- Accumulation of dust and gas into larger bodies such as stars, planets and moons.
- Adams, John Couch 1819-1892
- English astronomer and mathematician who, at the age of 24, was
the first person to predict the position of a planetary mass beyond
Uranus. But, unfortunately, Adams did not publish
his prediction. Galle
confirmed the existence of Neptune
based on independent calculations done by
- the ratio of the amount of light reflected by an object and the amount
of incident light; a measure of the reflectivity or intrinsic brightness
of an object (a white, perfectly reflecting surface would have an albedo of
1.0; a black perfectly absorbing surface would have an albedo of 0.0).
- albedo feature
- A dark or light marking on the surface of an object
that may not be a geological or topographical feature.
- antipodal point
- the point that is directly on the opposite side of the planet
- the point in its orbit where a planet is farthest from the Sun;
when refering to objects orbiting the Earth the term apogee
is used; the term apoapsis is used for orbits around other bodies.
(opposite of perihelion)
- having the form of a bow; curved; arc-shaped
- Arago, Dominique François Jean 1786 - 1853
- French astronomer and physicist and Director of the
Paris Observatory, who
discovered the phenomenon of the production of magnetism by rotation
- d'Arrest, Heinrich Louis
- Danish astronomer who
assisted Galle with the first observations of
After receiving its predicted position from Le Verrier,
Galle and d'Arrest began searching.
With Galle at the eyepiece and d'Arrest reading the chart, they scanned the
sky and checked that each star seen was actually on the chart. Just a few
minutes after their search began, d'Arrest cried out, "That star is not on
the map!" and earned his place in the history books.
- (also "planetoid")
a medium-sized rocky object orbiting the Sun;
smaller than a planet, larger than a meteoroid
- asteroid number
- asteroids are assigned a serial number when they are discovered. It has no
particular meaning except that asteroid N+1 was discovered after asteroid N.
(see appendix 5)
- astronomical unit (AU)
- = 149,597,870.691 km; the average distance from the
1 AU is a long way -- at 100 miles per hour (160 kph) it would take over
100 years to go 1 AU.
- = 1.013 bars = 1.03 kg/cm^2 = 14.7 pounds per square inch,
standard atmospheric pressure at sea level on Earth.
- (Latin for "dawn") a glow in a planet's ionosphere caused by the interaction between the
planet's magnetic field and charged particles from the Sun
- aurora borealis
- the "Northern Lights"; caused by the interaction between the
the Earth's magnetic field and the upper atmosphere. A similar effect
happens in the southern hemisphere
where it is known as the aurora australis.
- = 0.987 atmosphere = 1.02 kg/cm^2 = 100 kilopascal =
14.5 lbs/square inch.
- Barnard, Edward Emerson 1857-1923
- American astronomer; discovered Jupiter's
and Barnard's star, the second-nearest star system to the Sun.
- The local name for Mars in Edgar Rice Burroughs' SF books.
- I use the American version of "billion" which means 1,000,000,000 (1e9); not the
British version which means 1e12.
- Bode, Johann Elert 1747-1826
- German astronomer, known for the bogus
which attempts to
explain the sizes of the planetary orbits.
- a fireball that produces a sonic boom
- Bond, William Cranch 1789-1859
- One of the earliest American astronomers of note;
rose from poverty and overcame a lack of formal education to become
the first director of the Harvard College Observatory where he
and (with Lassell)
discovered its moon Hyperion.
- Brahe, Tycho 1546-1601
- (a.k.a Tyge Ottesen)
Danish astronomer whose accurate astronomical observations formed
the basis for Johannes Kepler's laws of planetary motion.
The Noble Dane: Images of Tycho Brahe, from the Museum of the History of Science in Oxford)
- brown dwarf
- An object between 0.013 and 0.080 solar masses (13 to 80 Jupiter-masses):
too small for normal nuclear fusion but big enough to fuse deuterium.
