Radio Emission Produced by cold, low-density
hydrogen in interstellar space.
The Absolute Magnitude we would observe if
we could detect all wavelengths
Intrinsic brightness of a star; the apparent
visual magnitude the star would have if it were 10 Parsecs away from earth.
The lowest possible temperature. The temperature
at which particles in a material, atoms or molecules, contain no energy
of motion that can be extracted from a body.
A dark line in a spectrum. Produced by the
absence of photons absorbed by atoms or molecules.
A Spectrum that contains absorption lines.
A change in velocity
Falling objects fall with an increasing acceleration
of 9.8 meters per second per second.
The sticking together of solid particles
to form a larger particle.
The whirling disk of gas that forms around
a compact object such as a white dwarf, neutron star or black hole as
matter is drawn in
A telescope lens composed of two lenses ground
from different types of glass and designed to bring two selected colors
to the same focus and correct for chromatic aberration
A galaxy that is a source of excess radiation,
usually radio waves, X rays, gamma rays or some combination
The central energy source of an active galaxy
Optical elements whose position or shape
is continuously controlled by computers
Computer controlled telescope mirrors that
can adjust for some changes in seeing conditions
A telescope mounting capable of motion parallel
to and perpendicular to the horizon
1 x 10 -10 meters (used to measure wavelengths)
Measure of the rotation of the body around
A type of total eclipse in which the moon
is too far from the earth to totally cover the suns surface. A ring of
the photosphere surrounds the moon during mideclipse. The corona is not
visible and neither are the prominence because of the glare from the photosphere.
Rock of aluminum and calcium silicates found
in the lunar highlands.
Point in the earth's orbit where the earth
is farthest away from the Sun (summer for us)
Orbital point of greatest distance from the
The Orbit of one star in a visual binary
with respect to the other star as seen from earth
Is the magnitude of the stars without compensating
for their distance from Earth.
On Venus, one of a number of round networks
of fractures in the crust, resembles spider webs.
The study of astronomy by ancient peoples
Groups of widely scattered stars (10 - 1000)
moving together through space; not gravitationally bound to clusters.
Named group for stars not identified as constellations
Small Rocky worlds, most of which lie between
Mars and Jupiter in the asteroid belt.
A binary star identified by its irregular
Is the average distance from the Earth to
the Sun. 1 AU = 93 million miles or 1.5 X 1011 meters or 1.5 X 109 km.
Is the study of the universe
Wavelength regions in which our atmosphere
is transparent - at visual wavelengths, infrared and radio.
The glowing light display that results when
a planet's magnetic field guides charged particles toward the north and
south magnetic poles, where they strike the upper atmosphere and excite
atoms to emit photons.
The place where the Sun crosses the celestial
equator heading south.
Short Period variables stars that do not
lie in the instability strip
A spiral galaxy with an elongated nuclei
resembling a bar from which the arm originate.
Dark, igneous rock characteristic of solidified
Dark bands of clouds that circle Jupiter
parallel to its equator; generally red, brown, or blue-green; believed
to be regions of descending gas.
The theory that the universe began with a
violent explosion from which the expanding universe of galaxies formed.
Pairs of stars that orbit around their common
center of mass
The energy needed to pull an electron away
from its atom.
Opposite directed jets of gas ejected by
some protostellar objects.
Objects resemble quasars; thought to highly
luminous cores of distant galaxies.
Radiation emitted by a hypothetical perfect
radiator. The spectrum is continuous, and the wavelength of maximum emission
depends only on the body's temperature.
The end state of a white dwarf that has cooled
to a low temperature
A mass that has collapsed to such a small
volume that its gravity prevents the escape of all radiation; also, the
volume of space from which the radiation may not escape.
Blue shifts: Shorting of wavelengths of observed
light when an object in moving toward the observer. Red Shifts: Lengthening
of wavelengths of light as the object moves away from the observer.
Small, dark clouds only about 1 light year
in diameter that contain 10-1000 solar masses of gas and dust. Believed
to be related to star formation.
The boundary between the undisturbed solar
wind and the region being deflected around the planet or comet
A rock composed of fragments of earlier rocks
A very cool, low luminosity star whose mass
is not sufficient to ignite nuclear fusion.
A source of bursts of X-rays or in some cases,
gamma rays; believed to be associated with neutron stars.
The theory that the moon formed elsewhere
in the solar system and was later captured by the earth.
The explosive ignition of carbon burning
in some giant stars. A possible cause of some supernova explosions
A reflecting telescope in which the secondary
mirror reflects light back down the tube through a hole in the center
of the primary mirror
An imaginary line around the sky which is
directly above the earth's equator.
