Glossary

A logarithmic measure of the power output or luminosity of a star or other object. By definition, the absolute magnitude of a star is equal to the apparent magnitude the star would have if it were located 10 parsecs from Earth.

The rate of change of velocity. This may be a change in speed, or it may be a change in direction. For example, pushing on the gas accelerates you car forward, hitting the breaks accelerates it backward, and turning the steering wheel accelerates it sideways.

a device which turns the tiny variations in the impinging electric field into tiny electric currents in a wire

The equivalent temperature that a radio telescope measures. It includes both the source and the noise.

The method of combining the signals from multiple radio telescopes to produce high resolution radio maps.

A measure of how bright an object (such as a star) appears as seen from Earth. For historical reasons, smaller numbers signify brighter stars. The faintest stars visible to our most powerful telescopes are about magnitude +30; the faintest stars visible to the human eye are about magnitude +6, and Sirius, the brightest star in the nighttime sky, has apparent magnitude of -1.4. A difference of 1.0 magnitude corresponds to a brightness ratio of 2.512.

Here the telescope beam is the area in the sky being observed by the telescope.

Celestial coordinates, Right Ascension and Declination, precessed to the date January 1, 1950 at the time that the solar longitude is exactly 280º.

The Besselian system is named after the German astronomer Friedrich Bessel (1784–1846), who was the second astronomer to measure the parallax of a star.

A terrestrial source of radio emission, which can interfere with one's observation.

Thermal radiation from an opaque (non-transparent) source at a given temperature. For example, you radiate blackbody radiation peaking in the infrared part of the spectrum, while the sun emits blackbody radiation primarily in the visible.

A measure of the radiant energy arriving at the location of an observer or sensor, per unit time, per unit area. Typically measured in watts per square meter.

The temperature an extended source would have if it were thermal. For a particular radio antenna, the brightness temperature is proportional to the flux density of the source.

The rate of change of the velocity vector due only to its change in direction.

A particle that is electrically charged either positively or negatively. The two most common charged particles are electrons and protons.

A data recorder, where a pen moves on one axis as the paper unrolls. They are also called strip chart recorders. Now they have been replaced by analog to digital converters, except in historical radio telescopes.

A type of scan which move the telescope in a "daisy" pattern,
repeatedly over the object being observed so that both signal and
noise can be effectively distinguished.

Electronic equipment capable of converting incoming currents or voltages into a measure of power

Here drifted means moved with the celestial sphere as it appears to rotate around the earth.

The force per change, usually due to the movement of other charges.

An oscillating electromagnetic field, which travels at the speed of light. Light is an electromagnetic wave.

An astronomical object with an angular size greater than the resolution of the telescope.

The small antennas at the focus of a radio telescope. Also called probes. There are usually two feeds per frequency, one for each polarization of the light. The term is a holdover from early radar work where they fed energy to the system to be beamed out.

The box of electronics that houses the feeds in a radio telescope. The colder this box is kept, the lower the noise.

a part of a radio telescope that collects the signal reflected from the primary or secondary reflector and channels it into a receiver. It often looks like a funnel.

A plot of the signal as a function of time within only one period. All signals with the same phase are averaged together. Sometimes these are plotted double for presentation purposes.

Mixing or combining signals of two frequencies to produce one at another.

The local meridian is an imaginary line running across the sky from the northern horizon to the southern horizon passing through the North celestial pole (South in the southern hemisphere) and the Zenith. It is a line of RA. What objects are on the local meridian depends on the time of day and on your location. When an object transits (crosses) the local meridian, it is at its highest point in the sky from the observing location.

A numerical scale in which differences correspond to ratios of the measured quantity. Examples include the Richter scale for earthquakes (in which a difference of one magnitude is a ratio of ten in the energy released by an earthquake; a magnitude 7.0 earthquake is ten times more violent than a 6.0 earthquake); apparent magnitude and absolute magnitude, in which a magnitude difference of 1.0 corresponds to a ratio of 2.512 in brightness and luminosity, respectively.

The smallest a quantity could be.

The power output of a light source, such as a star. The actual energy released, per unit of time, regardless of how distant the star is. Typically measured in watts or using absolute magnitude.

Where magnetic field lines enter, or exit, an object.

Polarization tells us how an electromagnetic wave is oriented relative to the antennas

The point at which the main mirror (reflector) brings incident light to its greatest concentration

a computer or electronics that analyze pulsar data on the fly at the radio telescope.

Using radio antennas to observe natural electromagnetic emission with wavelengths longer than about a millimeter.

An electronic device that amplifies, detects, and gives a measure of the intensity of radio signals.

Pertaining to the principle of relativity, which was thought up by Galileo in the 1600s.

Alternatively, it can refer to Einstein's theory of relativity, thought up in the early 20th Century.

Sometimes it simply means that a particle is traveling at almost the speed of light, or more precisely that a particle's kinetic energy is greater than its mass energy.

In a time data series such as a digitized radio signal, this is another time data series where each datum represents the median of it and its surrounding data. This is often called "median smoothing" because it produces a smooth curve and ignores the exceptions, such as pulses.

Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. (Wikipedia)

Synchrotron radiation is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity. (Wikipedia)

Temperature is a measure of the average kinetic energy of the particles (atoms and molecules) making up a substance. Higher temperature means these microscopic particles are moving faster.

The light radiated from an object because of its temperature. This is usually, but not always, black body radiation.

A telescope that points along its local meridian. These are only steerable in declination. Historically there have been both optical and radio transit telescopes; they are more likely to be found in the radio world where observations can be made both day and night.

The largest a quantity could be.  Example:  "The speed of light is the upper limit on velocity."

A random radio signal that is largely independent of frequency.