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Glossary

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Science  

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Solar System Glossary
A B C D E F G H I K L M N O P Q R S T
Click on a letter
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.
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.
heliocentric
Sun-centered; see Copernicus and Galileo.
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.
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.
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.
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.
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.
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.
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.
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.
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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