Imaginary sphere surrounding the Earth to
which the stars, planets, Sun and moon seem to be attached.
Two bodies revolve around a common center,
called the balance point of the system.
Variable stars with a period of 1-60 days.
Their period is related to luminosity.
The maximum mass of a white dwarf, about
1.4 solar masses. A white dwarf of greater mass can not support itself
and will collapse.
A CCD is an electronic device consisting
of an array of photosensitive elements, used to record images.
A line layer of gas just above the photosphere
of the sun, it is often marked by solar eruptions called solar flares
A distortion found in refracting telescopes
because lenses focus different colors at slightly different distances.
Images are consequently surrounded by color fringes
The lateral velocity an object must have
to remain in orbit
Constellations which appear around the celestial
poles, which never seem to rise or set.
A circular orbit, one which returns back
A model universe in which the average density
is great enough to stop the expansion and make the universe contract.
The method of determining the masses of galaxies
in a cluster.
A series of nuclear reactions that use carbon
as a catalyst to combine four hydrogen atoms to make one helium atom plus
energy; effective in stars more massive than the sun.
The theory that the moon and the earth formed
The cloud of gas and dust around a contracting
protostar that conceals it at visible wavelengths.
The smearing out of a spectrum line because
of collisions among the atoms of the gas.
A numerical measure of the color of a star.
One of the small, icy bodies that orbit the
sun and produce tails of gas and dust when they near the sun.
A star that has collapsed to form a white
dwarf, neutron star or black hole.
The study of planets by comparing the characteristics
of different examples.
The sequence in which different materials
condense from the solar nebula as we move outward from the sun.
Apparent arrangement of stars, usually named
after ancient gods, heroes, animals or mythological beings.
One of the basic laws of stellar structure,
The amount of energy flowing out of the top of a shell must equal the
amount coming in at the bottom plus whatever energy is generated within
One of the basic laws of stellar structure.
The total mass of the star must equal the sum of the masses of the shells,
and the mass must be distributed smoothly throughout the star.
A spectrum in which there are no absorption
or emission lines.
The faint outer atmosphere of the Sun that
is exposed during a total solar eclipse.
On Venus, circular features, not caused by
impacts, they are domed plains caused by the rising plumes of molten rock
A telescope designed to photograph the inner
corona of the sun.
An Area of the solar surface that is dark
at X-ray wavelengths; thought to be associated with divergent magnetic
fields and the source of the solar wind.
Atomic nuclei that enter earth's atmosphere
at nearly the speed of light. Some originate in solar flares, and some
may come from supernova explosions, but their true nature is not well
The assumption that any observer in any galaxy
sees the same general features of the universe.
The study of the nature, origin and evolution
of the universe.
The focal arrangement of a reflecting telescope
in which mirrors direct the light o a fixed focus beyond the bounds of
the telescope's movement. typically in a separate room, used primarily
The average density of the universe needed
to make its curvature flat.
The temperature and pressure at which vapor
and liquid phases of a material have the same density.
A nebula consisting of dust and gas blocking
our view of more distant stars.
Radio signals from Jupiter with wavelengths
Extremely high density matter in which pressure
no longer depends on temperature due to the quantum mechanical effects.
Theory proposed to account for spiral arms
as compressions of the interstellar medium in the disk of the galaxy.
Just as totality begins during a solar eclipse
a small portion of the Suns photosphere can peak out from behind the moon
through a valley at the edge of the lunar disk. It is not visible during
every solar eclipse.
The rotation of a body in which different
parts of the body have different periods of rotation. This is true of
the sun, Jovian planets, and the disk of the galaxy.
The separation of planetary material according
Blurred fringe surrounding and image caused
by wave properties of light. because of this no image detail smaller than
the fringe can be seen
All material confined to the plane of the
Objects whose luminosities or diameters are
known; used to find the distance to a star cluster or galaxy.
The difference between the apparent and absolute
magnitude of a star. A measure of how far away the star is.
The apparent daily rotation of the sky.
The smearing of spectral lines because of
the motion of atoms in the gas.
A change in the wavelength of radiation due
to relative radial motion of the source and the observer.
A method of finding the masses of galaxies
from orbiting pairs of galaxies.
A pair of stars close together in the sky.
Not all double stars are necessarily in orbit around each other.
The theory that double radio lobes are produced
by pairs of jets emitted in opposite directions from the centers of active
A spectroscopic binary star in which spectral
lines from both stars are visible in the spectrum
A star that undergoes novalike explosions
every few days or weeks; believed to be associated with mass transfer
onto a white dwarf in a binary system.