Brown dwarfs are larger than planets but smaller than stars.
- crater formed by an explosion or collapse of a volcanic vent.
- a compound containing carbon and oxygen (i.e. calcium carbonate a.k.a. limestone).
- Cassini, Giovanni Domenico 1625-1712
- (a.k.a. Jean Dominique) Italian-born French astronomer and first director
of the Royal Observatory in Paris;
discoverer of four of
Saturn's moons (Tethys,
and Iapetus) and the major division in its rings.
- chain of craters.
- Hollow, irregular depression.
- distinctive area of broken terrain.
- Christy, James W.
- discoverer of Pluto's moon Charon (331k jpg (Jim is the seated figure at left))
- the lower level of the solar atmosphere
between the photosphere
and the corona
- small hills or knobs.
- the dust and gas surrounding an active comet's nucleus
- a medium-sized icy object orbiting the Sun;
smaller than a planet
- An inferior planet is said to be "in inferior conjunction" when it is directly between the Earth and the Sun. It is "in superior conjunction" when it is on the opposite side of the Sun from the Earth. A superior planet is "in conjunction" when it is on the opposite side of the Sun from the Earth. A superior planet obviously cannot have an inferior conjunction. When the Earth is at inferior conjunction with respect to an observer on a superior planet we say that planet is "in opposition" from Earth's perspective.
. (nice diagram)
- the legislative branch of the US Government; has proven to be a much more
hostile environment for scientific spacecraft than the vastness of space.
- fluid circulation driven by temperature gradients in the presence of gravity; the
transfer of heat by this mechanism.
- Copernicus, Nicolaus 1473-1543
- Polish astronomer who advanced the heliocentric
theory that the Earth and other planets
revolve around the Sun.
This was highly controversial at the time as
the Ptolemaic view of the universe, which was the
prevailing theory for over 1000 years, was deeply ingrained in the
prevailing philosophy and religion.
(It should be noted, however, that the heliocentric idea was first put forth by
Aristarcus of Samos in the 3rd century BC, a fact known to Copernicus but long
( 12k gif;
- ovoid-shaped feature.
- the uppermost level of the solar atmosphere,
characterized by low densities and high temperatures (> 1.0E+06 K).
- a special instrument which blocks light from the
disk of the Sun in order to
study the faint solar atmosphere.
- cosmic ray
- an extremely energetic (relativistic) charged particle.
- bowl-shaped depression formed by the impact of a
depression around the orifice of a volcano.
- measured in grams per cubic centimeter (or kilograms per liter); the density
of water is 1.0; iron is 7.9; lead is 11.3.
- literally "bad stars"; particularly apt in reference to a major asteroid impact.
- the visible surface of the Sun (or any heavenly body) projected
against the sky.
- doppler effect
- (Christian Doppler 1803-1853) the apparent change in wavelength of sound or light caused by
the motion of the source, observer or both.
- large animals that lived in the
Mesozoic Era from 230 to 65 million years ago; most probably wiped
out by the impact of a large
asteroid or comet.
- rotation or orbital motion in a counterclockwise direction when viewed looking down
from above the north pole of the primary (i.e. in the same sense to most satellites);
the opposite of retrograde.
The north pole is the one on the same side of the
ecliptic as the Earth's north pole.
(The word "prograde" is sometimes used to mean "direct" in this sense.)
- dwarf planet
- A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite. Currently there are three objects: Pluto, Ceres and Eris officially designated as dwarf planets. (See planet.)
- the eccentricity of an ellipse (planetary orbit) is the ratio
of the distance between the foci and the major axis. Equivalently the eccentricity
is (ra-rp)/(ra+rp) where ra is the apoapsis distance
and rp is the periapsis distance.
