A

51 Pegasi

absolute magnitude

accretion disc

acetylene

Adrastea

Amalthea

ammonia

Andromeda

annular eclipse

Aphrodite Terra

argon

asteroid belt

asteroids

atmosphere

atmospheric pressure

axis

B

Big Bang

binary stars

biochemical reactions

black hole

Bootes

C

Callisto

Canis Major

carbon

carbon dioxide

Cassini

Cassiopeia

Clementine

Centaurus

Ceres

Charon

Christian Huygens

Clyde Tombaugh

coma

comets

continental plates

convection

Copernicus (crater)

corotation circle

Cydonia

Cygnus

D

Danjon Scale

Deimos

diameter

Didier Queloz

E

Earth's mantle

eccentric orbit

electrons

elliptical orbit

Enceladus

Eros

ESA

Eta-Aquarids

ethane

Europa

extremophiles

F

four basic forces

Frank Drake

fusion

G

galaxy-elliptical

galaxy-irregular

galaxy-lenticular

galaxy-spiral

Galileo (spacecraft)

Galileo Galilei

Ganymede

gas planets

Gaspra

Gemini

Geminids

Gerard Kuiper

Giotto (spacecraft)

glacier

Gliese 581

globular cluster

Grand Canyon

gravity

Great Red Spot

greenhouse effect

Guiseppe Piazzi

H

Halley's Comet

Heinrich Olbers

helium

Horsehead Nebula

hot springs

Huygens (spacecraft)

hydrocarbons

hydrogen

hydrothermal vents

I

Ida

interstellar

Io

ion tail

iron

Ishtar Terra

J

Jovian moons

K

kelvin

Kepler (crater)

Kuiper Belt

L

Large Magellanic Cloud

Leo

Libra

light year

Lira

luminosity

lunar maria

M

M13

M42

M57

Magellan (spacecraft)

magnetic field

main sequence stars

maria

Mariner 2

Mariner 10

Mars Express

Mars Global Surveyor

Mars Recoinnassance Orbiter

Mars Science Laboratory

mass

Maxwell Montes

Messenger (spacecraft)

meteor

meteorites

meteoroids

methane

methanol

Metis

Michel Mayor

Milky Way

Mount Everest

multiple star system

N

NASA

NEAR

neon

neutrinos

neutron star

neutrons

nitrogen

nuclear fusion

nucleus

O

oceanic plates

Odyssey (space craft)

Olympus Mons

Oort Cloud

open star cluster

orbit

orbital resonance

Orbiter 1

Orion

OSETI

oxygen

ozone

P

Pallas

partial eclipse

Pegasus

penumbra

permafrost

Perseids

Perseus

Phobos

photons

photosynthesis

Pioneer 10

Pioneer 11

planetary nebula

Pleiades

primordial

Project Phoenix

prominences

protogalaxy

proton

Proxima Centauri

Q

Quadrantids

quark

R

radius

radio waves

red dwarf

red shifts

runaway greenhouse effect

S

Saggitarius Dwarf Elliptical Galaxy

Shoemaker-Levy 9

silicate

Skylab

Small Magellanic Cloud

smog

SOHO (spacecraft)

solar corona

solar eclipse

solar prominences

Solar System

solar wind

speed of light

Stardust (spacecraft)

subduction zones

sulfolobus shibatae

sulfuric acid

sunspots

supergiants

supernovas

T

Taurus

tectonic activity

tectonic plates

Thebe

tidal forces

tidal locking

tidal resonance

total eclipse

totality

triple stars

Tycho Brahe

Tycho (crater)

U

Ulysses (spacecraft)

U

umbra

Ursa Major

Ursa Minor

UV

V

Valles Marineris

Venera 7

Venera 9

Venus Express

Vesta

Viking 1

Virgo

Virgo cluster

Voyager (spacecraft)

Voyager 1

Voyager 2

W

white dwarf

Y

yellow dwarf






51 Pegasi

A yellow dwarf star found in the constellation Pegasus.
In 1995 it became the first star other than our Sun, to be found to have a planet orbiting around it.

absolute magnitude

The brightness of a star as seen from a standard distance, defined as 10 parsecs.

accretion disk

A structure formed when material in space is pulled by the gravity of a massive object, such as a star or a black hole, slowly compressing it into a spiral shaped disk as it's pulled in.

acetylene

C2H2
A hydrocarbon and colorless gas often found in the atmospheres of gas giants, such as Saturn.

Adrastea

Jupiter's second moon, discovered in 1979 by David C. Jewitt and G. Edward Danielson from Voyager 2 photographs.
It measures 20 x 14 x 16 kilometers.

Amalthea

Jupiter's third moon, discovered in 1892 by Edward Emerson Barnard.
It measures 250 x 146 x 128 kilometers.

ammonia

NH3
A colorless gas and a compound of nitrogen and hydrogen.