The theory that the earth's magnetic field
is generated in the conducting material of its molten core.
An offcenter circular path
Is the season when the Sun is close enough
to a node for an eclipse to occur, An eclipse season is 32 days. Any new
moon during this period will cause a solar eclipse. For Lunar eclipses
the period is shorter only about 22 days. A full moon occurring during
this time will cause a lunar eclipse.
The 346.62 days it takes the sun to return
to a node
A binary star system in which the stars eclipse
The apparent path of the Sun around the Sky.
Pulverized rock scattered by meteorite impacts
on a planetary surface.
The UV radiation produced in the upper atmosphere
of Jupiter, Saturn, Uranus by high-energy particles in the planet's magnetosphere.
Changing electric and magnetic fields that
travel through space and transfer energy from one place to another - light,
radio waves and magnetism
A low mass atomic particles carrying a negative
A closed curve enclosing two points (foci)
such that the total distance from one focus to any other point on the
curve back to the other focus equals a constant.
A galaxy that is round or elliptical in outline.
It contains little gas and dust, no disk or spiral arms, and a few hot,
A bright line in a spectrum caused by the
emission of photons from atoms.
A cloud of gas excited by UV wavelengths
of hot stars,
A spectrum containing emission lines
One of a number of states an electron may
occupy in an atom, depending on its binding energy.
An object that releases energy. Commonly
used to refer to the source of energy in active galactic nuclei
An attempt to explain the retrograde loop
in the earth centered universe, by attaching the planets to epicycles
and having them revolve around that, and in turn around the earth.
Ptolemy placed the earth offcenter and the
opposite point from the deferent on this off center circle is called the
A telescope mounting that allows motion parallel
to and perpendicular to the celestial equator.
The region surrounding a rotating black hole
within one could not resist being dragged around the black hole. It is
possible for a particle to escape from the erosphere and extract energy
from the black hole.
The velocity needed to escape from the surface
of a body
The boundary of the region of a black hole
from which no radiation may escape. No event that occurs with the event
horizon is visible to a distant observer.
An atom in which an electron has moved from
a lower to higher orbit.
The dimming of light by intervening material;
commonly, dimming by the interstellar medium.
A short focal length lens used to enlarge
the image in a telescope; the lens nearest the eye
A graphical representation of data in which
an images is colored to reveal additional detail
A way of explaining action at a distance.
An instrument that permits precise measurements
at the telescope of the position of visual binary stars and similar objects.
A photograph (usually of the sun) taken in
the light of a specific region of the spectrum - e.g., an H-alpha filtergram.
The theory that the moon formed by breaking
away from the earth.
A violent eruption on the sun's surface.
The emission spectrum of the chromosphere
that is visible for the few seconds during a total solar eclipse when
the moon has covered the photosphere but has not covered the chromosphere.
A model of the universe in which space-time
is not curved.
In cosmology the circumstance that the early
universe must have contained almost exactly the right amount of matter
to close the space-time (to make space-time flat)
Woolly, fluffy; used to refer to certain
galaxies that have a woolly appearance.
A distance from a lens to a point where it
focuses parallel rays of light.
The points around which an ellipse is drawn
The optical property of finely divided particles
to preferentially direct light in the original direction of the light's
The number of times a given event occurs
in a given time; for a wave the number of cycles that pass the observer
in one second
The theory that large galaxies absorb smaller
The low-density extensions of the halo of
a galaxy; now suspected to extend many times the visible diameter of the
The four largest moons of Jupiter, named
after their discoverer Galileo.
A unit used to measure the strength of a
Observers can not distinguish locally between
inertial forces due to acceleration and uniform gravitational forces due
to the presence of a massive body. Mass tells space-time how to curve,
and the curvature of space-time (gravity) tells mass how to accelerate
Aristotle believed the universe was divided
into two parts, the earth corrupt and the heavens perfect and immutable.
The geocentric universe described the universe with the earth at the center.
Very large, cool clouds of dense gas in which
Large, cool, highly luminous stars in the
upper right of the H-R diagram. Typically 10-100 times the diameter of
Time when glaciers advance and engulf huge
sheets of land
A sudden change in the period of a pulsar.
A star cluster containing 50,000 to 1 million
stars in a sphere about 75 light years in diameter; generally old metal
poor and found in the spherical component of the galaxy.
A linear feature on a planetary surface caused
by the faulting and sinking of portions of the crust.
The fine structure visible on the solar surface
caused by rising currents of hot gas and sinking currents of cool gas
below the surface.
