The indivisible unit in which waves
may be emitted or absorbed.
theory that describes the
interactions of quarks and gluons.
The ratio of the number of photons incident on a detector to the number actually detected.
The branch of physics that deals with the structure of atoms and their interactions with one another and with
General term for ideas based on
microscopic world that human eyes can't see or feel with our hands. In this
world, there is phenomenon, such as matter that is wave as well as being
particles that you can't explain with the rules in the world that you can see.
This theory was made to explain these circumstances. Having the quantum
hypothesis (Max Planck) in late 19th century as a beginning, many leading
physicists of the time have continued studying.
Famous examples are Heisenberg uncertainty
principle, and Shroedinger's
that feels the strong
force; protons and neutrons are composed of three quarks
A quasi-stellar radio source. These
peculiar objects emit radio waves with a large red shift. The red shift represents the fraction of the percentage in which the
wavelengths are switched.
Quasars are very far away, and very bright, and many astronomers agree that
giant black holes are present within these objects.
Sometimes also called quasi-stellar object (QSO); A stellar-appearing object of
very large redshift that is a strong source of
radio waves; presumed to be
extragalactic and highly luminous.
The technique of bouncing radio waves off an object to
measure its distance or map its surface.
The movement of a
toward or away from an observer.
Radial Velocity Curve
A plot of the variation of radial velocity with time for a binary or
The supplementary SI
unit of angular measure, defined as the central angle of a circle whose
subtended arc is equal to the radius of the circle. One radian is approximately
Radiant (of meteor shower)
The point in the sky from which the meteors belonging to a shower seem to radiate.
Electromagnetic wave which is
emitted by a matter in order to emit light/heat. Example is Sun's rays.
Regions of charged particles in a
The transfer of momentum carried by electromagnetic radiation to a body that the radiation impinges upon.
Electromagnetic radiation which has the lowest frequency, the longest
wavelength, and is produced by charged particles moving back and forth; the
atmosphere of the Earth is transparent to radio waves with wavelengths from a
few millimeters to about twenty meters.
The technique of determining the ages of rocks or other specimens by the amount of radioactive decay of certain radioactive
elements contained therein; something you do when you are desperate on Saturday night.
The property possessed by some elements (as uranium) of
spontaneously emitting alpha or beta rays and sometimes also
gamma rays by the
disintegration of the nuclei of atoms.
A radio-luminous galaxy. Radio galaxies are a part of a larger group of galaxies called active
galaxies. The "active" refers to the fact that the observed radiation
source is non-thermal: Glowing matter does not radiate this "active"
luminous component. Furthermore, radio galaxies are named so because they are
"louder" at radio wavelengths than at visible light
indicates tremendous activity within radio galaxies...something must be driving
the non-thermal emission. Radio telescopes show lobes of radio emission
extending millions of light
years, centered at the nucleus of some radio
galaxies, called extended radio galaxies. Centaurus A is a nearby example of an
extended radio galaxy that features two outer lobes 650,000 and 1,350,000 light-years in diameter. Compact radio galaxies emit radio lobes not much larger
that the galactic nucleus.
Instead of gathering
and focusing visual wavelength light, a radio
wavelength light with a huge dish-shaped antenna. An array of radio telescopes
called the Very Large Array lies 80 kilometers west of Soccoro, New Mexico. VLA
radio telescopes are arranged in a "Y" pattern with each arm
supporting nine 25-meter parabolic dishes. These radio telescopes probe the
galaxy and universe where optical telescopes cannot. Astronomers have mapped the
hydrogen content of our galaxy, and discovered enormous activity and structures
in other galaxies invisible to optical telescopes.
Electromagnetic radiation with very long
produced by gas clouds and energetic objects.
A straight line joining the center of an attracting body with that of a body describing an orbit around it; for example, a line joining the Sun and a planet.
Criterion1.22 x lambda/d
A criterion for how finely a set of optics may be able to distinguish the
location of objects which are near each other. It begins with the assumption
that the central ring of one image should fall on the first dark ring of another
image; for an objective lens with diameter d and employing
light with a
wavelength lambda (usually taken to be 560 nm), the resolving power is
approximately given by
Rayleigh-Taylor instabilities occur when a heavy (more dense) fluid is pushed
against a light fluid -- like trying to balance water on top of air by filling a
glass 1/2 full and carefully turning it over. Rayleigh-Taylor instabilities are
important in many astronomical objects, because the two fluids trade places by
sticking "fingers" into each other. These "fingers" can drag
the magnetic field lines along with them, thus both enhancing and aligning the
A state of stellar evolution beyond the main-sequence life of a star. A red
giant core is degenerate
helium, surrounded by a shell of
fusion, that expands the outer atmosphere in response to higher core
temperatures. The hydrogen fusing shell eats through the surrounding atmosphere
and deposits helium onto the shrinking core. The ballooning atmosphere cools and
glows red; hence red giant. The Sun will become a red giant the size of Earth's
orbit in five to six billion
years. Once the helium core reaches 100 million
degrees, it explosively begins fusing helium. The birth of the active helium
core is called the helium
flash. The Sun as a red giant will fuse helium for
about 2 billion years after the helium flash.
