational forces. (See Pandora for a nice
image.)
- sidereal
- of, relating to, or concerned with the stars.
Sidereal rotation is that measured with respect
to the stars rather than with respect to the Sun
or the primary of a satellite.
- sidereal month
- The average period of revolution of the moon
around the earth in reference to a fixed star,
equal to 27 days, 7 hours, 43 minutes in units of
mean solar time.
- silicate
- a compound containing silicon and oxygen (e.g.
olivine)
- sinus
- literally "bay"; really a small plain
- solar cycle
- the approximately 11-year quasi-periodic
variation in frequency or number of solar active
events.
- solar nebula
- the cloud of gas and dust that began to collapse
about 5 billion years ago to form the solar
system.
- solar wind
- a tenuous flow of gas and energetic charged
particles, mostly protons and electrons -- plasma
-- which stream from the Sun; typical solar wind
velocities are near 350 kilometers per second.
- speed of light
- = 299,792,458 meters/second (186,000
miles/second). Einstein's
Theory of Relativity
implies that nothing can go faster than the speed
of light; Scotty and Geordi know better.
- spicules
- grass-like patterns of gas seen in the solar
atmosphere.
- stellar classification
- Stars given a designation consisting of a letter
and a number according to the nature of their
spectral lines which corresponds roughly to
surface temperature. The classes are: O, B, A, F,
G, K, and M; O stars are the hottest; M the
coolest. The numbers are simply subdivisions of
the major classes. The classes are oddly
sequenced because they were assigned long ago
before we understood their relationship to
temperature. O and B stars are rare but very
bright; M stars are numerous but dim. The Sun is
designated G2.
- sublime (or
sublimate)
- to change directly from a solid to a gas without
becoming liquid
- sulcus
- subparallel furrows and ridges.
- sunspot
- an area seen as a dark spot on the photosphere of the
Sun; sunspots are concentrations of magnetic
flux, typically occurring in bipolar clusters or
groups; they appear dark because they are cooler
than the surrounding photosphere.
- superior planets
- the planets Mars,
Jupiter, Saturn, Uranus, Neptune
and Pluto are
called superior planets because their orbits are
farther from the Sun than Earth's orbit.
- synchronous orbit radius
- the orbital radius at which the satellite's
orbital period is equal to the rotational period
of the planet. A synchronous satellite with an
orbital inclination
of zero (same plane as the planet's equator)
stays fixed in the sky from the perspective of an
observer on the planet's surface (such orbits are
commonly used for communications satellites).
- synchronous rotation
- said of a satellite if the period of its rotation
about its axis is the same as the period of its
orbit around its primary. This implies that the
satellite always keeps the same hemisphere facing
its primary (e.g. the Moon). It also
implies that one hemisphere (the leading
hemisphere) always faces in the direction of the
satellite's motion while the other (trailing) one
always faces backward. Most of the satellites in
the solar system rotate synchronously.
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