Material onto which microscopic parallel
lines are inscribed. used to create a spectrum of colors from light
The focusing of light from a distant galaxy
or quasar by an intervening galaxy to produce multiple images of the distant
A lengthening of the wavelength of a photon
due to its escape from a gravitational field.
A transport of energy by the motion of waves
in a gravitational field; predicted by general relativity
The process by which a carbon dioxide atmosphere
traps heat and raises the temperature of a planetary surface.
Regions of the surface of Ganymede consisting
of parallel grooves; believed to have formed by repeated fracture and
refreezing of the icy crust.
The lowest permitted orbit of an electron
in an atom.
A region of ionized hydrogen around a hot
A plot of the intrinsic
brightness versus the surface temperature of the stars. It separates the
effects of temperature and surface area versus spectral type, but also
luminosity versus surface temperature or color.
The time required for half of the atoms in
a radioactive sample to decay.
The spherical region of a spiral galaxy containing
a thin scattering of stars, star clusters, and small amounts of gas.
A radio galaxy with a contour consisting
of a head and a tail; believed caused by the motion of an active galaxy
through the intergalactic medium.
Thermal energy present in a body as agitation
(motion) among its particles (atoms or molecules).
In planetology, the heat released by the
infall of matter during the formation of a planetary body.
The Sun is at the center of the universe
and everything revolves around that. Was first proposed by Copernicus.
The study of the interior of the sun by the
analysis of its modes of vibration.
The explosive ignition of helium burning
that takes place in some giant stars.
Small nebula that vary irregularly in brightness;
believed associated with star formation.
The formation of a planet by the accumulation
of planetisimals of different composition - e.g. first iron particles,
A star with a large space velocity. Such
stars are halo stars passing through the disk of the galaxy at steep angles.
The assumption that, on the large-scale,
matter is uniformly spread throughout the universe.
The formation of a planet by the accumulation
of planetisimals of the same composition.
In the H-R diagram of a globular cluster,
the sequence of stars extending from the red giants toward the blue side
of the diagram; includes RR Lyrae stars.
A chart showing the location of heavenly
bodies among the zodiacal signs and with respect to the horizon at the
In radio astronomy, a bright spot in a radio
The linear relation between the distance
to a galaxy and its radial velocity.
A measure of the rate of expansion of the
universe; the average value of velocity of recession divided by distance.
The balance between weight of the material
pressing downward on a layer in a star and the pressure in that layer.
A fine network of filaments covering the
sky detected in the far infrared by the IRAS satellite; believed associated
with dust in the interstellar medium.
A sudden brightening of an object at infrared
Electromagnetic Radiation with wavelengths
intermediate between visible light and radio waves
The region of the H-R diagram in which stars
are unstable to pulsation. A star passing through this strip becomes a
The relatively smooth terrain on Mercury.
Time when glaciers melt back (cycles are
roughly 40,000 years)
Dark lines in some stellar spectra that are
formed by the interstellar gas.
The gas and dust distributed between the
Force of gravity decreases as the square
of the distance increases
A tube of magnetic lines and electric currents
connecting Io and Jupiter.
An atom that has lost or gained one or more
The process in which atoms lose or gain electrons.
A galaxy with a chaotic appearance, large
clouds of gas and dust, and both population I and population II stars,
but without spiral arms.
Atoms that have the same number of protons
but a different number of neutrons.
The assumption that in its general properties
the universe looks the same in every direction
A unit of energy roughly equivalent to the
energy given up when an apple falls on the floor. Equivalent to the force
of 1 Newton acting over a distance of 1 meter; 1 joule per second = 1
watt of power.
Jupiterlike planets with large diameters
and low densities.
The Julian Day is the number of days since
the year -4712. The Julian Day begins at 12:00 Noon Greenwich mean time.
Strangely disturbed regions of the moon opposite
the locations of the Imbrium basin and Mare Oriental
The temperature, in Celsius (Centigrade)
degrees, measured above absolute zero.
Orbital motion in accord with Kepler's laws
of planetary motion.
A solution to the equations of general relativity
that describes the properties of a rotating black hole.
A unit of distance equal to 1000 pc or 3260
A set of laws that describes the Absorption
and emission of light by matter.
Points of stability in the orbital plane
of a binary system, planet, or moon. One is located 60 degrees ahead and
one 60 degrees behind the orbiting bodies. Another is located between
the orbiting bodies.
The theory that the moon formed from debris
ejected during a collision between the earth and a large planetisimal.
A graph of brightness versus time commonly
used in analyzing variable stars and eclipsing binaries.
Light Gathering Power
The ability of a telescope to collect light.