Andromeda

A spiral galaxy, also known as Messier 31 (M31),located about 2.5 million light years away.
Also the name of the constellation in which the Andromeda Galaxy is found.

annular eclipse

One of the four types of solar eclipses, an annular eclipse happens when the Moon and Sun are perfectly aligned but the Moon does not cover the Sun completely, resulting in the Sun appearing as a bright ring in the sky.

Aphrodite Terra

A highland area on the planet Venus, marked by numerous fractures and lava flows and located near the planet's equator.
The computer-generated topography image above shows the Latona Corona and Dali Chasma on Aprodite Terra.

argon

A colorless and odorless element, it's the third most common gas in the Earth's atmosphere.

asteroid belt

The area between the orbits of Mars and Jupiter which contains a large number of asteroids, including Ceres, the largest asteroid in the Solar System.

asteroids

Objects in the Solar System which orbit the Sun, but are too small to be considered planets.
Ceres, the larges known asteroid, has a diameter of just under 500 kilometers.

atmosphere

The gaseous material surrounding planets; the air surrounding Earth.

atmospheric pressure

The pressure caused by the weight of a planet's atmosphere.

axis

A straight line around which an object rotates.

Big Bang theory

The scientific explanation for the origin of the universe, championing the notion that the universe spontaneously originated 15 billion years ago in a colossal explosion.

binary star

A two-star system, where the individual stars orbit their common center of mass, often appearing to revolve around each other.

biochemical reaction

The process in which one chemical substance is transformed into another.

black hole

A location in space with very high mass and density; gravity prevents anything, including light from escaping such a region.

Bootes

A constellation in the northern sky, containing the third brightest star in the sky, Arcturus.

Callisto

One of the four Galilean satellites, and the second largest of Jupiter's moons.
It was discovered in 1610 by the Italian astronomer and mathematician, Galileo Galilei.

Canis Major

A constellation which is home to Sirius, the brightest star in the sky.

carbon

The fourth most abundant element in the universe, carbon is the basis for life on Earth.

carbon dioxide

CO2
A colorless gas consisting of one carbon atom bound to two oxygen atoms.

Cassini

Launched in 1997, and a joint venture between NASA, ESA and ASI, the Cassini satellite has been orbiting Saturn since 2004 and has been responsible for the data which has resulted in the discovery of seven new moons orbiting Saturn.
It also carried the Huygens probe, which landed on the surface of the moon, Titan, in 2005.

Cassiopeia

A constellation in the northern sky and home of the Ρ Cas (Rho Cassiopeiae) and V509 Cas yellow hypergiant stars.

Clementine

A satellite launched on January 1994 and built to make observation of the Moon and the asteroid 1620 Geographos. The mission was ended in June of the same year.

Centaurus

A constellation found in the southern sky, and home of the Alpha Centauri triple star system.

Ceres

The only dwarf planet in the inner Solar System, with a diameter of 950 kilometers, and the largest object found in the asteroid belt, between the orbits of Mars and Jupiter.
It was discovered in 1801 by the Italian astronomer and priest, Giuseppe Piazzi.

Image credit: NASA/ESA/J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI)

Charon

The largest satellite of the dwarf planet Pluto, with a radius of about 600 kilometers. It was discovered in 1978 by James Christy.

Photo of Pluto and Charon courtesy of NASA/JPL-Caltech.

Christian Huygens

Dutch astronomer and mathematician, born in 1629, who discovered Saturn's moon, Titan.
Also known for his studies and observations of the Orion Nebula, as well as his work in optics and physics.

Clyde Tombaugh

American astronomer born in 1906 who, while working as a researcher at the Lowell Observatory in Arizona, discovered the dwarf planet Pluto. He is also known for having discovered nearly 800 asteroids, several star and galaxy clusters and is partially responsible for the discovery of the Pisces-Perseus supercluster.

Pluto's orbit

comet

An ice-rock body composed of ice and nonvolatile dust, constituted mainly of frozen water or gas. Comets typically have five parts: a nucleus, a hydrogen cloud, a coma, a dust tail, and an ion tail.

continental plates

Regions of the Earth's outer rocky crust that are divided into huge sections that overlap continents and the shallow sea beds that surround them.

convection

The process of heat transfer in a gas or a liquid through the circulation of hotter material from a warmer area to a cooler one.

Copernicus (crater)

A large crater located on the Moon's Oceanus Procellarum and named after Nicolai Copernicus. It is 93 kilometers in diameter.

corotation circle

The area inside the disk of a spiral galaxy which rotates around the galaxy's nucleus at the same rate as the galaxy's spiral arms.

Cydonia

A region on the planet Mars, famous for being the location of the geological formation known as the "Face on Mars."

Cygnus

Also known as the Northern Cross, Cygnus is a constellation visible in the northern hemisphere during the summer and autumn months. The blue supergiant Deneb is its biggest star.

