Accumulation of dust
and gas into larger bodies such as stars, planets and moons.
- Adams, John Couch
English astronomer and
mathematician who, at the age of 24, was the first person to
predict the position of a planetary mass beyond
But, unfortunately, Adams did not publish his prediction.
confirmed the existance of
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).
A dark or light marking
on the surface of an object that may not be a geological or
- 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
having the form of a
bow; curved; arc-shaped
- Arago, Dominique
Francois Jean 1786 -
French astronomer and
physicist and Director of the Paris Observatory, who discovered
the phenomenon of the production of magnetism by rotation
Danish astronomer who
with the first observations of
After receiving its predicted position from
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. (90k
(also "planetoid") a
rocky object orbiting the Sun; smaller than a planet, larger
than a meteoroid
asteroids are assigned
a serial number when they are discovered. It has no particular
meaning except that asteroid N+1 was discovered after asteroid
1.03 kg/cm2 = 14.7 pounds per square inch, standard atmospheric
pressure at sea level on Earth.
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.
= 1.02 kg/cm2 = 100 kilopascal = 14.5 lbs/square inch.
- Barnard, Edward
and Barnard's star, the second-nearest star system to the Sun.
The local name for Mars
in Edgar Rice Burroughs' SF books.
- Bode, Johann Elert
known for the bogus "Bode's
Law" which attempts to explain
the sizes of the planetary orbits.
that produces a sonic boom
- Bond, William Cranch
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 studied
discovered its moon
- Brahe, Tycho
(a.k.a Tyge Ottesen)
Danish astronomer whose accurate astronomical observations
formed the basis for Johannes
laws of planetary motion. (141k
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
(a.k.a. Jean Dominique)
Italian-born French astronomer and first director of the
Observatory in Paris;
discoverer of four of
and the major gap in its rings. (13k
chain of craters.
distinctive area of
the lower level of the
atmosphere between the
small hills or knobs.
the dust and gas
surrounding an active
icy object orbiting the Sun; smaller than a planet
the legislative branch
of the US Government; has proven to be a much more hostile
environment for scientific spacecraft than the vastness of
driven by large temperature gradients; the transfer of heat by
this automatic circulation.
Polish astronomer who
theory that the Earth and other planets revolve around the Sun.
This was highly controversial at the time as the
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 heliocentic
idea was first put forth by Aristarcus of Samos in the 3rd
century BC, a fact known to Copernicus but long ignored.) (470k
the uppermost level of
atmosphere, characterized by low densities and high temperatures
(> 1.0E+06° K).
a special telescope
which blocks light from the disk of the
order to study the faint solar atmosphere.
- cosmic ray
an extremely energetic
(relativistic) charged particle.
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
the apparent change in
wavelength of sound or light caused by the motion of the source,
observer or both. (see
large reptiles that
lived in the Mesozoic Era from 230 to 65 million years ago; most
probably wiped out by the impact of a large
rotation or orbital
motion in a counterclockwise direction when viewed from the
north pole of the primary (i.e. in the same sense to most
satellites); the opposite of
The north pole is the one on the same side of the
as the Earth's north pole. (The word "prograde" is sometimes
used to mean "direct" in this sense.)
the eccentricity of an
ellipse (planetary orbit) is the ratio of the distance between
the focii and the major axis. Equivalently the eccentricity is
(ra-rp)/(ra+rp) where ra is the
distance and rp is the
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
- Einstein, Albert
physicist; developed the Special and General
Theories of Relativity
which along with Quantum Mechanics is the foundation of modern
speed of light)
oval. That the orbits
of the planets are ellipses, not circles, was first discovered
based on the careful observations by
= 1e-10 kilowatts.
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
"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.
a strand of cool gas
suspended over the
by magnetic fields, which appears dark as seen against the
filament on the
the Sun seen in emission against the dark sky is called a
a narrow opening or
crack of considerable length and depth.
a sudden eruption of
energy on the solar
lasting minutes to hours, from which radiation and particles are
long, narrow, shallow
- Franklin, Benjamin
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 the environment. First advanced by British biologist
James Lovelock in 1969.
- Galle, Johann
German astronomer who,
with Heinrich Louis
made the first observation of
based on calculations by
Though Galle was the first to observe Neptune, its discovery is
usually credited to
(who made an earlier calculation) and Le Verrier.
four largest moons:
discovered independently by
(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
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
theory. In reaction to Galileo, the Church declared it heresy to
teach that the Earth moved and imprisoned him. The Church clung
to this position for 350 years; Galileo was formally exonerated
in 1992. (16k
(See also the Galileo exhibit at
Institute and Museum of History of
Science, Florence ITALY and
The Galileo Project
a round or elongated
spot of light in the sky at a point 180 degrees from the Sun.