Proportional to the are of the telescope objective lens or mirror
Is the distance that light travels in one
year. Abbreviation is ly
A theory that a neutron star produces pulses
of radiation by sweeping radio beams around the sky as it rotates.
The edge of the apparent disk of a body,
as in the "limb of the moon".
The decrease in the brightness of the sun
or other body from its center to its limb.
Line of Nodes
The nodes of the moons orbit are the points
where it passes through the plane of the earth's orbit. An eclipse season
occurs whenever the line connecting these nodes (line of nodes) points
toward the sun.
A graph of light intensity verses wavelength
showing the shape of an absorption line
Liquid Metal Hydrogen
A form of hydrogen under high pressure that
is a good electrical conductor.
A curved cliff such as those found on Mercury.
The theory that quasars are not at great
distances but relatively nearby.
Long Period Variable
A variable star with a period ranging from
100 days to over 400 days.
Look Back Time
The amount by which we look into the past
when we look at a distant galaxy; a time equal to the distance to the
galaxy in light-years.
The total amount of energy a star radiates
in one second.
A category of stars of similar luminosity;
determined by the widths of lines in their spectra.
Lyman, Balmer and Paschen Series
Spectral lines in the UV spectrum of hydrogen
produced by transitions whose lowest orbit of electrons is at ground state
(Lyman). Spectral lines in the visible and near UV of hydrogen produced
by transitions whose lowest orbit is second (Balmer). Spectral lines in
the infrared spectrum of hydrogen produced by transitions whose lowest
orbit is the third. (Paschen)
Small irregular galaxies that are companions
to the Milky Way; visible in the southern sky.
The volume of space around a planet within
which the motion of charged particles is dominated by the planetary magnetic
field rather than the solar wind.
The ability of a telescope to make an image
Method developed by Hipparchus who divided
the stars into 6 classes. The brightest stars are first class and those
slightly fainter are second class. The sixth class is the faintest stars
that he cold see with the unaided eye. The magnitude scale is logarithmic
like the eye.
The region of the H-R diagram running from
upper left to lower right, which includes roughly 90 percent of all stars.
The layer of dense rock and metal oxides
that lies between the molten core and the surface of the earth; also,
similar layers in other planets.
One of the lunar lowlands filled by successive
flows of dark lava.
A measure of the amount of matter in an object
A measure of the ratio of the masses in a
single-line spectroscopic binary. Also includes the inclination, which
is unknown for some systems.
Maunder Butterfly Diagram
A graph showing the latitude of sunspots
versus time, first plotted by W.W. Maunder in 1904.
A period of less numerous sunspots and other
solar activity from 1645-1715.
A unit of distance equal to 1 million pc.
IN astronomical usage, all atoms heavier
A small bit of matter heated by friction
to incandescent vapor as it falls into the atmosphere
A meteor that has survived its passage through
the atmosphere and strikes the ground.
A meteor in space before it enters the earth's
Chasms that split the midocean rises where
the crustal plates move apart.
One of the undersea mountain ranges that
push up from the seafloor in the center of the oceans.
Minute of Arc
A measurement of the sky which includes degrees,
minutes and seconds.. There are 60 minutes of arc in one degree.
Unobserved mass in clusters of galaxies believed
to provide sufficient gravity to bind the cluster together.
An intellectual concept of how nature works
Two or more atoms bonded together.
The measurement of the amount of motion.
the product of mass and velocity
Morning and Evening Stars
A planet visible in the Morning shortly before
sunrise is a morning star, a planet visible just before sunset is the
(nm) 1 x 10-9 meters
Objects move toward their proper place. earth
and water downward, fire and air upward
A cloud of gas and dust in space.
A neutral massless atomic particle that travels
at the speed of light.
An atomic particles with no charge and about
the same mass as a proton.
A small highly dense star composed almost
entirely of tightly packed neutrons; radius about 10 km.
A focal arrangement of a reflecting telescope
in which a diagonal mirror reflects light out the side of the telescope
for easier access
The point twice a month where the moon crosses
the ecliptic. Once a month the moon crosses heading north and two week
later crosses again heading south.
North and South Celestial Poles
The north ands south pivots points around
which the sky appears to rotate.
From Latin meaning "new"; a sudden
brightening of a star, making it appear as a new star in the sky; believed
associated with eruptions on white dwarfs in binary systems.
The spherical cloud of stars that lies at
the center of spiral galaxies.
The production of elements heavier than helium
by the fusion of atomic nuclei in stars and during supernova explosions.
The central core of an atom, containing protons
and neutrons; carries a net positive charge.