Danjon scale

A five-point scale used to measure the appearance of the Moon during a lunar eclipse:

  1. Very dark eclipse. Moon almost invisible, especially at greatest eclipse.
  2. Dark Eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
  3. Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.
  4. Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
  5. Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.

Deimos

The smallest and outermost of Mars's two moons, it measures 15 x 12.2 x 10.4 kilometers.

diameter

A straight line passing through the center of a figure, usually a circle, and whose endpoints lie on the periphery of the figure.

Didier Queloz

A Swiss astronomer, who along with Michel Mayor, discovered 51 Pegasi in 1995.

Earth's mantle

The layer between Earth's rocky crust and it's molten inner core.

Illustration: Gabriel Alvarado-Marin, SETI Institute

eccentric orbit

An orbit that's elliptical, deviating from circular. The orange planet has an eccentric orbit, while the blue planet's is circular.
The same as elliptical orbit.

electron

A negatively charged particle that partially comprises an atom.

elliptical orbit

An orbit that's elliptical, deviating from circular. The orange planet has an elliptical orbit, while the blue planet's is circular.
The same as eccentric orbit.

Enceladus

The sixth largest of Saturn's moons, discovered by William Herschel in 1789.
In 2005, plumes of icy liquid were discovered shooting of its south pole .

Eros

An S-type (stony) asteroid discovered in 1898. It measures 34.4 x 11.2 x 11.2 kilometers in size.

Photo courtesy of NASA/JPL/JHUAPL

ESA

The European Space Agency, founded in 1975 and headquartered in Paris, France.

Eta-Aquariids

The meteor shower associated with Halley's Comet and visible from April to May each year.

ethane

C2H6
A colorless and odorless gas found in trace amounts in Earth's atmosphere. It has also been detected in small amounts in the atmospheres of all four gas giant planets as well as Saturn's moon, Titan.

Europa

The smallest of Jupiter's four Galilean satellites, it was discovered in 1610 by the Italian astronomer and mathematician, Galileo Galilei.
It is believed that there is a deep layer of water underneath its icy surface.

extremophiles

Organisms that can survive in environments that would be deadly to other life forms.

Four Basic Forces

Also known as the four fundamental interactions, they describe the ways in which particles interact with one another.

  1. Strong force: Binds protons and neutrons together and is thus responsible for forming of nuclei in atoms.
  2. Electromagnetic force: the force that dictates how particles with an elecric charge behave with one another.
  3. Weak force: responsible for the radioactive decay in subatomic particles.
  4. Gravitational force: the force which causes objects to be attracted to one another and is directly related to an object's mass.

Frank Drake

American astronomer and astrophysicist and a pioneer in the search for extraterrestrial intelligence. He is also one of the founders of the SETI Institute.

fusion

Nuclear fusion is the process by which the nuclei of two atoms fuse together to form a heavier element; large amounts of energy are produced by this fusion.

galaxy - elliptical

A type of galaxy ranging in shape from almost spherical more elongated ellipsoid shapes. Elliptical galaxies have no spiral arms.

Photo credit: Robert Gendler (www.robgendlerastropics.com)

galaxy - irregular

A galaxy without the clearly defined shape of lenticular, spiral or elliptical galaxies.

Image credit: Local Group Galaxies Survey Team, NOAO/AURA/NSF

galaxy - lenticular

A type of galaxy made up of a flat disk and central bulge, but lacking the spiralling arms of a spiral galaxy.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)

galaxy - spiral

A type of galaxy consisting of a flat spinning disk, a central bulge made up of old stars, and two or more "arms" spiraling from the center.

Photo credit: Robert Gendler (www.robgendlerastropics.com)

Galileo (spacecraft)

Launched in 1989, Galileo was a spacecraft tasked with the mission of studying Jupiter and its moons.
In 2003, the mission was ended and Galileo was purposely hurled into Jupiter's atmosphere.

Illustration courtesy of NASA

Galileo Galilei

Italian astronomer, mathematician and physicist best known for his defense of heliocentrism and for the discovery of Jupiter's four largest moons.

Illustration: Gabriel Alvarado-Marin (SETI Institute)

Ganymede

One of the four Galilean Satellites and the largest moon in the Solar System.
Discovered by Galileo Galilei in 1610, it has a radius of 2,634 kilometers.

gas planets

Planets that are composed mostly of gaseous material, rather than rocky or solid material.
The four planets in the outer Solar System are all gas planets.

Gaspra

Also known as 951 Gaspra, it is an S-Type (stony) asteroid orbiting within the confines of the asteroid belt. It measures 18.2 x 10.5 x 8.9 kilometers.

Photo courtesy of NASA/JPL/USGS

Gemini

One of the zodiac constellations and home to the stars Castor and Pollux.

Geminids

A meteor shower associated withe the asteroid 3200 Phaethonand visible every December.