Also called counterglow.
- George III
King of Great Britain
and Ireland (1760-1820). His government's policies fed American
colonial discontent, leading to revolution in 1776.
- geosynchronous orbit
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 planet's surface.
a pattern of small
cells seen on the surface of the
caused by the convective motions of the hot solar gas.
increase in temperature
caused when incoming solar radiation is passed but outgoing
thermal radiation is blocked by the atmosphere (carbon dioxide
is the major factor). Very important on
largely absent on
- Hale, George Ellery
American astronomer who
founded the Yerkes, Mt. Wilson and Palomar observatories. (72k
- Hall, Asaph
American astronomer who
discovered the two moons of
- Halley, Edmond
English astronomer who
laws of motion to historical comet data and predicted correctly
the reappearance of the
which now bears his name. (12k
the point at which the
meets the interstellar medium or solar wind from other stars.
the space within the
boundary of the heliopause containing the
- Herschel, Sir
British astronomer who
and cataloged more than 800 double stars and 2,500 nebulae. (365k
- Hubble, Edwin
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
Dutch physicist and
astronomer who first described the nature of
rings (1655) and discovered its moon
also pioneered the use of the pendulum in clocks. (7k
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 inclination of a moon's orbit is the angle between the plane
of its orbit and the plane of its primary's equator.
A Renaissance Catholic
court instituted to seek out and prosecute heretics.
- inferior planets
called inferior planets because their orbits are closer to the
- interplanetary magnetic field (IMF)
the magnetic field
carried with the
a region of charged
particles in a planet's upper atmosphere; the part of the
atmosphere beginning at an altitude of about 25 miles and
extending outward 250 miles or more.
- Kelvin (K)
0 Kelvin is absolute
zero; water melts at 273 K (= 0° C = 32° F); water boils at 373
K (= 100° C = 212° F). (developed by William
- Kepler, Johannes
German astronomer and
mathematician. Considered a founder of modern astronomy, he
formulated the famous
of planetary motion. They comprise a quantitative formulation of
theory that the planets revolve around the Sun. (16k
= 1000 grams = 2.2
pounds, the mass of a
- kilometer (km)
- Kowal, Charles
object 2060 Chiron (aka 95 P/Chiron).
- Kuiper, Gerard
astronomer best known for his study of the surface of the
found an atmosphere on
(Dr.Kuiper was solidly Americanized; his name is pronounced to
rhyme with "viper.") (22k
- Lagrange, Joseph
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 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. Such bodies
are sometimes refered to as
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. (see
- Lassell, William
A successful brewer before turning to astronomy. (22k
- Le Verrier,
Urbain Jean Joseph
whose prediction of the position of an undiscovered planet (Neptune)
that caused perturbations in the orbit of
was the first to be confirmed (by
made a similar but unpublished prediction some months earlier.
an instrument similar
to radar that operates at visible wavelengths.
the outer edge of the
disk of a
- lumière zodicale
a faint glow from light
scattered off of
along the plane of the
= 9.46053e12 km (=
5,880,000,000,000 miles = 63,239 AU); the distance traveled by
light in a year.
= 1000 cm3 = 1.06 US
- Lowell, Percival
American astronomer. He
founded the Lowell Observatory in Arizona (1894), where his
him to believe that the linear markings (first noted by
on the surface were "canals" and therefore that the planet was
inhabited by intelligent beings. His successors later discovered
the region of space in
which a planet's magnetic field dominates that of the
the portion of a
planetary magnetosphere which is pushed in the direction of the
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
- Marius, Simon
(a.k.a. Mayr) German
astronomer who gave
moons their names. He and
both claimed to have discovered them in 1610 and likely did so
independently. They become involved in a dispute over priority.
Marius was also the first to observe the Andromeda Nebula with a
telescope and one of the first to observe
used by astrophysicists
to refer to all elements except hydrogen and helium, as in: "the
universe is composed of hydrogen, helium and traces of metals".
(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
extra-terrestrial origin found on Earth
rocky object orbiting the Sun; smaller than an asteroid
1/1000 of a
Standard sea-level pressure is about 1013 millibars.
