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
Le Verrier.
(4k jpg)
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).
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)
Danish astronomer who
assisted Galle with the first observations of
Neptune.
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.
(90k jpg)
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)
= 149,597,870.691 km; the average distance from the
Earth to
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.
the "Northern Lights"; caused by the interaction between the
solar wind,
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.
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 Saturn
and (with Lassell)
discovered its moon Hyperion.
(a.k.a Tyge Ottesen)
Danish astronomer whose accurate astronomical observations formed
the basis for Johannes Kepler's laws of planetary motion.
(141k jpg;
38k jpg;
more;
The Noble Dane: Images of Tycho Brahe, from the Museum of the History of Science in Oxford)
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.
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)
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
ignored.)
(470k html/gif;
12k gif;
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more)
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.)
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.
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
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.
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
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
prominence.
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.
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.
German astronomer who,
with Heinrich Louis d'Arrest,
made the first observation of
Neptune based
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.
Jupiter's four largest moons:
Io,
Europa,
Ganymede and
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)
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.
(16k gif;
136k jpg)
(See also the Galileo exhibit at Institute and Museum of History of Science, Florence ITALY;
The Galileo Project from Rice and APOD 980913)
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
planet's surface.
granulation
a pattern of small cells seen on the surface of
the Sun 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 and water
vapor are the major factors).
Very important on Venus and
Earth but very weak on Mars.
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)
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;
60k gif;
bio material)
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.
(7k jpg;
more)
the inclination of a planet's orbit is
the angle between the plane of its orbit and the
ecliptic;
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
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.)
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.
American astrophysicist, probable
discoverer of the dark narrow gap in the outer part
of the A ring of Saturn, and the second director of
Lick Observatory.
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") 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.
On the other hand, the gap may have been seen even earlier by Francesco De Vico, William Lassell and the Rev. William R. Dawes.
German astronomer and mathematician. Considered a founder of modern
astronomy. Using the positional data carefully
amassed by Tycho Brahe,
Kepler formulated the famous
three laws
of planetary motion.
They comprise a quantitative formulation of
Copernicus's theory that
the planets revolve around the Sun.
(16k jpg;
86k jpg;
more;
yet more)
Dutch-born American astronomer best known for his study of the surface of the
Moon; discovered Miranda
and Nereid,
found an atmosphere on Titan.
(Dr.Kuiper was solidly Americanized; his name is pronounced to rhyme with "viper.")
(a short bio
French
(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.
(5k gif)
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.
(more and
more)
British astronomer, discovered Neptune's
largest satellite, Triton and (with
Bond) discovered
Saturn's moon
Hyperion.
A successful brewer before turning to astronomy.
(22k jpg;
more)
French mathematician whose prediction of the position of an undiscovered
planet (Neptune)
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.
American astronomer. He founded the Lowell Observatory in Arizona (1894),
where his
studies
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.
(26k gif)
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.
(a.k.a. Mayr) German astronomer who gave Jupiter's
"Galilean" moons
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.
(more)
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". (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 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.
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
Einstein's famous
equivalence E=mc2. This is the source of the Sun's
energy therefore ultimately of (almost) all energy on Earth.
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.
(more;142k gif)
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)
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)
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.
(more)
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.
Discovered Phoebe.
planet
An object orbiting a star that is not a brown dwarf but bigger than an asteroid. This is somewhat ambiguous. In our solar system it is really an historical definition which boils down to "a planet is a member of the set {Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto}". All the known planets orbiting other stars are large gas planets so no ambiguity yet arises there. But when we begin to discover terrestrial planets and then smaller objects it will become necessary to make some further arbitrary definition.
(aka Claudius Ptolemaeus) Alexandrian astronomer, mathematician,
and geographer who based his
astronomy on the belief that all heavenly bodies revolve around the Earth.
(10k gif;
more)
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
Nobel prize
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)
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
north pole.
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
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.
(more)
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.
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).
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.
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 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.
= 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.
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.
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.
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).
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.
an object orbiting in the Lagrange points of
another (larger) object. This name derives from a generalization of the
names of
some of the largest asteroids in
Jupiter's
Lagrange points: 588 Achilles, 624 Hektor, and 911 Agamemnon.
Saturn's satellites
Helene,
Calypso and
Telesto are also sometimes called Trojans.
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.
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.
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
Earth and Io are young; the
surfaces of Mercury and
Callisto are old.
Glossary
... Plea
... Glossary
... Appendices
... Data