Gerard Kuiper

Dutch-American astronomer known for his discovery of the moons Miranda (Uranus) and Nereid (Neptune), as well as numerous binary stars. The Kuiper belt is named in his honor.

Giotto (spacecraft)

Launced in 1986 by ESA, Giotto was tasked with approaching and studying Halley's Comet.

glacier

A huge and very slow moving body of ice formed by the accumulation of compacted snow.

Gliese 581

A red dwarf star located in the constellation Libra.

globular cluster

A very dense grouping of stars existing inside or next to a galaxy, containing anywhere from 100,000 to 1 million stars.

globular cluster

A very dense grouping of stars existing inside or next to a galaxy, containing anywhere from 100,000 to 1 million stars.

gravity

One of the fundamental forces of physics; gravity is responsible for the attraction of bodies on the surface of a planet to the mass of the planet.

Great Red Spot

An oval-shaped storm, twice the size of Earth and located near the equator of the planet Jupiter. It has been observed from Earth for the last 300 years.

Greenhouse effect

The effect in which the gases of a planet's atmosphere, such as carbon dioxide and methane, allow sunlight to pass in and reflect back out, but trap most of the heat energy reflected from the surface of the planet, resulting in an increase in surface temperature.

Giuseppe Piazzi

Italian astronomer and priest, born in 1746 and best known for his discovery of Ceres, the largest object in the asteroid belt.

Illustration: Gabriel Alvarado-Marin (SETI Institute)

Halley's Comet

A comet visible on Earth every 75 years and last seen in 1986.
It's been observed for at least 2,000 years, but it was British astronomer Edmund Halley who realized that it was the same object that made periodic passes, and not individual objects as first thought.
Halley's comet won't be seen again until 2061.

Heinrich Olbers

German astronomer and physician, best known for his discovery of the asteroids Pallas, in 1802, and Vesta, in 1807.

helium

A colorless and oderless single-atom gas, it is the second most abundant element in the universe.

Horsehead Nebula

A dark nebula in the constellation Orion.

Photo Credit and Copyright: Nigel Sharp (NOAO), KPNO, AURA, NSF

hot springs

A spring is a source of water that flows to the surface from somewhere underground.
A hot spring is a spring which has a water source that has been geothermally heated.

Huygens probe

A probe which flew as part of ESA's Cassini-Huygens mission, launched in 2004, and was tasked with descending through the atmosphere of Saturn's moon, Titan.
It landed on Titan's surface in 2005 and succeeded in sending 350 images to the orbiting Cassini, which then relayed the images to Earth.

hydrocarbons

A chemical compound made solely of hydrogen and carbon.

hydrogen

The most common element in the Universe and the main fuel of stars.

hydrothermal vents

Similar to geysers or hot springs, these are fissures on the sea floor which emit geothermally heated water.

Ida

An S-type asteroid found in the asteroid belt, Ida was the first asteroid to be found with a satellite (Dactyl) orbiting it.

Photo courtesy of NASA/JPL

interstellar

Between stars.

Io

One of the four Galilean moons, and the fourth largest moon in the Solar System.
Discovered by Galileo Galilei in 1610, it has a radius of 1821 kilometers.

ion tail

The tail of ionized gas that is formed as a result of the pushing of the solar wind on the coma of a comet.

iron

A metal and the most common element on Earth.

Ishtar Terra

A large, highland region on the planet Venus, located near the north pole.
The image above shows a portion of the region, with Maxwell Montes shown in red. The image was generated from radar data gathered by Pioneer Venus Orbiter.

Jovian moons

The moons of Jupiter, of which there are 64 known.

kelvin

A unit of measure for temperature.
A temperature of 0 kelvin is equal to -273.15° C and -459.67° F.
310.95 kelvin is equal to 100° F and 37.8° C.

Kepler (crater)

Kepler is the name of two different craters in the Solar System: one on the Moon, between Oceanus Procellarum and Mare Insularum; and the other on Mars, in the Eridania quadrangle.

Kuiper belt

A region in the Solar System that extends beyond the orbit of Neptune and is the home of remnants from the formation of the Solar System, as well as the dwarf planet Pluto.

Large Magellanic Cloud

Viewable from the southern hemisphere, the LMC is an irregular-shaped galaxy that is one of several satellite galaxies of the Solar System. It is 157,000 light years away.

Leo

One of the zodiac constellations and home to the stars Regulus, Denebola and Algieba.

Libra

One of the zodiac constellations and home to the stars Gliese 581, Zubenelgenubi, Zubeneschamali, Zubenelakrab, Brachium.

light year

A unit of measure, it is the distance that light travels in one year. It is equivalent to aproximately 5.879 trillion miles.

Lyra

A constellation visible in the northern hemisphere and home to the stars Vega and Sheliak.

luminosity

The amount of light put out by a star.

