A
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
Le Verrier. |
antipodal point
the point that is directly on
the opposite side of the planet |
asteroid
(also "planetoid") a medium-sized
rocky object orbiting the Sun; smaller than a planet, larger than a
meteoroid |
astronomical unit (AU)
= 149,597,870 km; the
average distance from the Earth
to the Sun. At 100 miles per hour (160 kph) it would take over 100 years
to go 1 AU. |
aurora
a glow in a planet's ionosphere caused
by the interaction between the planet's magnetic field and charged
particles from the Sun |
aurora australis
the "Southern Lights";
caused by the interaction between the solar wind, the Earth's magnetic
field and the upper atmosphere. A similar effect happens in the northern
hemisphere where it is known as the aurora borealis or "Northern
Lights". |
axis
an
imaginary straight line around which an object rotates or spins.
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B
Bailey's Beads
are bright spots of light that
appear around the rim of the solar disk just before an eclipse. The spots
are roughly the same size, and look like a string of pearls. Baily was a
British astronomer [1774-1844]. |
billion
A "billion" in the U.S.A. means
1,000,000,000 (1e9);
The British version of one billion means 1e12.
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C
caldera
crater formed by an explosion or
collapse of a volcanic vent. |
coma
the dust
and gas surrounding an active comet's nucleus |
comet
a medium-sized, icy object orbiting the
Sun; smaller than a planet |
Copernicus, Nicolaus 1473-1543
Polish
astronomer who advanced the heliocentric
theory that the Earth and other planets revolve around the Sun.
The Ptolemaic
view of the universe was the prevailing theory for over 1000 years.
(The heliocentic idea was first put by Aristarcus of Samos in the 3rd
century BC.) |
corona
the uppermost level of the solar
atmosphere, characterized by low densities and high temperatures.
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crater
bowl-shaped depression formed by the impact of a meteoroid;
depression around the opening of a volcano. |
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D
density
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. |
disaster
literally "bad stars"; particularly
suitable in reference to a major asteroid impact. |
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E
eclipse
The hiding or blocking of one celestial object from
another.
A solar eclipse occurs when the moon comes between the
Sun and the observer. This happens when the shadow cone of the Moon
touches the surface of the Earth, and is observable by anyone within this
shadow zone. |
ellipse
oval. The orbits of the planets are
ellipses, not circles. This was first discovered by Johannes Kepler based
on the careful observations by Tycho Brahe. |
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.
To change a number in
exponential notation into one that makes sense, all you have to do is move
the decimal point the last number of places to the right. |
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F
fireball
a meteor
brighter than magnitude -3 |
flare
a
sudden eruption of energy on the Sun lasting minutes to hours, from which
radiation and particles are emitted. |
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G
Gaia Hypothesis
named after the Greek Earth
goddess Gaea, holds that the Earth should be regarded as a living organism
and that biological processes stabilize the environment. |
Galle,
Johann Gottfried 1812-1910
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 to Le Verrier. |
Galilean Moons
Jupiter's
four largest moons: Io, Europa, Ganymede and Callisto.
These were
discovered independently by Galileo
and Marius. |
Galileo Galilei 1564-1642
Italian astronomer
and physicist. The first to use a telescope to study the stars. 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 imprisoned Galileo. The Church kept this belief
for 350 years; Galileo was formally exonerated in 1992. |
George
III 1738-1820
King of Great Britain and Ireland (1760-1820). His government's policies
led to the American War of Independence in 1776 and to the colonization
of Australia. |
greenhouse effect
increase in temperature
caused when solar radiation is passes through the atmosphere to Earth but
the thermal radiation leaving the Earth is blocked by carbon dioxide,
water vapor and other particles in the atmosphere).
The greenhouse
effect is very important on Venus
and Earth
but very weak on Mars.
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H
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.
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heliocentric
Sun-centered; see Copernicus
and Galileo.
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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. |
Huygens, Christiaan 1629-1695
Dutch physicist
and astronomer who first described the nature of Saturn's
rings (1655) and discovered its moon Titan. |
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I
ice
used by planetary scientists to refer to
water, methane, and ammonia which usually occur as solids in the outer
solar system. |
inclination
the inclination of a planet's
orbit is the angle between the plane of its orbit and the ecliptic (the
plane of the Sun's orbit). |
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. |
ionosphere
a region of charged particles in a planet's upper atmosphere; the part
of the Earth's atmosphere beginning at an altitude of about
15 kilometers and extending outward 150 kilometers or more. |
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K
Kelvin (K)
0 Kelvin is absolute zero;
ice
melts at 273 K;
water boils at 373 K. |
Kepler, Johannes 1571-1630
German astronomer
and mathematician. Considered a founder of modern astronomy. Using the
positional data carefully collected by Tycho Brahe, Kepler formulated the
famous three laws of planetary motion. |
kilogram (kg)
= 1000 grams = 2.2 pounds, the mass of a elite of water. |
kilometer (km)
= 1000 meters = 0.62 miles. |
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L<
a>
Lassell, William 1799-1880
British astronomer,
discovered Neptune's
largest satellite, Triton and (with Bond) discovered Saturn's
moon Hyperion. |
Le
Verrier, Urbain Jean Joseph 1811-1877
French mathematician
whose prediction of the position of an undiscovered planet (Neptune)
that caused disruptions 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.
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light-year
= 9.46053e12 kilometers (= 5,880,000,000,000 miles = 63,239 AU);
the distance traveled by light in a year. |
Lowell, Percival 1855-1916.
American
astronomer. He founded the Lowell Observatory in Arizona in 1894, where
his studies of Mars
led him to believe that the linear markings on the surface were "canals"
and therefore that the planet was inhabited by intelligent beings. His
successors later discovered Pluto.
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lunar month
The average time between
successive new or full moons,
equal to 29 days 12 hours 44 minutes.
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M
meteor
(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.
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meteorite
a rock of extraterrestrial origin found on Earth |
meteoroid
a small rocky object orbiting the
Sun;
smaller than an asteroid |
minor
planets
the term used for asteroids.
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N
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 Einstein's famous equivalence E=mc2. This is the source of the
Sun's energy therefore of almost all energy on Earth. |
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O
orbit
The closed path of one object around another.
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P
photosphere
the visible surface of the
Sun. |
prominence
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. |
Ptolemy 87-150
Alexandrian astronomer,
mathematician, and geographer who based his astronomy on the belief that
all heavenly bodies revolve around the Earth. |
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R
retrograde
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 north pole is the
one on the same side of the ecliptic as the Earth's north pole.
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revolve
to
turn in a circle or move in an orbit |
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S
satellite
A small object in space orbiting a larger one.
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shepherd satellite
(or 'shepherd moon') a
satellite which constrains the extent of a planetary ring through
gravitational forces. |
sidereal
relating to, or concerned with the
stars. |
solar nebula
the cloud of gas and dust
that began to collapse about 5 billion years ago to form the solar system.
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Solar system
the system dominated by the
Sun and including the Planets, Minor Planets, Comets, planetary satellites
and interplanetary debris that travel in orbits around the Sun.
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Solar wind
a 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). |
sunspot
an area seen as a dark spot on the photosphere
of the Sun.
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.
(Mercury and Venus are called "inferior"
planets.) |
T
Tombaugh, Clyde 1906-1997
American
astronomer; discovered Pluto.
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