- effusive eruption
- a relative quiet volcanic eruption which puts out basaltic lava
that moves at about the speed one walks; the lava is fluid in nature;
the eruptions at the Kilauea volcano on the island of Hawaii are effusive
- Einstein, Albert 1879-1955
- German-American physicist; developed the Special and General
Theories of Relativity which along with Quantum Mechanics
is the foundation of modern physics. (See fusion,
speed of light)
- oval. That the orbits of the planets are ellipses, not circles, was first
discovered by Johannes Kepler based on the
careful observations by Tycho Brahe.
- = 1e-10 kilowatts.
- explosive eruption
- a dramatic volcanic eruption which throws debris high into the
air for hundreds of miles; lava is low in silicate; can be very
dangerous for people near by; an example is Mount St. Helens in 1980
- exponential notation
- "1.23e4" means "1.23 times 10 to the fourth power" or 12,300; "5.67e-8" means
"5.67 divided by 10 to the eighth power" or 0.0000000567.
- bright spot.
- pancake-like structure
- a strand of cool gas suspended over the
photosphere by magnetic fields, which
appears dark as seen against the disk
of the Sun;
a filament on the limb of the Sun seen in
emission against the dark sky is called a
- a meteor brighter than magnitude -3
- a narrow opening or crack of considerable length and depth.
- a sudden eruption of energy on the solar disk
lasting minutes to hours, from which radiation and particles are emitted.
- cuspate (pointed) linear feature.
- flow terrain.
- long, narrow, shallow depression.
- Franklin, Benjamin 1706-1790
- American public official, writer, and scientist. Played a major part
in the American Revolution and helped draft the Constitution.
His numerous scientific and practical innovations include the lightning
rod, bifocal spectacles, and a stove.
- Gaia Hypothesis
- named for the Greek Earth goddess Gaea, holds that the Earth
as a whole should be
regarded as a living organism and that biological processes stabilize
First advanced by British biologist James Lovelock in 1969.
- Galle, Johann Gottfried 1812-1910
- German astronomer who,
with Heinrich Louis d'Arrest,
made the first observation of
on calculations by Le Verrier.
Though Galle was the first to observe Neptune,
its discovery is usually credited to
Adams (who made an
earlier calculation) and Le Verrier.
- Galilean Moons
- Jupiter's four largest moons:
Callisto; discovered independently by
Galileo and Marius.
(Galileo proposed that they be named the Medicean stars, in honor
of his patron Cosimo II de Medici; the present names are due to Marius)
- Galileo Galilei 1564-1642
- Italian astronomer and physicist. The first to use a telescope to study the
stars. Discoverer of the first moons of an extraterrestrial body (see above).
Galileo was an outspoken supporter of Copernicus's
heliocentric theory. In reaction to Galileo,
the Church declared it heresy to teach that the Earth moved and silenced
him. The Church clung to this position for 350 years; Galileo was not formally
exonerated until 1992.
(See also the Galileo exhibit at Institute and Museum of History of Science, Florence ITALY;
The Galileo Project from Rice and APOD 980913)
- a round or elongated spot of light in the sky at a point 180 degrees from
the Sun. Also called counterglow.
- George III 1738-1820
- King of Great Britain and Ireland (1760-1820). His government's policies fed
American colonial discontent, leading to revolution in 1776.
- geosynchronous orbit
- a direct, circular,
low inclination orbit in which the satellite's
orbital velocity is matched to the rotational velocity of the planet;
a spacecraft appears to hang motionless above one position of the
- a pattern of small cells seen on the surface of
the Sun caused by
the convective motions of the hot solar gas.
- greenhouse effect
- increase in temperature caused when incoming solar radiation is passed but
outgoing thermal radiation is blocked by the atmosphere (carbon dioxide and water
vapor are the major factors).
Very important on Venus and
Earth but very weak on Mars.
- Hale, George Ellery 1868-1938
- American astronomer who founded the Yerkes, Mt. Wilson and Palomar observatories.
- Hall, Asaph 1829-1907
- American astronomer who discovered the two moons of Mars,
Deimos and Phobos.