Lunar maria

Mare is Latin for ocean (plural: maria) and it refers to the dark patches on the Moon, many of which are ancient lava flows.

M13

Also known as Messier 13, it is a globular cluster found in the constellation of Hercules and consisting of about 300,000 stars. It was discovered by Edmund Halley in 1714.

In 1974, the Arecibo Message, written by Frank Drake and Carl Sagan, was broadcast from the Arecibo radio telescope in Puerto Rico.

M42 - the Orion Nebula

Messier 42, also known as the Orion nebula, is a nebula located just south or Orion's belt, seen as on of the points of light in Orion's sword.

M57 - the Ring Nebula

Messier 57, more popularly known as the Ring Nebula, is a planetary nebula located in the constellation Lyra, south of Vega, Lyra's brightest star.

Credit: H. Bond et al., Hubble Heritage Team (STScI / AURA), NASA

Magellan (spacecraft)

Launched by NASA on 1989 with the task of mapping the surface of Venus, it completed 4,225 orbits and mapped 98% of the planet's surface before ending its mission on September 1994.

magnetic field

A condition generated by electrons moving through space.

main sequence stars

Average and stable mid-phase stars, as plotted along the diagonal top right to bottom left band of the Hertzprung-Russell diagram.

mare (plural: maria)

Latin for ocean, these are large plains found on the Moon.

Mariner 2

Launched on August 1962 by NASA, and a replacement for the destroyed Mariner 1, Mariner 2 became the first spacecraft to fly by another planet when it flew past Venus four months later.

Mariner 10

Launched on November 1973 by NASA, Mariner 10 was the last spacecraft of the Mariner program. It was the first spacecraft to utilize a gravity-assisted trajectory, a technique that uses the gravitational attraction of one planet to propel a spacecraft towards its next goal in order to conserve both fuel and power.

Image credit: NASA

Mars Express

Launched by the ESA on June 2003, Mars Express and its lander, the Beagle 2, were tasked with examining the biology and geology of Mars.

Contact with the Beagle 2 was lost shortly after landing, but the Orbiter has been able to continously conduct measurements of Mars since early 2004.

Mars Global Surveyor

Launched on November 1996 by NASA, the MGS was able to study the climate of Mars and to map out its surface in high resolution detail before losing communication on 2006.

Mars Reconnaissance Orbiter

MRO's mission goals were to view the surface of Mars at as high a resolution as possible from orbit to help NASA better understand about landing sites for the rovers Spirit and Opportunity.

MRO launched on August 2005 and has returned extremely high resolution photographs of the surface of Mars, subsurface data and measurements of the temperature and water vapor levels in the Martian atmosphere.

Mars Science Laboratory

Presently scheduled to launch late 2011, the MSL is a NASA mission that will carry direct onboard chemical analysis of Martian soils and ground rock powders, and look for organic and carbon compounds.

mass

The amound of matter in an object, measured in kilograms. Mass is different from weight, which is measured in pounds and can only be measured under acceleration such as a gravity field. A 1-kilogram mass weighs about 2.2 pounds on the surface of Earth, but weighs only 0.8 pounds on the surface of Mars.

Maxwell Montes

A mountain on the planet Venus located on Ishtar Terra. At a height of 11 kilometers, it is the highest peak on the planet.

Messenger (spacecraft)

The second spacecraft to reach Mercury (after Mariner 10), Messenger is a NASA mission studying the geology and magnetic field of that planet.

It was launched on August 2004 and entered Mercury's orbit on March 2011.

meteor

Seen as a bright streak in the sky (sometimes called a shooting star or falling star) it is a tiny grain of dust or pebble that burns up when it hits Earth's atmosphere. Meteors come from comets and other space debris.

meteorite

A meteor that survives passage through the atmosphere and crashes into Earth.

meteoroid

A small piece of rock or dust floating freely in space, before they enter Earth's atmosphere and burn up as meteorites.

methane

CH4

A colorless, odorless gas and the main component of natural gas.

methanol

CH3OH
A colorless, flamable liquid, commonly used as antifreeze.

Metis

The innermost moon of Jupiter, discovered in 1979 from photographs taken by Voyager 1.
It measures 60 x 40 x 34 kilometers.

Michel Mayor

Swiss astronomer and emeritus professor at the University of Geneva. In 1995, he and Didier Queloz discovered the first exoplanet, 51 Pegasi b.

Milky Way

The galaxy to which the Solar System belongs. It is a barred spiral galaxy and home to 200-400 billion stars.

Mount Everest

Earth's highest mountain, with a peak of 8,848 meters and located in Nepal, near the border with Tibet.

multiple star system

A star system containing three or more stars (but less than what is found in an open star cluster) which orbit each other.
Most multiple star systems are triple star systems, but there are quadruple, quintuple, sextuple star systems, and more.
The star systemNu Scorpii, in the Scorpio constellation, is believed to be a septuple star system, containing seven stars orbiting around one another.

