MISSION
Dawn Dictionary
A
Achondrite 
A meteorite consisting of igneous minerals and no chondrules, very similar to terrestrial igneous rocks
Albedo
The ratio of the amount of light reflected from a surface to the amount of incident light
Aperture
The effective diameter of the primary mirror or lens of a telescope
Aphelion
The point in a planetary orbit that is at the greatest distance from the Sun
Apparent Magnitude
The brightness of a star as it appears to the eye or to the telescope, as measured in units of magnitude—the brighter the star, the smaller the apparent magnitude.
Asteroid
(also called a “minor planet”) A small solar system object in orbit around the sun composed mostly of rock. Many of these objects orbit the sun between Mars and Jupiter. Their size can range anywhere from 100 meters in diameter to almost 1000 kilometers.
- Principal asteroids – Ceres, Pallas, Juno and Vesta
- C-type asteroids are carbon-rich, very dark, reflect only 3%-9% of sunlight.
- S-type asteroids are comprised of metallic nickel-iron mixed with iron- and magnesium-silicates.
- V-type asteroids contain more pyroxene than S-type asteroids.
Asteroid belt
A region of space lying between Mars (1.5 AU) and Jupiter (5.2 AU), where the great majority of the asteroids are found
Astronomical Unit (AU)
The mean distance between the Earth and the Sun: 149,598,500km; the preferred unit for distances within the Solar System
Axis of rotation
The theoretical straight line through a celestial body, around which it rotates
B
Bode’s Law
This law describes a mathematical method for calculating planetary distances which states that the distance to the nth planet is 0.4 + (0.3)n Astronomical Units. Bodes law works surprisingly well out to Uranus.
Brightness Magnitude
The apparent brightness of a star is called the apparent magnitude and that is what is measured by a telescope: how much energy the star puts into the telescope's collecting area per second.
Brightness
Refers to the amount of light coming from an object
C
Canon law
The body of ecclesiastical law
by which a Christian church is governed.
Celestial body
A solid object found in
space; in the heavens
Celestial Police
A group of astronomers
looking for Kepler’s missing planet between Jupiter
and Mars
Ceres
Largest of the known asteroids, and
the first to be discovered (by Piazzi in 1801)
Chondrite
A meteorite containing chondrules,
which are small, spherical silicate objects on the order of
a millimeter in size that formed in the solar nebula before
the asteroids were formed
Chondrules
A crystallized sphere of rocky material found in chondrite meteorites. Named after the Greek for seeds, they are essentially tiny igneous rocks that formed in the solar nebula.
Circumscribe
To draw a line around; to
encircle
Classical planets
Mercury, Venus, Mars,
Jupiter and Saturn are known as “the classical planets
Collodian
A viscous solution used in coating
photographic films; the wet collodion process produced plates
that had a much higher sensitivity than was previously available
Comet
A small solar system object orbiting
the Sun consisting of ice, dust and gas that form a coma and
sometimes a visible tail whenever they orbit close to the
Sun
Comet debris
Clumps of dust, ice and rocky
material that are released from comets as they approach the
sun
Concave
Hollowed or rounded inward like the inside of a bowl
Concave lens
A lens whose interior surface
in hollowed or curved inward, away from the viewpoint, making
the interior of the lens thinner than the outer edges
Convex
Curved or rounded outward like the exterior of a sphere or circle
Convex lens
A lens whose interior surface
is curved outward, toward viewpoint, making the interior of
the lens thicker than the outer edges
Convex - profile inversion
A modeling technique for producing a three-dimensional shape
from a two-dimension convex profile
Copernican system
A heliocentric
model of the universe; the hypothesis that the earth and the
other planets orbit the sun
Coulomb
A measure of the amount of electric current, being the quantity transferred in one second by a current of one ampere. 1 coulomb = 1 A s.
Crust
The outer part of a planet, moon, or asteroid composed essentially of crystalline rocks—generally the crustal composition is different from the bulk composition of the planet (adapted from Merriam-Webster.com).
D
Dawn Discovery Mission
The ninth of NASA’s
Discovery Program missions will investigate two of the largest protoplanets in the main asteroid belt, Vesta and Ceres.
Declination (DEC)
Declination is measured in degrees, and refers to how far above the imaginary"celestial equator" an object is (like latitude on the Earth).