The Doppler effect
shifting light wavelengths to the red end of the
spectrum because of the motion
of the source. A red shift indicates a receding source of light, with the
magnitude of the shift corresponding to the velocity of the source. Astronomers
relate red shifts to a calibrated distance in order to stretch their cosmic yard
stick beyond the local realm of galaxies. Planetary astronomers observe small
red shifts and blue shifts in
stars that unseen planets
For a wavefront intersecting a reflecting surface, the angle of incidence is
equal to the angle of reflection, in the same plane defined by the ray of
incidence and the normal.
telescope that forms an image
A change in the
direction of light that depends on incident angle,
wavelength (color), and the
material. Raindrops refract light into rainbows. Each color is a different
wavelength that refracts at a unique angle, forming a band of color in order of
wavelength: red, orange, yellow, green, blue, indigo, and violet. A prism
behaves the same way using glass instead of water. The refraction happens at the
boundary between two different, transparent materials.
The layer of rocky debris and dust made by
meteoritic impact that forms the uppermost surface of planets,
satellites and asteroids.
General Theory of
A theory formulated by Einstein that describes the relations between measurements of physical phenomena by two different observers who are in relative motion at constant
special theory of
relativity) or that describes how a gravitational field can be replaced by a curvature of
space-time (the general theory of relativity).
In astronomy, the ability of a
telescope to differentiate between two objects in
the sky which are separated by a small angular distance. The closer two objects
can be while still allowing the telescope to see them as two distinct objects,
the higher the resolution of the telescope.
(Spectral or Frequency)
Similar to spatial resolution except that it applies to frequency, spectral
resolution is the ability of the telescope to differentiate two
which differ in frequency by a small amount. The closer the two signals are in
frequency while still allowing the telescope to separate them as two distinct
components, the higher the spectral resolution of the telescope.
A measure of a
telescope's ability to distinguish fine
A relationship in which the
of one body is related to that of another by a simple integer fraction, such as
1/2, 2/3, 3/5.
The rotation or orbital motion of an object
in a clockwise direction when viewed from the north pole of the ecliptic; moving
in the opposite sense from the great majority of solar system bodies.
An apparent backward movement of a superior planet in the
sky, as Earth overtakes it on its journey around the Sun.
An elongated valley
formed by the depression of a block of the planet's crust between two faults or
groups of faults of approximately parallel strike.
The position of a
celestial object in the sky east of the vernal equinox along the celestial
equator. Sidereal hours, minutes and seconds divide the celestial equator from 0
to 24 sidereal hours of right ascension. Keep in mind that the celestial equator
is a projection of Earth's equator onto the sky, and Earth's rotation
24 sidereal hours (23.9345 solar mean hours). Thus dividing the celestial
equator into sidereal hours, minutes and seconds instead of 360 degrees makes
some intuitive sense. Set 1 sidereal hour equals 15 degrees to convert between
right ascension and degrees.
The closest a fluid body can
orbit to its
parent planet without being pulled apart by
tidal forces. A solid body may
survive within the Roche limit if the tidal forces do not exceed its structural
strength. The Roche limit is calculated with the equation:
RL = 2.456*R*(p'/p)^(1/3)
Where p' is the density of the planet, p is the density of the
moon, and R is
the radius of the planet.
The volume around a star in a binary system in which, if you were to release a
particle, it would fall back onto the surface of that star. A particle released
above the Roche lobe of either star will, in general, occupy the `circumbinary'
region that surrounds both stars. The point at which the Roche lobes of the two
stars touch is called the inner Lagrangian
or L1 point. If a star in a close binary system evolves to the point at
which it `fills' its Roche lobe, theoretical calculations predict that material
from this star will overflow both onto the companion star (via the L1 point) and
into the environment around the binary system.
Turning of a body about an axis running through it.
The term applied to
surfaces; many scarps are thought to be the surface expression of faults within
the crust of the planetary object.