NASA

The National Aeronautics and Space Administration, headquartered in Washington D.C. Founded in 1958, the American space agency has been responsible for a number of remarkable breakthroughs in aeronautics and space exploration.

NEAR

The Near Earth Asteroid Rendezvous, launched in 1996 by NASA, is a space probe designed to study the asteroid Eros.
Even though NEAR was never intended to be a lander, in early 2001 the probe was commanded to land on Eros's surface, which was possible in part due to the low gravity of the asteroid.

Neon

A gas that though rare on Earth, is the fifth most common element in the universe.

Neutrinos

Electrically neutral, sub-atomic particles which are created in some nuclear reactions, such as can be found in certain stars and supernovae. Because they have no electric charge, they are not affected by electromagetic forces.
There are three types of neutrinos which are named according to the charged particle to which they are associated:

  1. Electron neutrino
  2. Muon neutrino
  3. Tau netrino

Neutron star

A very dense core of material that forms after a star explodes.

Neutrons

Nuclear subatomic particles located inside the nucleus of most atoms; simple hydrogen is the exception.

Nitrogen

A colorless and odorless gas, and one of the most abundant elements in Earth's atmosphere, and the seventh most abundant element in the Universe.
Nitrogen is a byproduct of the fusion process that occurs in stars.

nuclear fusion

The process by which the nuclei of two atoms fuse together to form a heavier element; large amounts of energy are produced by this fusion.

nucleus

The core of an atom, which contains its protons and neutrons.

Oceanic plates

The large segments of the Earth's crust the mostly make up the floor of the world's oceans. These plates are commonly made up of solidified basaltic lava and float on top of the Earth's mantle.

Odyssey (spacecraft)

The 2001 Mars Odyssey is a robotic probe launched by NASA in 2001 with the purpose of looking for evidence of volcanic activity and water on the surface of Mars.
It was launched in 2001 and is still functioning and orbiting Mars.

Olympus Mons

A huge volcanic mountain located on the west side of the Tharsis region on the planet Mars, Olympus Mons is three times taller than Mount Everest. It was discovered from photographs taken by Mariner 9.

Oort cloud

A cloud of primitve material surrounding the Solar System at great distances.
Tho Oort cloud also extends above and below the Solar System's plane, so long-period comets have large inclinations, and dip above and below the plane of the Solar System on their trip around the Sun.

Open star cluster

Groupings of stars that are less dense than globular clusters, containing no more than a few thousand stars and generally lacking a central core.

Orbital period

The time taken by an object to do a complete orbit around another object.

Orbital resonance

The condition resulting from a two-planet or satellite system where one orbital period is twice that of the other.
Resonances are possible with more than two planets; three of the Galilean satellites of Jupiter are in 1:2:4 resonances with one another.

Orbiter 1 (Viking)

The Viking 1 mission, launched in 1976 by NASA, consisted of a two-part unit: a lander designed to take Martian soil samples and send the data back to Earth; and an orbiter which carried the lander and took photos of the surface of Mars.

Orion

One of the most well-known constellations in the sky, Orion is home to the stars Betelgeuse and Rigel, as well as M42 -- the Orion Nebula.

OSETI

The optical search for extra-terrestrial intelligence, which attempts to detect pulsed laser signals as sent by other civilizations.

Oxygen

The third most abundant element in the universe and a key component of the air we breathe.

Ozone

A triatomic molecule, made up of three oxygen atoms.
Ozone is a large part of Earth's ozone layer, which absorbs most of the Sun's damaging ultraviolet light.

Pallas

Discovered in 1802 by Heinrich Wilhelm Olbers, Pallas is one of the largest asteroids in the asteroid belt.

Partial eclipse

The partial obscuring of one celestial body by another.

Pegasus

A constellation in the northern sky and home to the stars Markab and Scheat. It is also home to 51 Pegasi, the first star outside of our own to have been found to have a planet orbiting it.

Penumbra

The outer, lighter colored area of a sunspot that surrounds the umbra.

Permafrost

Thick sections of permanently frozen soil.

Perseids

The meteor shower associated with the comet Swift-Tuttle, the Perseids are visible from mid-July to mid-August every year.

Perseus

A constellation visible in the northern sky, it is the home of the stars Algol and Mirfak and the location in the sky of the Perseids meteor shower.

Phobos

The largest of the two moons of Mars, measuring 26.8 x 22.4 x 18.4 kilometers.
It was discovered in 1877 by American astronomer Asaph Hall.

Photons

A unit of light intensity, or a quantum when referring to electromagnetic radiation.

Photosynthesis

The chemical process by which green plants, using sunlight, convert carbon dioxide into organic compounds, generating oxygen as a byproduct.

Pioneer 10

Launched on March 2, 1972. The first probe to successfully make the trip through the asteroid belt and to Jupiter.

