angular resolution
The angular size of the smallest detail of an astronomical object that can be
distinguished with a telescope.
analog
Device which has an output that is proportional to the input.
arcsecond
One-sixtieth of a minute of arc. 1/3600 of a degree.
asteroid
Large piece of rock orbiting the sun,
usually located in the asteroid belt between Mars and Jupiter.
binary star
Two stars revolving about each other; a double star.
cam
A rotating piece that imparts motion to a
roller moving against its edge.
cathode ray tube
A vacuum tube in which high speed electrons are projected under the propulsion
of a strong electric field onto a fluorescent screen.
charge coupled device (CCD)
A type of solid-state silicon wafer designed to detect light.
comparison star
Star used to calibrate either the brightness or position of the unknown star.
comparator
A machine used for looking for parallax motion, proper motion, asteroids, or
variable stars by quickly alternating between viewing two photographic plates
from two different times.
cosmology
The study of the formation, organization, and evolution of the universe.
dark matter
The undetected matter in the universe which is not luminous. We know of its
existence because of how clusters of stars and galaxies rotate.
declination
The coordinate on the sky exactly analogous
to latitude on Earth, measured north and south from the celestial equator.
digital
A way to describe data as a sequence of
discrete symbols, most often this means as binary data using electronic signals.
Doppler equation
The relationship which describes how the change in frequency of light received
from an object depends on the objects velocity from us.
dynode
An electrode in an electron tybe that functions to produce secondary emission of
electrons.
element
A substance which cannot be decomposed by chemical means into a simpler
substance.
emulsion
A light-sensitive coating on paper or film; consists of fine grains of silver
bromide suspended in a gelatin.
encoder
A sensor or transducer for converting rotary
motion or position to a series of electronic pulses.
filar micrometer
An eyepiece which has threads across the
field of view for more accurate measurement.
focal length
Distance from a lens or concave mirror to where converging light rays meet.
focal plane
Plane at the focal length of a lens or concave mirror on which an object is
focused.
focus
Place at the focal length where light rays from an object are converged by a
lens or concave mirror.
frequency
Number of waves that cross a given point per
unit time, or the number of vibrations which occur per unit time.
galaxy
A large group of stars, gas, and dust held together by mutual gravitational
attraction.
globular cluster
Large spherical group of stars bound together by gravity, mostly found in
outlying regions of a galaxy.
gravity
The tendency for all matter to be attracted to all other matter.
heliometer
An instrument devised originally for measuring the diameter of the sun; now
employed for delicate measurements of the distance and relative direction of two
stars too far apart to be easily measured in the field of view of an ordinary
telescope.
interferometry
A method for increasing resolving power by combining light obtained by two or
more telescopes.
iris
Thin overlapping plates which can be adjusted to change the diameter of a
central opening.
lens
A piece of transparent material which is used in an optical instrument for
forming an image by focusing rays of light.
luminosity
The rate at which light is emitted from an
object.
magnitude
A measure of the amount of light received from an object. Higher magnitudes are
fainter objects, lower magnitudes are brighter objects.
mainframe
A large, fast computer which can handle several tasks at the same time.
mass
The total amount of material in an object.
measuring engine
A machine used to measure the positions and brightnesses of objects on
photographic plates.
meteor
A fragment of material from space which falls into Earth's atmosphere and
vaporizes.
Milky Way Galaxy
The galaxy in which our solar system resides.
microphotometer
A machine used to measure the brightness of an object or a spectral line on a
photographic plate.
oscilloscope
An instrument in which the variations in a fluctuating electrical signal appear
as a visible wave on the fluorescent screen of a cathode ray tube.
parallax
The apparent motion of an object caused by viewing the object from different
locations.
photocathode
A cathode which emits electrons when exposed to light.
photomultiplier tube
An instrument in which electrons released by photoelectric emission are
multiplied in successive stages by dynodes which produce secondary emission in
order to amplify an image to see smaller details.
photographic plate
Photograph of the sky taken on a light-sensitive emulsion atop a piece of glass.
pitch
The number of threads in a screw per inch.
pixel
One square of a grid into which the light-sensitive component of a CCD is
divided.
precession
The slow, conical motion of the Earth's axis of rotation caused by the
gravitational pull of the Moon and Sun on Earth's equator.
prism
Wedge-shaped piece of glass used to disperse light into a spectrum.
proper motion
Change in the location of a star on the sky.
quasar
Object which appears starlike but is very
far away and so it is thought to be a galaxy.
radial velocity
Portion of an object's velocity which is parallel to the line of sight.
radiation
Light.
reseau
A system of lines forming small squares of
standard size photographed by a separate exposure on the same plate with star
images to facilitate measurements.
resolution
The degree to which fine details on an image can be distinguished.
reticle
A wire or cross hair in the focus of an eyepiece.
right ascension
The coordinate on the sky analogous to longitude on Earth, measured around the
celestial equator from a specific place in the sky known as the vernal equinox.
servo
A power-driven mechanism that automatically controls the performance of a
machine.
spectral line
A dark or bright line at a specific wavelength in a spectrum.
spectroscopy
The physics that deals with the theory and interpretation of electromagnetic
radiation.
spectrum
Separation of light into its component wavelengths.
star
A self-luminous sphere of gas.
thread
A projecting helical rib by which parts can
be screwed together.
variable star
A star which has variable luminosity.
velocity
A quantity which describes both the speed and direction of an object.
vernier scale
A short scale made to slide along the divisions of a graduated instrument for
indicating parts of divisions, to obtain very fine adjustments.
Very Large Baseline
Interferometry VLBI A technique to
connect widely separated telescopes to make observations with very high
resolution.
wavelength
The distance between two successive peaks of a wave.
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