In a refracting telescope, the long focal
length lens that forms an image of the object viewed; the lens closest
to the object
In a reflecting telescope the principle mirror
(reflecting surface) that forms an image of the object viewed
A sphere flattened such that its polar diameter
is smaller than its equatorial diameter.
The flattening of a spherical body; usually
caused by rotation
The passage of a larger body in front of
a smaller body.
The conflict between observation and theory
as to why the night sky should or should not be dark.
The resistance of a gas to the passage of
Open (Escape) Orbit
An orbit which leads away from the central
body, never to return
Open Star Cluster
A cluster of 10 to 10,000 stars with an open,
transparent appearance. The stars are not tightly grouped. Usually relatively
young and located in the disk of the galaxy.
A model universe in which the average density
is less than the critical density needed to halt the expansion of the
A binary star in which the stars are only
apparently associated. One star is nearby and one is more distant.
Oscillating Universe Theory
The theory that the universe begins with
a big bang, expands, slows by its own gravity, collapses to create another
The release of gas from a planets interior.
In earth's atmosphere, the layer of oxygen
ions (O3) lying 15 to 30 km high that protects the surface by absorbing
The apparent change in the position of an
object due to a change in the location of the observer. It was because
ancient astronomers did not observe parallax that they though the earth
was the center of the universe and everything in the heavens revolved
A hypothetical distance to a star whose parallax
is one arcsecond; 1pc = 206,265 A.U. = 3.26 ly.
Partial Eclipse (lunar or Solar)
Partial eclipses are caused when the moon
passes through only part of the umbra shadow of the earth. Or when the
earth passes through the only part of the umbra shadow of the moon.
Path of Totality
The path of a total eclipse that is swept
out by the umbra shadow of the moon on the earth.
A Partial blocking of the Sun by the Earth
creates an Penumbra Shadow. The Sunlight is dimmed but not extinguished.
When the moon passes only through the penumbra
shadow of the earth or when the earth passes through only the penumbra
shadow of the moon.
Point of closet approach to the earth
Point in earth's orbit around the sun where
it is closest to the Sun (winter for us)
A graph showing the relation-between period
of pulsation and intrinsic brightness among Cepheid variable stars.
A device used to measure the intensity and
color of light
A quantum of electromagnetic energy Carries
an amount of energy that depends inversely on its wavelength
The bright disk of the sun that is covered
completely by a total Solar eclipse.
Always found near the ecliptic (except Pluto)
An expanding shell of gas ejected by a star
in the latter stages of its evolution.
One of the small bodies that formed from
the solar nebula and eventually grew into protoplanets.
A material with properties of a solid but
capable of flowing under pressure.
The constant destruction and renewal of the
earth's surface by the motions of sections of the crust.
The axis of a telescope around which the
celestial sphere rotates
Poor Galaxy Cluster
An irregularly shaped cluster that contains
fewer than 1000 galaxies, many spiral, and no giant ellipticals.
Stars rich in atoms heavier than helium;
nearly always relatively young stars found in the disk of the galaxy.
Stars poor in atoms heavier than helium;
nearly always relatively old stars found in the halo, globular clusters,
or the nuclear bulge.
The angular direction of one body with respect
to another; measured from north toward the east; typically used in the
study of visual binaries.
A wobbling of the Earth's Axis. It takes
26,000 years for the earth to complete one wobble.
Pressure (P) Waves
In geophysics, mechanical waves of compression
and rarefaction that travel through the earth's interior
In the light curve of an eclipsing binary,
the deeper eclipse.
The point at which an object mirror forms
an image in a reflecting telescope
Earth's first air, composed of gases from
the solar nebula.
Primordial Background Radiation
Radiation from the hot clouds of the big-bang
explosion. Because of its large red shift it appears to come from a body
whose temperature is only 2.7K
A sphere stretched along its polar axis so
its polar diameter is greater than its equatorial diameter.
Eruptions of the solar surface. Visible during
total solar eclipses.
The rate at which a star moves across the
sky. Measured in arc seconds per year.
A positively charged atomic particle contained
in the nucleus of an atom. The nucleus of hydrogen atom.
A series of three nuclear reactions that
build a helium atom by adding together protons. The main energy source
in our sun.
Massive object resulting from the coalescence
of planetisimals in the solar nebula and destined to become a planet.
A collapsing cloud of gas and dust destined
to become a star.
A source of short, precisely times radio
bursts believed to be spinning neutron stars.
The study of behavior of atoms and atomic
Small powerful source of energy believed
to be the active core of very distant galaxies.
Quasi-Periodic Object (QPO)
Certain X-rays sources that "flicker"
rapidly for short intervals.