Pioneer 11

Launched on Arpil 5, 1973, Pioneer 11 also made it to Jupiter and sent valuable images of the Galilean moon, Callisto. Using Jupiter's gravity, it then changed trajectories and headed towards Saturn, from which it sent images of the giant planet's moons and rings.

Planetary nebula

Gas ejected from a star that is approaching the end of its life; resembled a planet to early telescopic observers.

Pleiades

An open star cluster located in the constellation Taurus, containing hundreds of stars. The seven brightest, Sterope, Merope, Electra, Maia, Taygeta, Celaeno, and Alcyone, are named after the Seven Sisters of Greek Mythology.

Primordial

From the beginning, original, earliest, prehistoric.

Prominences

Large plumes of plasma emitted from the Sun's surface, which extend into the Sun's corona before looping back.

Project Phoenix

Begun in 1995, Project Phoenix was the world's most sensitive and comprehensive search for extraterrestrial intelligence. It was an effort to detect extraterrestrial civilizations by listening for radio signals that were either being deliberately beamed our way, or were inadvertently transmitted from another planet. Phoenix was the successor to the ambitious NASA SETI program that was cancelled by a budget-conscious Congress in 1993, and it ceased operations in 2004, after plans for the Allen Telescope Array where unveiled.

Proto galaxies

Huge clouds of gas which are on their way to forming galaxies.

Proton

A positively charged subatomic particle that is located inside the nucleus of an atom.

Proxima Centauri

A red dwarf star located in the constellation Centaurus. At 4.2 light years away it is the nearest star to Earth, other than the Sun.
It was discovered in 1915 by the Scottish astronomer, Robert Innes.

Quadrantids

A January meteor shower best viewed in nothernmost latitudes.

Quark

A hypothetical particle believed to be a fundamental part of hadrons (particles such as protons and neutrons).
There are six different types (flavors) of quarks: up quark, down quark, top quark, bottom quark, charm quark, and strange quark.

Radius

A line segment that extends from the center of a circle or sphere to its perimeter.

Radio waves

A type of electromagnetic radiation with long wavelengths that put it outside of the range of the visible spectrum.

Red dwarf

A small and relatively cool star, about half the mass the size of our Sun and with temperatures under 4,000 K.
Red dwarfs are the most common types of known stars.

Red shifts

The shifting of an object's spectrum toward longer wavelenghts due to its motion away from an observer.

Runaway greenhouse effect

A condition in which water vapor raises environmental temperatures, which in turn causes more water evaporation and continues the cycle.

Saggitarius Dwarf Elliptical Galaxy

One of several satellite galaxies of the Milky Way. Some scientists believe that the Sagittarius Dwarf Elliptical Galaxy will eventually be absorbed by the Milky Way.
It is about 82,000 light years away.

Shoemaker-Levy 9

A comet discovered in 1993 by the American astronomers Carolyn and Eugene Shoemaker, and the Canadian astronomer David Levy.
It is best known for breaking up and crashing into Jupiter's surface in 1994.

Silicate

A common rocky material containing silicon, oxygen and one or more metals; the primary component of Earth's crust, as well as the crust of Mercury, Venus, Mars and some types of asteroids.

Skylab

NASA's first space station, launched into Earth orbit on May 14, 1973.
It functioned as a laboratory and short-term living quarters for three different teams of astronauts, before prematurely reentering Earth's atmosphere in 1979. Though most of Skylab burned up upon re-entry, some pieces survived and scattered through parts of Australia and the Indian Ocean.

Small Magellanic Cloud

A dwarf galaxy orbiting the Milky Way and containg several hundred million stars. It is located 210,000 light years away.

smog

A type of air pollution.

Solar and Heliospheric Observatory (SOHO)

An ESA spacecraft launched in 1995, tasked with the study of the outer layer of the Sun.

Solar corona

The upper atmosphere of the Sun, visible during a total Solar eclipse.

Solar eclipse

An event when the Moon passes between the Sun and the Earth, blocking our view of the Sun.

Solar prominences

Large plumes of plasma emitted from the Sun's surface, which extend into the Sun's corona before looping back.

Solar System

The eight planets and corresponding moons, as well as various astronomical objects all of which orbit the Sun.

Solar wind

Continuous streams of charged particles that are expelled from the Sun's corona at speeds of 400 kilometers per second.

Speed of light

The speed at which light travels in a vacuum, or 186,000 miles per second.

Stardust (spacecraft)

A probe launched in 1999 by NASA which collected samples from the coma of the comet Wild 2.

Subduction zones

Regions in the Earth's crust where one tectonic plate is being driven underneath another tectonic plate.

Sulfolobus Shibatae

S. Shibatae is a species of the genus Sulfolobus, thermoacidophiles (single-celled organisms that thrive in both acidic and extremely hot environments)that are found in volcanic hot springs.