- Halley, Edmond 1656-1742
- English astronomer who applied Newton's laws of
motion to historical comet data and predicted correctly
the reappearance of the comet
which now bears his name.
(12k jpg; more)
- Sun-centered; see Copernicus,
- the point at which the solar wind
meets the interstellar medium or solar wind from other stars.
- the space within the boundary of the heliopause containing the
Sun and solar system.
- Herschel, Sir William 1738-1822
- British astronomer who discovered Uranus and
cataloged more than 800 double stars and 2,500 nebulae.
- Hubble, Edwin Powell 1889-1953
- American astronomer whose observations proved that galaxies are
"island universes", not nebulae inside our own galaxy.
His greatest discovery was the linear relationship
between a galaxy's distance and the speed with which it is moving.
The Hubble Space Telescope is named in
his honor. (133k html/gif;
- Huygens, Christiaan 1629-1695
- Dutch physicist and astronomer who first described the nature of
Saturn's rings (1655) and discovered
its moon Titan;
also pioneered the use of the pendulum in clocks.
- used by planetary scientists to refer to water, methane, and ammonia which
usually occur as solids in the outer solar system.
- the inclination of a planet's orbit is
the angle between the plane of its orbit and the
the inclination of a moon's orbit is
the angle between the plane of its orbit and the plane of its primary's equator.
- Inquisition, The
- A Renaissance Catholic court instituted to seek out and prosecute heretics.
- inferior planets
- the planets Mercury
and Venus are called inferior planets because their
orbits are closer to the Sun
than is Earth's orbit.
(The other planets are called "superior" planets.)
- interplanetary magnetic field (IMF)
- the magnetic field carried with the solar wind.
- a region of charged particles in a planet's upper atmosphere;
the part of the Earth's
atmosphere beginning at an altitude of about
25 miles and extending outward 250 miles or more.
- Keeler, James E. 1857-1900
- American astrophysicist, probable
discoverer of the dark narrow gap in the outer part
of the A ring of Saturn, and the second director of
Keeler was (probably accidentally) cheated of
his rightful fame when the A ring gap became known as "Encke's Division".
Encke had earlier seen a broad, poor contrast feature in the A-ring (now called
the "Encke Minimum" by some amateurs) which is quite different
from the sharp, distinct gap that Keeler recorded on the very first night of
observing with the Lick 36-inch refractor.
Images from Voyager and Cassini show a much smaller gap near the very outer edge
of the A ring which has been named the Keeler Gap. Of course, Keeler never saw it.
On the other hand, the "Encke" gap which was seen by Keeler may have been seen
even earlier by Francesco De Vico,
William Lassell and/or the Rev. William R. Dawes.
- Kelvin (K)
- 0 Kelvin is absolute zero;
H2O melts at 273 K (= 0° C = 32° F);
H2O boils at 373 K (= 100° C = 212° F).
(developed by William Thomson).
- Kepler, Johannes 1571-1630
- German astronomer and mathematician. Considered a founder of modern
astronomy. Using the positional data carefully
amassed by Tycho Brahe,
Kepler formulated the famous
of planetary motion.
They comprise a quantitative formulation of
Copernicus's theory that
the planets revolve around the Sun.
- kilogram (kg)
- = 1000 grams = 2.2 pounds, the mass of a liter of water.
- kilometer (km)
- = 1000 meters = 0.62 miles.
- Kowal, Charles T. 1940-
- American astronomer; discovered Leda
and the comet-like object 2060 Chiron
(aka 95 P/Chiron).
- Kuiper, Gerard 1905-1973
- Dutch-born American astronomer best known for his study of the surface of the
Moon; discovered Miranda
found an atmosphere on Titan.
(Dr.Kuiper was solidly Americanized; his name is pronounced to rhyme with "viper.")
(a short bio)
- intersecting valley complex.