E
Ecliptic
The mean plane of the Earth's orbit around the Sun
Elastic Collision
A collision between two
particles which conserves the total kinetic energy and momentum
of the system
Electromagnetic Radiation
"Waves"
of electrical and magnetic "disturbance", radiated
as visible light, radio waves, or any other manifestation
of the electromagnetic spectrum
Electron Volt (eV)
A unit of energy used
to indicate the energy of a charged particle. 1 eV is the
energy gained when an electron is accelerated by a potential
of one volt. 1 electron volt = 1.6 x 10-12 ergs
Elliptical
Shaped like an ellipse, a plane
curve in which the sum of the distances of each point along
its periphery from two points - its "foci" - are
equal
Emission spectrum
A spectrum of energy released from a source, usually in the form of electromagnetic radiation
Emit (also see Light)
To send forth or to send out electromagnetic radiation
Emulsion
A physical mixture of two immiscible liquids. One example is oil and vinegar in your salad dressing. Another example is suspending silver salts in a medium for coating plates and films.
Ephemeris (Ephemerides; plural)
A table that gives the positions of objects in the sky at various times
Epicycle
Circular orbit of a body round a point that is itself in a circular orbit round a parent body—such a system was formulated to explain some planetary orbits in the Solar System before they were known to be elliptical
Epithermal Neutron
A neutron that has undergone energy loss due to scattering collisions, but is not in thermalequilibrium with the regolith (E = ~0.3 eV to ~600 keV)
Evolutionary path
The path by which a body changes from one initial state to its final state. For example, many complex or differientiated asteroids develop from simpler states.
Exposure
To lay open to the influences of climate or other external forces
F
Fast Neutron
A neutron ejected at high kinetic energy in a nuclear reaction (E = ~103 eV to 6 MeV)
Fusion Crust
Fusion crust is the outer covering that a meteorite has acquired as a result of the melting of its surface layer as it passes through the atmosphere. The compression of the Earth's atmosphere heats the surface of the meteoroid to its melting point. Most of the melted material is ablated (removed): what remains resolidifies as the fusion crust. The thickness of these crusts can range from less than one millimeter up to several millimeters. Typically, the leading side of the meteoroid will have a thinner crust than the trailing side. Fusion crusts can be light or dark in color depending on the amount of iron in the meteorite minerals.
G
Gamma rays
Very energetic EMR photons with energies between 1 MeV–¬10 GeV
Inelastic collision; a collision between two particles in which part of their kinetic energy is transformed into another form of energy (gamma rays)—the total amount of energy remains the same
H
Heliocentric
Having the Sun at the center.
Hubble Space Telescope (HST)
NASA launched
the Hubble Space Telescope in 1990. It orbits around the Earth
every 97 minutes about 600 kilometers above the Earth, above
the distorting effects of the atmosphere. Hubble’s instruments
include cameras and spectrographs, using mirrors to focus
and magnify light.
I
Igneous
In the case of meteorites the term
“igneous” refers to a rock formed by solidification
of a molten rock or metal. Examples of igneous meteorites
include the iron meteorites, and basaltic meteorites (Howardites
and Eucrites) thought to come from the asteroid Vesta.
Impact basin (also impact crater)
A circular depression on the surface of a planet,
moon, asteroid, or other celestial body. Craters are typically
caused by meteorite impacts. In complex craters formed by large impacts, a central peak or peak ring is caused by rebounding crustal rock after the impact. In the center of some impact craters on Earth,
a crater lake accumulates; but some crater lakes occur in volcanic craters, as well.
Inclination
In astronomy,
the angle between one plane and another. The (equatorial)
inclination of a planet is the angle between the plane of
its equator and that of its orbit. The inclination of the
orbit of a planet in the Solar System other than Earth is
the angle between the plane of that orbit and the ecliptic.
Inelastic Collision
A reaction involving a change in the kinetic energy of the system, as in ionization, excitation, or capture; or a process which changes the energy level of the system.
Ion
A charged particle consisting of an
atom, or group of atoms, that has either lost or gained electrons.
Ionization
Loss or gain by an atom of one
or more electrons, by which process the atom becomes an ion
and instead of being neutral, has a charge: positive if it
has lost an electron, negative if it has gained one.
Ion propulsion
A system in which the atoms of the propellant are given an electrical charge by removing electrons. The charged atoms—ions—are then accelerated with electric or magnetic fields and emitted at very high velocity, imparting a thrust to the spacecraft. The high velocity of the propellant makes this technology very efficient. On Dawn, xenon atoms are ionized and accelerated with an electric field which is produced with a voltage between two grids. This design is inherited directly from Deep Space 1 (DS1), which was the first interplanetary mission to use ion propulsion.
