A meteorite with embedded pebble-sized granules that contain
significant quantities of organic (complex carbon-rich) matter.
A type of reflecting telescope whose eyepiece is located behind the primary mirror. The primary mirror is cast with a hole in the center. When light enters the telescope, it reflects from the primary mirror to the secondary mirror. The secondary mirror reflects the light back through the hole in the primary mirror to the eyepiece.
Of or relating to the sky or visible objects in the sky, like the Moon, Sun, planets, comets, asteroids, stars, and galaxies.
An object in the sky – examples include the Moon, the Sun, planets, comets, asteroids, stars, and galaxies.
An imaginary sphere encompassing the Earth that represents
the sky. Astronomers chart the sky using the celestial coordinates of the sphere
to locate objects in the cosmos. This sphere is divided into 88 sections called
constellations. Objects are sometimes named for the major constellation in which
Celsius (Centigrade) Temperature Scale
A temperature scale on which the freezing point of water
is 0° C and the boiling point is 100° C.
A type of pulsating star whose light and energy output
vary noticeably over a set period of time. The time period over which the star
varies is directly related to its light output or luminosity, making these stars
useful standard candles for measuring intergalactic distances.
Chandra X-Ray Observatory
A space-based X-ray observatory; also known as the Advanced
X-ray Astrophysics Facility (AXAF). Chandra is designed to observe X-rays from
high-energy regions of the universe, such as hot gas in the remnants of exploded
stars. The satellite was launched and deployed in July 1999.
Charge-coupled device (CCD)
An electronic detector that records visible light from stars and galaxies to make photographs. These detectors are very sensitive to the extremely faint light of distant galaxies. They can see objects that are 1,000 million times fainter than the eye can see. CCDs are electronic circuits composed of light-sensitive picture elements (pixels), tiny cells that, placed together, resemble mesh on a screen door. The same CCD technology is used in digital cameras.
A pure substance consisting of atoms or ions of two or
more different elements. The elements are in definite proportions. A chemical
compound usually possesses properties unlike those of its constituent elements.
For example, table salt (the common name for sodium chloride) is a chemical
compound made up of the elements chlorine and sodium.
The chemical (i.e., pre-biological) changes that transformed
simple atoms and molecules into the more complex chemicals needed for the origin
of life. For example, hydrogen atoms in the cores of stars combine through nuclear
fusion to form the heavier element helium.
Visible light is made of different
colors. When visible light passes through a glass lens or a
prism, it gets dispersed, or split, into its many colors. A
lens focuses each color at a different point, causing a
fringe of color to appear around bright objects.
Looking at only red and blue light:
The middle layer of the solar atmosphere between the photosphere
and the corona. The chromosphere is roughly 10,000 kilometers (6,200 miles)
thick and is composed primarily of hydrogen. It varies in temperature from below
10,000 Kelvin (18,000° F) to over 100,000 Kelvin (180,000° F).
A geometric model of the universe in which the overall
structure of the universe closes upon itself like the surface of a sphere. The
rules of geometry in a closed universe are like those that would apply on the
surface of a sphere.
A system of two moveable mirrors used in solar telescopes. The mirrors follow the Sun and keep its image in the same location as Earth rotates.
The area of a telescope’s primary light-collecting
mirror. A telescope’s light-gathering power rises with an increase in its
A galactic “car wreck” in which two galaxies
pass close enough to gravitationally disrupt each other’s shape. The collision
rips streamers of stars from the galaxies, fuels an explosion of star birth,
and can ultimately result in both galaxies merging into one.
An event involving a collision of objects; for example,
the excitation of a hydrogen atom when it is hit by an electron.
The visual perception of light that enables human eyes
to differentiate between wavelengths of the visible spectrum, with the longest
wavelengths appearing red and the shortest appearing blue or violet.
The cloud of gas and dust that forms around a comet's nucleus. This cloud is created when the solar wind strikes the surface of the nucleus.
A ball of rock and ice, often referred to as a “dirty
snowball.” Typically a few kilometers in diameter, comets orbit the Sun
in paths that either allow them to pass by the Sun only once or that repeatedly
bring them through the solar system (as in the 76-year orbit of Halley's Comet).
A comet’s “signature” long, glowing tail is formed when the Sun’s
heat warms the coma or nucleus, which releases vapors into space.