- Lagrange, Joseph Louis 1736-1813
(originally Italian, Giuseppe Luigi Lagrangia; born in Turin,
moved to Paris and became a French citizen)
mathematician and astronomer; made a number of contributions to the
study of celestial mechanics.
- Lagrange points
Lagrange showed that three bodies can lie at the apexes of an equilateral
triangle which rotates in its plane.
If one of the bodies is sufficiently massive compared with the other two,
then the triangular configuration is apparently stable.
Bodies at such points are sometimes referred to as Trojans.
The leading apex of the triangle is known as the leading Lagrange
point or L4; the trailing apex is the trailing Lagrange point or L5.
Collinear with the two large bodies are the L1, L2 and L3 unstable equilibrium points which can sometimes be useful places for spacecraft, eg SOHO.
- Lassell, William 1799-1880
- British astronomer, discovered Neptune's
largest satellite, Triton and (with
A successful brewer before turning to astronomy.
- Le Verrier, Urbain Jean Joseph 1811-1877
- French mathematician whose prediction of the position of an undiscovered
that caused perturbations in the orbit of
Uranus was the first to be confirmed (by
Galle) though Adams had made
a similar but unpublished prediction some months earlier.
- an instrument similar to radar that operates at visible wavelengths.
- the outer edge of the apparent disk of a celestial body
- = 9.46053e12 km (= 5,880,000,000,000 miles = 63,239 AU);
the distance traveled by light in a year.
- elongate marking.
- = 1000 cm3 = 1.06 US quarts
- Lowell, Percival 1855-1916.
- American astronomer. He founded the Lowell Observatory in Arizona (1894),
of Mars led him to believe
that the linear markings
(first noted by Schiaparelli)
on the surface were "canals" and therefore
that the planet was inhabited by intelligent beings.
His successors later discovered Pluto.
- lunar month
- The average time between successive new or full moons, equal to 29 days 12 hours 44 minutes. Also called synodic month.
- dark spot.
- the region of space in which a planet's magnetic field dominates that of the
- the portion of a planetary magnetosphere which is pushed away from the Sun
by the solar wind.
- The degree of brightness of a celestial body designated on a numerical scale,
on which the brightest star has magnitude -1.4 and the faintest visible star
has magnitude 6, with the scale rule such that a decrease
of one unit represents an increase in apparent brightness
by a factor of 2.512. Also called apparent magnitude.
- literally "sea" (a very bad misnomer, still in use for historical reasons);
really a large circular plain (plural: "maria")
- Marius, Simon 1573-1624
- (a.k.a. Mayr) German astronomer who gave Jupiter's
their names. He and Galileo both
claimed to have discovered them in 1610 and likely did so independently.
Marius was also the
first to observe the Andromeda Nebula with a telescope and one of the
first to observe sunspots.
- mesa, flat-topped elevation.
- used by astrophysicists to refer to all
except hydrogen and helium,
as in: "the universe is composed of hydrogen, helium and traces
of metals". (Note: this is quite different from the usual chemistry definition.)
- (also "shooting star" or "falling star") a bright streak of light in the sky
caused by the entry into Earth's atmosphere of a meteoroid
or a small icy particle. Very large, bright ones are called
fireballs and bolides
- a rock of extra-terrestrial origin found on Earth
- a small rocky object orbiting the Sun;
smaller than an asteroid
- 1/1000 of a bar. Standard sea-level pressure is about 1013
- minor planets
- the official term used for asteroids.
- mountain (plural: montes)
- Neujmin, Grigoriy N.
- Ukrainian astronomer; discovered the asteroid
- a fundamental particle supposedly produced in massive numbers by the nuclear
reactions in stars. They are very hard to detect since the vast majority of
them pass completely through the Earth without interacting.
- Newton, Isaac 1642-1727
- English cleric and scientist; discovered the classical laws of
the bit with the apple is probably apocryphal.