(Vr) That component of an object's velocity
directed away from or toward the earth.
Radial Velocity Curve
A graph of the velocity of recession or approach
of the stars in a spectroscopic binary.
The force exerted on the surface of a body
by its absorption of light. Small particles floating in the solar system
can be blown outward by the pressure of sunlight.
A galaxy that is strong source of radio signals.
Two or more radio telescopes that combine
their signals to achieve the resolving power of a larger telescope
Ejecta from meteorite impacts forming white
streamers radiating from some lunar craters.
The stage within 1 million years of the big
bang when the gas became transparent to radiation
Stars that erupt as nova every few dozen
Cool, low mass stars on the lower main sequence
A telescope which uses a concave mirror to
focus light into an image
A nebula produced by starlight reflecting
off dust particles in the interstellar medium.
A telescope that forms images by bending
light through an objective lens
A soil made up of crushed rock fragments.
The age of a geological feature referred
to other features. For example, relative ages tell us the lunar maria
and younger than the highlands.
Relativistic Jet Model
An explanation of superluminal expansion
based on a high velocity jet from a quasar directed approximately toward
Relativistic Red Shift
The red shift due to Doppler effect for objects
traveling near the speed of light.
The ability of a telescope to reveal fine
detail. depends on the diameter of the telescope objective
The coincidental agreement between two periodic
phenomena; commonly applied to agreements between orbital periods, which
can make orbits more or less stable.
The planets sometimes speed up in their movements,
slow down, stop and even reverse direction. The motion traces out a retrograde
Rich Galaxy Cluster
A cluster containing over 1000 galaxies,
mostly elliptical, scattered over a volume about 3 Mpc in diameter.
A long, straight, deep valley produced By
the separation of crustal plates.
A galaxy that resembles a ring around a bright
nucleus; believed to be the result of a head-on collision of two galaxies.
The minimum distance between a planet and
a satellite that holds itself together by its own gravity. If a satellites
orbit brings it inside the Roche limit, tidal forces will break the satellite
The most common type of terrain on Venus.
A graph of orbital velocity versus radius
in the disk of a galaxy.
RR Lyrae Variable
Variable stars with periods of 12-24 hours,
common in some globular clusters.
The powerful radio source located at the
core of the Milky Way.
After 18 years and 11 1/3 days the eclipse
pattern repeats The saros cycle does not mean the eclipse will occur in
the same place. Sine the cycle take one third of a day. The earth will
have rotated 8 hours westward from the original location. It takes 3 saros
cycles for the eclipse to repeat in the exact same place or 54 years and
A photographic telescope that take wide angle
Schmidt Cassegrain Telescope
A cassegrain telescope that uses a thin correcting
lens as in a schmidt camera
The radius of the event horizon around a
A method of writing large numbers in a simple
way. For example 380,000 is written 3.8 x106. In scientific notation a
number is always written as a x 10 h Where a >= 1 and a <10.
Caused by the tilt of the earth's Axis 23.5
Second of Arc
See Minute of Arc. 60 seconds of arc make
up one minute.
The gases outgassed from a planet's interior;
rich in carbon dioxide.
In the light curve of an eclipsing binary,
the shallower eclipse
In a reflecting telescope, the mirror that
reflects the image to a point for easy observation
Atmospheric conditions on a given night When
the atmosphere is unsteady, producing blurred images the seeing is considered
A mechanical vibration that travels through
the earth. Usually caused by an earthquake.
An instrument that records seismic waves.
Self-Sustaining Star Formation
The process by which the birth of stars compress
the surrounding gas clouds and triggers the formation of more stars, proposed
to explain spiral arms
Half the long diameter of an ellipse
An otherwise normal spiral galaxy with an
unusually bright, small core that fluctuates in brightness; believed to
indicate the core is erupting.
Shear (S) Waves
Mechanical waves that travel through earth's
interior by the vibration of particles perpendicular to the direction
of the wave travel.
A satellite that, by its gravitational field,
confines particles to a planetary ring.
Wide, low profile volcanic cones produced
by highly liquid lava.
A sudden change in pressure that travels
as an intense sound wave.
The motion and gears on a telescope that
turn westward to keep it pointing at a star
(Sidereal Month) 27.5 Days - Actual Lunar
orbit around the earth. 1 revolution with respect to the stars. Moon drifts
eastward by 13 degrees per day.
A spectroscopic binary in which lines of
one star are visible in the spectrum.
The object of zero radius into which the
matter of a black hole is believed to fall.
A narrow, winding valley on the moon caused
by ancient lava flows along narrow channels.