IPS
Acronymn for Ion Propulsion System. (See ion jet propulsion above.)
Inscribe
To draw on figure within another
so as to have as many incidences as possible.
L
Light
The radiant energy that enables organs
of vision to perform the function of sight—more accurately
called luminous energy. (see also Electromagnetic Radiation).
- Emitted - An emanation of light from a light-giving
body, such as the Sun
- Infrared light - Electromagnetic radiation with wavelengths
too long to be detectable by the human eye, yet able to be seen by an infrared camera.
- Reflected Light - Light that is purely returned back from or bounced off an object.
- Visible Light - Electromagnetic radiation with wavelengths
of or close to those detectable by the human eye.
Light Curve
A plot of the amount of light
detected from an object (i.e., the apparent magnitude) as a
function of time. Light curves provide evidence of eclipsing
binaries, variable stars, and track the progress of nova and
supernova explosions. Asteroid light curves can give evidence of the asteroid's shape, or how its surface properties vary.
M
Magnification
The effect of an optical
system on the apparent angular size of an object—an increase
in angular size occurs if the magnification factor is greater
than 1
Magma
Molten rock material
within a melted planet or asteroid from which igneous rock
results by cooling (adapted from Merriam-Webster.com)
Magnitude
An astronomical unit of brightness—originally corresponding to the eye's response to starlight—the magnitude system is logarithmic, with 5 magnitudes corresponding
to a factor of 100 in brightness. To further confuse things
larger magnitudes correspond to fainter objects.
Mantle
The part of a planet or asteroid between the crust and the core
Metamorphic
A metamorphic rock contains minerals that have recrystallized after melting. In meteorites, the melting may occur due to internal heat on the parent body—heat from radiogenic decay—or heat from impacts.
Meteor
The flash and trail of light that we see in the night sky caused by a meteoroid passing through the atmosphere
Meteorite
An object that passes through the Earth's atmosphere and is too large to be destroyed before it hits the surface—meteorites may in some way be connected with asteroids.
Meteoroid
An interplanetary piece of matter larger than dust, but smaller than an asteroid or dwarf planet
Minor planet
(see Asteroid) Technically, anything that is not classified as a planet is a minor planet, so any small body in the solar system that primarily orbits the Sun that is not characterized as a satellite of another planet. Pluto is a minor planet, for example.
N
Nebulosity
A hazy, cloudy, or misty characteristic of matter in a gaseous or finely divided state
Neutron capture
A process in which a neutron is absorbed by a nucleus to produce an excited nucleus that transitions to ground state by emission of one or more gamma rays
O
Observatory
A building equipped for observation of natural phenomena, as in meteorology or astronomy
Opposition
A configuration of the Sun, Earth and a planet or asteroid in which the apparent geocentric longitude of the planet or asteroid differs by 180 degrees from the apparent geocentric longitude of the Sun. During opposition, the planet is closest to full for that particular orbit.
P
Patent
A writing securing to an inventor the exclusive right to make, use, and vend his invention
Period of revolution
The interval of time required to complete one revolution in an orbit
Photochemical
Materials in which the absorption of light leads to a chemical reaction
Photographic plate
The flat surface on which the emulsion containing light-sensitive chemicals is placed; after exposing to light, the emulsion forms a negative of the object photographed.
Photometry
The measurement of light. Specifically
refers to the procedure of highly accurate measuring of the
apparent magnitudes of astronomical objects. In general, astronomers
measure only a portion of the wavelength spectrum when they
do photometry. Different types of photometry are defined by
the portion of the wavelength that they examine. Differential
photometry, or "UBV Photometry", measures the light
within three standard regions defined by filters. These are
Ultraviolet, Blue and Visual (hence UBV). There are many different
photometry systems and standards.
Photomultiplier tube
A vacuum encapsulated
photocathode from which electrons are ejected by the photoelectric
effect followed by multiple cathodes from which many additional
electrons are emitted in a cascade—when finally collected,
the original single electron may have generated a pulse of
over one million electrons; first used in astronomy in the
early 1950s in a process known as differential photometry
Planetary orbit
The path in space followed by a planet
Planet
A large object formed from the solar nebula; the disk-shaped cloud of gas and dust surrounding a protostar. The classification of a planet by type (such as giant, dwarf, terrestrial, jovian, super Earth, etc.), depends on the body's intrinsic and orbital properties.