- Nicholson, Seth Barnes 1891-1963
- American astronomer; discovered
Sinope; also did important work
- nuclear fusion
- a nuclear process whereby several small nuclei are combined to
make a larger one whose mass is slightly smaller than the sum of the small
ones. The difference in mass is converted to energy by
equivalence E=mc2. This is the source of the Sun's
energy therefore ultimately of (almost) all energy on Earth.
- literally "ocean"; really a large circular plain
- a planetary surface that has been modified little since its formation
typically featuring large numbers of impact craters
- Oort, Jan Hendrik 1900-1992
- Dutch astronomer made major contributions to knowledge of the structure and
rotation of our galaxy. More or less as a sideline, Oort studied
comets as well.
The result of this work was a theory, now widely accepted, that the
Sun is surrounded by a distant cloud of comet-stuff, now called the
Oort cloud, bits of which are occasionally hurled into
the solar system as comets.
- A superior planet is said to be "in opposition" when it is directly on the opposite side of the Earth from the Sun. This is generally the closest it comes to the Earth and the time at which it is most easily visible. (nice diagram)
- shaped like an egg
- literally "swamp"; really a small plain
- = 206265 AU = 3.26 light year
- shallow crater; scalloped, complex edge.
- literally, "dim light"; the outer filamentary region
of a sunspot.
- the point in its orbit where a planet is closest to the Sun.
when referring to objects orbiting the Earth the term perigee
is used; the term periapsis is used for orbits around other bodies.
(opposite of aphelion)
- Perrine, Charles Dillon 1867-1951
- Argentine-American astronomer who discovered
- to cause a planet or satellite to deviate from a
theoretically regular orbital motion .
- the visible surface of the Sun;
and faculae are observed in the photosphere.
- bright regions seen in the solar
- Piazzi, Giuseppe 1746-1826
- Astronomer, born in Ponte di Valtellina, Italy. He
became a Theatine monk, professor of theology in Rome (1779), and professor
of mathematics at the Academy of Palermo (1780). He set up an observatory
at Palermo in 1789, published a star catalog (1803, 1814) and discovered
and named the first minor planet, Ceres.
- Pickering, William Henry 1858-1938
- American astronomer. His photographs of Mars, among the earliest obtained,
provided a basis for his opposition to
Lowell's observations of supposed canals on Mars.
- The recently adopted IAU resolution states that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:
So by this official definition there are exactly eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto, Ceres and Eris (aka 2003 UB313) are "dwarf planets" with a potentially large number of additional objects falling into this category in the near future.
- A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
- A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
- All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".
- low plain.
- plateau or high plain.
- Pope, Alexander 1688-1744
- English writer best remembered for his satirical mock-epic poems
The Rape of the Lock and The Dunciad.
- a strand of relatively cool gas in the solar
corona which appears
bright when seen at the edge of the Sun against the blackness of space.
- cape; headland
- Ptolemy 87-150
- (aka Claudius Ptolemaeus) Alexandrian astronomer, mathematician,
and geographer who based his
astronomy on the belief that all heavenly bodies revolve around the Earth.
- red giant
- a star that has low surface temperature and a diameter that is
large relative to the Sun.
- Relativity, Theory of
- more accurately describes the motions of bodies in strong gravitational
fields or near the speed of light than
newtonian mechanics. All
experiments done to date agree with relativity's predictions to a high degree
of accuracy. (Curiously, Einstein received the
in 1921 not specifically for Relativity but rather for his 1905
work on the photoelectric effect and "services to Theoretical Physics".)
(see Spacetime Wrinkles, an excellent WWW site from NCSA)
- the amount of small detail visible in an image;
low resolution shows only large features,
high resolution shows many small details
- A state in which one orbiting object is subject to periodic
gravitational perturbations by another.
- reticular (net-like) pattern
- rotation or orbital motion in a clockwise direction when viewed
from above the north pole of the primary
(i.e. in the opposite sense to most satellites);
the opposite of direct.