The core of a comet, made up of ice, dirt, and rock.
Comet Shoemaker-Levy 9 (SL-9)
A comet that became gravitationally bound to Jupiter,
colliding with the planet in July 1994. Prior to entering the planet’s atmosphere,
the comet broke into several distinct pieces, each with a separate coma and
A tail is made up of dust and gas from a comet’s coma. A tail forms when the solar wind separates dust and gas from the coma, pushing it outward and away from the Sun in either a slightly curved path (for dust) or a straight path (for gas).
Compton Gamma-Ray Observatory (CGRO)
A space-based observatory that collected high-energy gamma-ray
light from celestial objects. The Compton satellite consisted of the BATSE,
COMPTEL, EGRET, and OSSE instruments. Astronauts aboard the space shuttle Atlantis
deployed the CGRO into low-Earth orbit in April 1991. The satellite plunged
into the Pacific Ocean in June 2000.
Concave vs. convex
Conservation of Energy And Mass
A fundamental law of physics, which states that the total
amount of mass and energy in the universe remains unchanged. However, mass can
be converted to energy, and vice versa.
A geometric pattern of bright stars that appears grouped
in the sky. Ancient observers named many constellations after gods, heroes,
animals, and mythological beings. Leo (the Lion) is one example of the 88 constellations.
The transfer of heat through a liquid or gas caused by
the physical upwelling of hot matter. The heat transfer results in the circulation
of currents from lower, hotter regions to higher, cooler regions. An everyday
example of this process is boiling water. Convection occurs in the Sun and other
The region below a star's surface where energy flows outward
by the rising of hot gas known as convection.
The central region of a planet, star, or galaxy.
The outermost layer of the atmosphere of a star, including
the Sun. The corona is visible during a solar eclipse or when special adapters
or filters are attached to a telescope to block the light from the star’s
central region. The gaseous corona extends millions of kilometers from the star’s
surface and has a temperature in the millions of degrees.
Regions in the corona from which the high-speed solar
wind is known to originate. Coronal holes, usually found near the Sun's poles,
are large regions in the corona that are less dense and cooler than the surrounding
Corrective Optics Space Telescope Axial Replacement (COSTAR)
An apparatus installed during the 1993 First Servicing Mission. By placing small and carefully designed mirrors in the telescope, COSTAR successfully improved restored Hubble’s vision to its original design goals. All the new instruments installed during the servicing missions have internal corrections for spherical aberration and do not require the services of COSTAR. Hubble’s last original instrument, the Faint Object Camera, was replaced by the Advanced Camera for Surveys during SM3B. COSTAR was replaced by the Cosmic Origins Spectrograph during Servicing Mission 4 and returned to Earth in the space shuttle.
The relative proportions of chemical elements in the Sun,
the solar system, and the local region of the Milky Way galaxy. These proportions
are determined by studies of the spectral lines in astronomical objects and
are averaged for many stars in our cosmic neighborhood. For example, for every
million hydrogen atoms in an average star like our Sun, there are 98,000 helium
atoms, 360 carbon atoms, 110 nitrogen atoms, 850 oxygen atoms, and so on.
Cosmic Microwave Background
Radiative energy filling the universe that is believed
to be the radiation remaining from the Big Bang. It is sometimes called the
“primal glow.” This radiation is strongest in the microwave part of
the spectrum but has also been detected at radio and infrared wavelengths. The
intensity of the cosmic microwave background from every part of the sky is almost
exactly the same.
Cosmic Origins Spectrograph (COS)
A spectrograph that detects ultraviolet light. A spectrograph works by breaking up light from an object into its individual wavelengths so that its composition, temperature, motion, and other chemical and physical properties can be analyzed. COS will study the structure of the universe and how galaxies, stars and planets formed and evolved. Astronauts installed COS during SM4.
High-energy atomic particles that travel through space
at speeds close to the speed of light; also known as cosmic-ray particles.
Cosmic background radiation
Electromagnetic energy filling the universe that is believed to be the radiation remaining from the Big Bang. It is sometimes called the “primal glow.” This radiation is strongest in the microwave part of the spectrum but has also been detected at radio and infrared wavelengths. The intensity of the cosmic microwave background from every part of the sky is almost exactly the same.