Sulfuric acid

H2SO4 A highly corrosive, colorless mineral acid.

Sunspots

Temporary, dark spots found on the surface of the Sun, which are caused by intense magnetic activity.

Supergiants

Extremely large, massive and bright stars which have shorter life spans when compared to other stars.

Supernova

An explosion at the end of the life of a large star; it can be up to a billion times brighter than the Sun.

Taurus

One of the constellations of the zodiac, and home to the red giant star, Aldebaran.

Tectonic activity

The earthquakes and formation of mountains, volcanoes and continents that happen as a result of the motion of tectonic plates in relation to one another.

tectonic plates

Both the continental and oceanic plates that make up the Earth's crust.

Thebe

One of the moons of Jupiter, discovered by Stephen Synnott in 1979, from photographs taken by Voyager 1.
It has a size of 116 x 98 x 84 kilometers.

tidal forces

The flexing and pulling that occurs when the gravitational pull of a planet tugs on one of its satellites, causing the satellite's crust to flex up and down.

tidal locking

The locking of one astronomical body to another, so that one side of the smaller object is always facing the same way during its orbit around the larger object.

tidal resonance

The effect that happens when the rate of a wave traveling from one end of a bay to the other and back again, matches the rate from one high tide to the next one, resulting in much higher tides than would otherwise occur.

total eclipse

The complete obscuring of one celestian body by another.

totality

The period during an eclipse when the obscuring of one celestial body is total.

triple stars

A star system with three stars orbiting around one another. Also known as trinary stars.
Alpha Centauri is an example of a triple star system.

Tycho Brahe

Born in 1601, Tycho Brahe was a Danish astronomer known for his detailed observations of the sky.

Tycho (crater)

A crater close to the Moon's south pole, 86 kilometers in diameter, named after the astronomer Tycho Brahe.

Ulysses (spacecraft)

A joint project by NASA and ESA, the probe was launched in 1990 to study the Sun's magnetic field.
Communications with the spacecraft were terminated in 2009.

umbra

The darkest part of a shadow, as cast by a celestial body.
Also the dark middle region of a sunspot.

Ursa Major

A constellation in the northern sky also known as the Little Bear. Ursa Major is the location of the Big Dipper.

Ursa Minor

A constellation in the northern sky also known as the Little Bear. The star at the end of it's "tail" is Polaris, the north pole star.

Ultraviolet

A type of raditation that's invisible to the human eye, since its wavelenghts are shorter than those of visbile light.
Ultraviolet light can be found in sunlight, and is responsible for sunburns when exposed to it for too long.

Valles Marineris

A system of canyons on the surface of Mars that is 4,000 kilometers long by 2 to 7 kilometers deep.

Venera 7

Launched in 1970 by the USSR, Venera 7 was the first mission to land a capsule on another planet, when it parachuted a landing capsule on the planet Venus.

Venera 9

Launched on June 1975, the Soviet Venera 9 succeeded in landing another capsule on the surface of Venus, which sent back photos of the planet's surface.

Venus Express

A project of the ESA and launched on November 2005, Venus Express has been orbiting the planet Venus and sending back data since 2006.

4 Vesta

The second largest asteroid in the Solar System, it has a size of 578 x 560 x 458 kilometers.

Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Viking 1

A Mars mission launched on June 1976 by NASA, and consisting of both an orbiter meant for mapping of the planet, and a lander which took panoramic photographs of the planet and searched for evidence of life.

Virgo

One of the zodiac constellations and home of the stars Spica, Zavijava and Porrima.

Virgo cluster

A cluster of almost 2,000 galaxies, located in the constellation Virgo.

Voyager

A U.S. space program that was responsible for the design and launch of both Voyager 1 and Voyager 2 spacecraft.

Voyager 1

A spacecraft launched on September 5th, 1977 by NASA to explore the Solar System and fly by Jupiter and Saturn. In the event it is ever found by an alien civilization, Voyager 1 carries a gold-plated copper record with music, sounds, images and diagrams from Earth, designed in part by Carl Sagan and Frank Drake.
Currently, Voyager 1 is in the outer edges of the Solar System and is still in operation.

Voyager 2

The second half of the Voyager mission and launched by NASA on August 1977, Voyager 2 sent back data on previously unknown rings of Jupiter, detailed photographs of the Great Red Spot, close-up pictures of the moon Europa, and additional detailed photographs of the surface of Saturn. Voyager 2 also managed to continue on to the planet Uranus and gather more valuable information. Like its sibling, Voyager 1, Voyager 2 also carries a copy of the Golden Record.

white dwarf

A small, very dense star oject that cannot collapse into itself any further; one possible result for a low-mass star at the end of its life.

yellow dwarf

A type of star with surface temperatures between 5,300 and 6,000 K. When a yellow dwarf exhausts all of its hydrogen supply, it will become a red giant.