- minor planets
the official term used
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
English cleric and
scientist; discovered the classical laws of
the bit with the apple is probably apocryphal. (10k
- Nicholson, Seth
also did important work on
- 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
famous equivalence E=mc2. This is the source of the
energy therefore ultimately of (almost) all energy on Earth.
really a large circular plain
a planetary surface
that has been modified little since its formation typically
featuring large numbers of impact craters (compare
- Oort, Jan Hendrik
Dutch astronomer made
major contributions to knowledge of the structure and rotation
of our galaxy. More or less as a sideline, Oort studied
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
bits of which are occasionally hurled into the solar system as
shaped like an egg
really a small plain
AU = 3.26
scalloped, complex edge.
literally, "dim light";
the outer filamentary region of a
the point in its orbit
where a planet is closest to the Sun. when refering to objects
orbiting the Earth the term perigee is used; the term periapsis
is used for orbits around other bodies. (opposite of
- Perrine, Charles
astronomer who discovered
to cause a planet or
satellite to deviate from a theoretically regular orbital motion
the visible surface of
are observed in the photosphere.
bright regions seen in
William Henry 1858-1938
His photographs of Mars, among the earliest obtained, provided a
basis for his opposition to
observations of supposed canals on Mars. Discovered
plateau or high plain.
- Pope, Alexander
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
which appears bright when seen at the edge of the Sun against
the blackness of space.
Ptolemaeus) Alexandrian astronomer, mathematician, and
geographer who based his astronomy on the belief that all
heavenly bodies revolve around the Earth. (10k
- red giant
a star that has low
surface temperature and a diameter that is large relative to the
describes the motions of bodies in strong gravitational fields
or near the
speed of light
mechanics. All experiments done to date agree with relativity's
predictions to a high degree of accuracy. (Curiously,
in 1921 not specifically for Relativity but rather for his 1905
work on the photoelectric effect and "services to Theoretical
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
rotation or orbital
motion in a clockwise direction when viewed from the north pole
of the primary (i.e. in the opposite sense to most satellites);
the opposite of
The north pole is the one on the same side of the ecliptic as
the Earth's north pole.
- 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 parallel
- 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 structural strength. The
Roche limit is calculated with the equation
where p' is the density
of the planet, p is the density of the moon, and R is the radius
of the planet. (more)
line of cliffs produced
by faulting or erosion.
Schiaparelli, Giovanni Virginio
Italian astronomer who
in 1877 first observed the "canals" on
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
who carried matters far beyond Schiaparelli.
lobate or irregular
- 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
distances can be calculated from the semimajor axis and the
by rp = a(1-e) and ra = a(1+e).
- Shakespeare, William
English playwright and
poet; wrote some
- lune berger
(or 'shepherd moon') a
satellite which constrains the extent of a planetary ring
through gravitational forces. (See
for a nice image.)
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.
a compound containing
silicon and oxygen (e.g. olivine)
literally "bay"; really
a small plain
- solar cycle
11-year quasi-periodic variation in frequency or number of
- solar nebula
the cloud of gas and
began to collapse about 5 billion years ago to
- solar wind
a tenuous flow of gas
and energetic charged particles, mostly protons and electrons --
plasma -- which stream from the
typical solar wind velocities are near 350 kilometers per
- speed of light
meters/second (186,000 miles/second).
implies that nothing can go faster than the speed of light;
Scotty and Geordi know better.
grass-like patterns of
gas seen in the
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
to change directly from
a solid to a gas without becoming liquid
subparallel furrows and
an area seen as a dark
spot on the
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
called superior planets because their orbits are farther from
- synchronous orbit
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
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).
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
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.
acting on a planet's crust.
the dividing line
between the illuminated and the unilluminated part of the moon's
or a planet's
extensive land mass.
tile; terrain formed of
small domical mountain
- Thomson, William
aka Lord Kelvin,
British physicist who developed the
scale of temperature. Also supervised the laying of a
trans-Atlantic cable. (10k
- tidal heating
frictional heating of a
satellite's interior due to flexure caused by the gravitational
pull of its parent planet and possibly neighboring satellites.
- Tombaugh, Clyde
(also "Trekker") a
devotee of the science fiction program Star Trek.
an object orbiting in
points of another (larger) object. This name derives from a
generalization of the names of two of the largest
Lagrange points: 624 Hektor and 911 Agamemmnon.
are also sometimes called Trojans.
the dark central region
- unité astronomique
average distance from the
Sun. 1 AU
is a long way -- at 100 miles per hour (160 kph) it would take
over 100 years to go 1 AU.
sinuous valley (plural:
- Van Allen, James
American physicist who
radiation belts (that now bear his name) with an instrument
aboard the first successful American satellite, Explorer 1.
- Verne, Jules
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 and methane.
- white dwarf
a whitish star of high
surface temperature and low intrinsic brightness with a mass
approximately equal to that of a
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
young; the surfaces of