This principle states that the distribution of matter
across very large distances is the same everywhere in the universe and that the universe
looks the same in all directions. According to this principle, our view of the
universe is like the view from a boat on an ocean, which is essentially the
same for any other person on any other boat on any other ocean. Measurements
of matter and energy in the universe on the largest observable scales support
the cosmological principle.
The investigation of the origin, structure, and development
of the universe, including how energy, forces, and matter interact on a cosmic
A bowl-shaped depression caused by a comet or meteorite
colliding with the surface of a planet, moon, or asteroid. On geologically active
moons and planets (like Earth), craters can result from volcanic activity.
The minimum average density that matter in the universe
would need in order for its gravitational pull to slow the universe’s
expansion to a halt.
Originally the main material used to make flat planes of glass for windows, it is composed of soda-lime glass. It can be used to make lenses and prisms. Crown glass bends and disperses, or spreads out, light less than flint glass.
Dark Dust Cloud
A region of interstellar space that contains a rich concentration
of gas and dust. Such a cloud is often irregular in shape but sometimes has
a well-defined edge. Visible light cannot pass through these clouds, so they
obscure the light from stars beyond them.
Matter that is too dim to be detected by telescopes. Astronomers
infer its existence by measuring its gravitational influence. Dark matter makes
up most of the total mass of the universe.
A mysterious force that seems to work opposite to that of gravity and makes the universe expand at a faster pace.
One of two celestial coordinates required to locate an
astronomical object, such as a star, on the celestial sphere. Declination is
the measure of angular distance of a celestial object above or below the celestial
equator and is comparable to latitude. To familiarize yourself with declination,
hold out your arm in the direction of the North Star (Polaris). You are now
pointing at plus 90 degrees declination. Move your arm downward by 90 degrees.
You are now pointing at 0 degrees declination.
Degree of Arc
One degree of arc is 1/360 of a full circle. The apparent
sizes of objects as seen from Earth can be measured in degrees of arc. The angular
diameter of the full moon or the Sun as seen from Earth is one-half of a degree.
The ratio of the mass of an object to its volume. For
example, water has a density of one gram of mass for every milliliter of volume.
A device used to measure the amount of electromagnetic radiation emitted by celestial objects. Frequently, detectors are used to sense light that is not visible.
A special form of hydrogen (an isotope called “heavy
hydrogen”) that has a neutron as well as a proton in its nucleus.
The distance from one side of a circle to the other measured through the center. For telescopes, the diameter of a lens or mirror is measured from one side to the opposite side, passing through the center.
The separation of heavy matter from light matter, thus
causing a variation in density and composition. Differentiation occurs in an
object like a planet as gravity draws heavier material toward the planet’s
center and lighter material rises to the surface.
A device that splits light into its component parts or
spectrum. A diffraction grating often consists of a mirror with thousands of
closely spaced parallel lines, which spread out the light into parallel bands
of colors or distinct fine lines or bars.
A visible image that is recorded by an electronic detector
and subdivided into small picture elements (pixels). Each element is assigned
a number that corresponds to the brightness recorded at its physical location
on the detector. Computer software converts the numerical information into a
visual image. The Hubble Space Telescope records digital images.
Visible light is actually made up of different colors. Each color bends by a different amount when refracted by glass. That’s why visible light is split, or dispersed, into different colors when it passes through a lens or prism. Shorter wavelengths, like purple and blue light, bend the most. Longer wavelengths, like red and orange light, bend the least.
The change in the wavelength of sound or light waves caused
when the object emitting the waves moves toward or away from the observer; also
called Doppler Shift. In sound, the Doppler Effect causes a shift in sound frequency
or pitch (for example, the change in pitch noted as an ambulance passes). In
light, an object’s visible color is altered and its spectrum is shifted toward
the blue region of the spectrum for objects moving toward the observer and toward
the red for objects moving away.
A system of two stars that are gravitationally bound to each other. They orbit each other around a common center. They can also be called binary stars.
A relatively small galaxy. The Large and Small Magellanic
Clouds, visible in the Southern Hemisphere, are two dwarf irregular galaxies
that are neighbors of the Milky Way.
A celestial body within the solar system that shares the characteristics of planets. It orbits the Sun, is not a moon, and has a spherical or nearly spherical shape. Unlike a planet, however, a dwarf planet has not cleared away any loose cosmic rubble from its orbit. Dwarf planets include Ceres, Pluto, and Eris.