The north pole is the one on the same side of the ecliptic as the Earth's
- rift valley
- an elongated valley formed by the depression of a block of the
planet's crust between two faults or groups of faults of approximately
- Roche limit
- the closest a fluid body can orbit to its primary without being
pulled apart by tidal forces. A solid body may
survive within the Roche limit if the tidal forces do not exceed its
The Roche limit is calculated with the equation
RL = 2.456*R*(p'/p)^(1/3)
where p' is the density of the planet, p is the density of the moon,
and R is the radius of the planet.
(here's the math)
- 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
- 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
- shepherd satellite
- (or 'shepherd moon') a satellite which constrains the extent of a planetary ring
through gravitational forces. (See Pandora for a
- 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.
- a compound containing silicon and oxygen (e.g. olivine)
- 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
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
solar wind velocities are near 350 kilometers per second.
- speed of light
- = 299,792,458 meters/second (186,000 miles/second).
of Relativity implies that nothing can go faster
than the speed of light; Scotty and Geordi know better.
- 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
- subparallel furrows and ridges.
- an area seen as a dark spot on the
photosphere of the Sun;
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,
Neptune and Pluto
are called superior planets because their
orbits are farther from the Sun
than Earth's orbit.
(Mercury and Venus are called "inferior" planets.)
- 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
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
- 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.
- deformation forces acting on a planet's crust.
- the dividing line between the illuminated and the unilluminated
part of the moon's or a planet's disk.
- extensive land mass.
- tile; terrain formed of polygonal pattern
- small domical mountain or hill.
- Thomson, William 1824-1907
- aka Lord Kelvin, British physicist who developed the
of temperature. Also supervised the laying of a trans-Atlantic cable.
- tidal heating
- frictional heating of a satellite's interior due to flexure
caused by the gravitational pull of its parent planet and possibly
- Tombaugh, Clyde 1906-1997
- American astronomer; discovered Pluto.
- (also "Trekker") a devotee of the science fiction program Star Trek.
- an object orbiting in the Lagrange points of
another (larger) object. This name derives from a generalization of the
some of the largest asteroids in
Lagrange points: 588 Achilles, 624 Hektor, and 911 Agamemnon.
Telesto are also sometimes called Trojans.
- the dark central region of a sunspot.
- dunes (literally 'waves').
- sinuous valley (plural: valles)
- Van Allen, James A.
- American physicist who discovered the Earth's
radiation belts (that now bear
his name) with an instrument aboard the first successful
American satellite, Explorer 1.
- widespread lowlands.
- Verne, Jules 1828-1905
- French writer who is considered the founder of modern science fiction.
His novels include "Journey to the Center of the Earth" and "From the Earth
to the Moon".
- As a noun, this refers to substances that are gases at ordinary temperatures.
In astronomy it includes hydrogen, helium, water, ammonia, carbon dioxide
- white dwarf
- a whitish star of high surface temperature and low intrinsic
brightness with a mass approximately equal to
that of a Sun but
with a density many times larger.
- When used to describe a planetary surface "young" means that the visible
features are of relatively recent origin, i.e. that older features have
been destroyed (e.g. by erosion or lava flows). Young surfaces exhibit few
impact craters and are typically varied and complex.
In contrast an "old" surface
is one that has changed relatively little over geologic time. The surfaces of
and Io are young; the
surfaces of Mercury,
and most other solid bodies in our solar system are old.
- zodiacal light
- a faint glow from light scattered off of
interplanetary dust along the plane of the
- People from LANL
- Biographies of Mathematicians, including some who were also astronomers and/or physicists (includes many portraits).
- Institute and Museum of History of Science, Florence ITALY (Biographies in the Galileo exhibit)
- Astronomical People (with images)
- People from the University of Michigan's wonderful "Windows to the Universe", includes many pictures