Power
The magnifying capacity of a lens, expressed as the number of times it multiplies the diameter of an object
Protoplanets
Early stage in the formation of planets according to the theory by which planetary systems evolve through the condensation of gas clouds surrounding a young star
Ptolemaic system or Ptolemaic Model of the Universe
A geocentric model in which the Earth remained stationary as the other planets the Sun, the Moon and the stars orbited it on their spheres— was eventually replaced by the Copernican model
Pyroxene
A common metasilicate, chiefly of calcium and magnesium, usually in short, thick, prismatic crystals; next to feldspar the most frequent constituent of igneous rocks
R
Reciprocity failure
The tendency for film emulsions to suffer a rapid fall-off in their ability to gather data after an initial surge of light
Reflection
The return of light or sound waves from a surface
Reflecting telescope
Telescope that uses mirrors to magnify and focus an image
Refraction
The bending of light as it passes from one medium to another
Refracting Telescope
Telescope that uses lenses to magnify and focus an image onto an eyepiece
Regmaglypts
Thumbprint-like indentations that are caused by parts of the meteorite melting and being sloughed off in its descent through Earth’s atmosphere
Regolith
The layer of rocky or icy debris and dust made by meteoritic impact that forms the uppermost surface of planets, moons and asteroids
Retina
The sensitive membrane of specialized cells in the eye which receives the image formed by the lens and is connected with the brain by the optic nerve
Right ascension (RA)
Right ascension is measured in hours of time. It is similar to longitude on the Earth. Astronomers have chosen the Vernal Equinox to define the starting point for the measurement of right ascension. The Vernal Equinox is the point where the Sun appears to cross the Celestial Equator at the beginning of spring. It is therefore one of the two points where the Ecliptic intersects the Celestial Equator.
Rotation
Of a single body
in space, spinning on an axis; of a planetary system, rotation
is generally planar in relation to the parent star
S
Scintillator
A phosphor-containing radiation detector that absorbs a photon or ionizing particle
Semiconductor
A substance or material, typically crystalline, that conducts electricity better than an insulator, but not as well as a conductor, because it only allows current to flow under certain condictions. Common semiconductors are silicon, germanium, and gallium arsenide.
Semi-major axis
Half the length of the major axis of an ellipse; a standard element used to describe an elliptical orbit
Sensitivity
The capacity to respond to stimulation
Serendipity
Finding without seeking
Silver bromide
A yellowish, odorless powder that darkens on exposure to light; is used in photographic colloids
Silver iodide
A light yellow, odorless power that slowly darkens by light; is used in photographic colloids
Solar Nebula
The cloud of gas and dust that condensed and accumulated to form the Solar System.
Solar System
The complex of planets, asteroids, comets, and debris gravitationally bound to the Sun and including the particles and fields emitted from the sun and interacting with its components
Spacecraft
A vehicle that can travel in outer space
Speckle interferometry
A process that uses ground-based telescopes and computer technology to make highly detailed or high-resolution images of asteroids by clustering together loads of tiny “specks” to form a clearer picture
Spectra
The energies of the photons emitted or absorbed by an atom or compound are distinct. Photon energies are directly related to their frequencies and thus wavelengths, which dictate the colors in the spectrum. By observing the wavelength or frequency of a reflected or emitted photon, it is possible to determine which atoms or compounds comprise the body being observed. Spectra can be detected from the light reaching us from stars and planets, near or very distant, enabling us to identify the composition of the observed object.
Spectroscope
An optical
instrument used for producing and observing spectra of light
or other radiation
Spectroscopy
Spectroscopy is the study
of the detailed features of a body's spectrum, accomplished by measuring
the intensity of light emitted or reflected at as many different wavelengths
as possible. The resulting spectrum of light allows us to
locate emission or absorption lines which determine the object's composition, temperature, and properties—and for a distant, fast-moving object, even its velocity relative to
Earth.
Sublimation
The process by which a substance transitions directly from the solid to the gas phase. By comparison, evaporation is the process by which a substance transitions from a liquid to a gas phase.
T
Telescope
An optical instrument for making distant objects appear closer or larger
Theory
In science a theory is a verified hypothesis applicable to many related phenomena.
Thermal Neutron
A neutron produced by fission and slowed by a moderator, so that it is in thermal equilibrium with its surrounding medium; (E< ~0.3 eV)
Titius-Bode Law
The Titius-Bode Rule was first devised in 1772 and comprised the series 0 + 4/10, 3 + 4/10, 6 + 4/10, 12 + 4/10, 24 + 4/10 and so on. It was found to describe fairly accurately the distance in astronomical units of the then known planets from the Sun.