Apparently young plains on Mercury formed
by lava flows at or soon after the formation of the Caloris Basin
A measure of the energy output of the sun.
The total solar energy striking 1 sq. meter just above the earth's atmosphere
in 1 second.
Solar Nebula Theory
The theory that the planets formed from the
same cloud of gas and dust that formed the sun.
Rapidly moving atoms and ions that escape
from the solar corona and blow outward through the solar system.
Observers can never detect their uniform
motion except relative to other objects. The velocity of light is constant
for all observers
A star's position in the temperature classification
system O,B,A,F,G,K, and M. Based on the appearance of the star's spectrum.
The arrangement of spectral classes (O,B,A,F,G,K,
and M) ranging from hot to cool stars.
Device that separates light by wavelengths
to produce a spectrum
The explosion of a star believed to be caused
by mass transfer to a white dwarf.
Supernova Type II
The explosion of a star believed to be caused
by the collapse of a massive star.
Radiation emitted when high speed electrons
move through a magnetic field.
(Synodic Month) - 29.5 days - One revolution
with respect to the Sun. This is the time frame that determines lunar
phases. Used as the basis for the first Roman Calendar.
T Tauri Stars
Young stars surrounding by gas and dust.
Believed to be contracting toward the main sequence.
A measure of the velocity of random motions
among atoms or molecules in a material.
The dividing line between daylight and darkness
on a planet or moon.
Earthlike planets - small, dense, rocky.
The locking of the rotation of a body to
its revolution around another body.
The heating of a planet or satellite because
of friction caused by tides.
The slowing of time in curved space time,
believed to occur as one approaches the speed of light or crosses the
even horizon of a black hole.
A simple series of steps that produces numbers
approximately matching the sizes of the planetary orbits.
Total Eclipse (lunar or Solar)
When the umbra part of the Earth's Shadow
(lunar eclipse) totally blocks the light being received by the moon, these
can only occur during a Full Moon. A Total Solar Eclipse is the earth
passing through the umbra shadow of the moon and can only occur during
a New moon.
The movement of an electron from one atomic
orbit to another.
The velocity of a star perpendicular to the
line of sight.
A geometrical solid whose three axes are
Triple Alpha Process
The nuclear fusion process that combines
three helium nuclei (alpha particles) to make one carbon nucleus.
True Relative Orbit
The orbit of one star in a visual binary
with respect to the other star after correction for orbital inclination.
Tuning Fork Diagram
A system of classification for elliptical,
spiral and irregular galaxies.
The point on the H-R diagram where a cluster's
stars turn off the main sequence and move toward the red giant region
revealing the approximate age of the cluster.
Electromagnetic Radiation with wavelengths
shorter than visible light but longer than X-rays
Is the Earth shadow that is total. No part
of the Sun can be seen when in the umbra shadow
The density a planet would have if its gravity
did not compress it.
Uniform circular motion
Plato argued that the most perfect form should
be a circle and therefore motions of the heavens should be made of up
combinations of circular motion. The most perfect motion would be uniform
circular motion, so astronomers of ancient times tried to describe the
motions of the heavens in these terms
The assumption that the physical laws observed
on earth apply throughout the universe.
Van Allen Belts
Radiation belts of high-energy particles
trapped in the earth's magnetosphere.
A star whose brightness changes periodically.
A directed rate of motion
Velocity Dispersion Method
A method of finding a galaxy's mass by observing
the range of velocities within the galaxy.
The place where the Sun crosses the celestial
equator heading North.
Very Long Baseline
The use of radio telescopes located thousands
of miles apart to resolve detail in radio sources.
A porous rock formed by solidified lava with
Motion other than natural motion
A binary star system in which two stars are
separately visible in a telescope.
The distance between successive peaks or
troughs of a wave
Wavelength of Maximum
The wavelength at which a perfect radiator
emits the maximum amount of energy; depends only on the object's temperature.
Dying stars that have collapsed to the size
of the earth and are slowly cooling off; at the lower left of the H-R
The point on the ecliptic where the Sun reaches
it most southern point.
The splitting of spectral lines into multiple
components when the atoms are in a magnetic field.
Point in the Sky that is directly overhead.
The locus in the H-R- diagram where stars
first reach stability as hydrogen burning stars.
The 12 constellations near the ecliptic through
which the Sun passes.
A region around the Milky Way where almost
no galaxies are visible because our view is blocked by dust in our galaxy.
Yellow-white regions that circle Jupiter parallel to its equator; believed to be areas of rising gas.
Table of Contents
copyright © Peoria Astronomical Society 1994-2004.