Technical Terms relating to the Princeton OSETI Project

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The amount of data that can be transmitted in a given time. Expressed in bits per second for digital transmissions and in hertz for analog transmissions. The bandwidth for a signal being transmitted cannot exceed the frequency of its carrier wave. Since visible light waves have a much higher frequency than radio waves (other than this the two are the same), data can be sent much faster using visible light waves as a carrier.


A Cerenkov light flash is analogous to a sonic boom for sound, which is caused by an object exceeding the speed of sound. Nothing can exceed the speed of light in a vacuum, but objects can exceed the speed of light in other media. For example, high energy particles can exceed the speed of light in air or water. When they do so, the particles emit Cerenkov radiation, which is visible as a flash of blue light. This is a natural phenomenon that occurs in the atmosphere and could potentially cause misreadings in an OSETI detector.


The angular position of a star in the sky with respect to the celestial equator. For example, a star that appears directly above the equator (i.e. - a line drawn from the center of the Earth to the star goes through the equator) would have a declination of 0° A star that appears directly above the North pole would a declination of 90°, and a star that appears directly above the South pole wold have a declination of -90°

electromagnetic spectrum

Electromagnetic radiation is the propagation of an electromagnetic field through space. This process is analogous to the waves that propagate when one tosses a stone into a pond. When a charged object such as an electron vibrates, an electromagnetic wave emanates like the wave that spreads out from where the stone entered the water. All the waves travel at the speed of light. The waves are characterized by their frequency or wavelength. The chart below summarizes the different frequencies of electromagnetic radiation.

The light that we see with our eyes and the radio waves we pick up on our radios are basically the same thing - electromagnetic radiation - only at different frequencies. The only thing that makes visible light special is that our eyes are tuned to see this range of frequencies and to interpret this as color.


The number of cycles that occur in a given time. For a wave, the number of times the wave goes from peak to peak in a second, measured in cycles per second (hertz). A 21cm microwave has a frequency of 1.4 billion hertz. Red light has a frequency of about 430 trillion hertz.


Unit to measure frequency. Equals cycles per second.


Measurement of energy. 1 Joule is about the energy needed to lift 1 pound up 8.7 inches or in metric, 1 kilogram, 10 centimeters.


Acronym for Light Amplification through Stimulated Emission of Radiation. A LASER is a light source that creates an intense, narrow beam of light of a specific frequency, where all the waves are very nearly in phase (coherent) with one another.

light year

Measure of distance, abbr.- ly. Equal to the distance that light travels in a vacuum in one year. When one observes the light from a star 100 ly away, one is observing the star as it was 100 years ago. Also approximately equal to 9.5 trillion kilometers.


Acronym for Microwave Amplification by Stimulated Emission of Radiation. MASERs were the predecessors of LASERs, and operate on the same principle, but with microwaves instead of with visible light.

Metric prefixes

101da-deka- or deca-

These prefixes are used in the metric system to describe variations on a unit of measure that is smaller or larger than the standard unit. For example, a megahertz (MHz) is equal to 106 or 1,000,000 Hertz, and a nanosecond (ns) is equal to 10-9 or .000000001 of a second.


Portion of the electromagnetic spectrum between the wavelengths of radio waves and infrared light.


Position of a wave relative to another fixed wave, measured in degrees. For example, when the top or peak of one wave passes a particular point at the same time as the bottom or trough of another wave of equal frequency, the waves are said to be out of phase by 180°


The primary mirror of a reflecting telescope is the larger of the two mirrors, and is the one the light initially hits. From there it is focused onto the secondary mirror, which then directs the light to the eyepiece.

right ascension

Right ascension is similar to longitude with the exception of the way that it is measured. R.A. uses hours, minutes, and seconds of time to measure the position of a star instead of degrees, minutes, and seconds of angle. This is convenient since it is related to the rotation of the Earth. If two stars are 3 hours apart in R.A. and the telescope is pointing at the first star, then three hours later the telescope will be pointing at the second star.


The distance between two corresponding parts of a wave, such as their peaks. Light waves, for example, have wavelengths between about 400 nm and 700 nm.

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