Glossary of Terms
- 26Al (26-aluminum)
- A radioactive isotope of aluminum that has a half-life of about a million years. When it decays, it produces gamma-rays. It is
produced inside massive stars before they supernova, and so its detection is an indication of where in our galaxy supernovae have
- absorption line
- Colors missing in a continuous spectrum because of absorption of those photons by some intervening material.
- In gamma-ray bursts, emission seen after a GRB, which can be seen in X-rays, optical, and radio. Afterglow can last for days or even
- The opening in a telescope that admits light.
- An angular unit of measure; 60 arcminutes make up one degree.
- An angular unit of measure; 60 arcseconds makes up an arcminute, or 3600 arcseconds makes up one degree.
- Able to act independently. In the case of Swift, this means that the spacecraft can repoint itself without ground controllers feeding
- In astronomy, a background is the "noise" seen in any detector. A familiar example is the static picked up by a cell phone. The
static is inevitable, but is not part of the original message sent by the caller.
- black hole
- One possible end point of a star's life. It is so dense that not even light can escape it's surface.
- Burst Alert Telescope (BAT)
- The gamma-ray detector aboard Swift. BAT will watch the sky for sudden bursts of gamma-rays.
- Burst And Transient Source Experiment (BATSE)
- One of four experiments aboard the Compton Gamma-Ray Observatory. BATSE observed nearly the entire sky for transient
sources, and could position these sources more accurately than earlier experiments.
- Cadmium-Zinc-Tellurium (CZT)
- A semiconductor used in the detection of gamma-rays.
- Charged Coupled Device (CCD)
- Device which detects incoming photons by storing charge produced by the interaction of the photon and detector material, then
transferring that charge sequentially to an amplifier and detector.
- coded aperture mask
- A method of determining the direction of a gamma-ray in a gamma-ray telescope. Consists of a plate of material constructed
of tiles with a random half-open, half-closed pattern, which causes incoming gamma-rays to cast a shadow-pattern on the detector
which can be used to determine the direction of the gamma-rays.
- cosmological distance
- Distances corresponding to a time when the age of the universe was a small fraction of its current age.
- count rate
- In astronomy, the number of photons registered by a detector each second.
- electromagnetic spectrum
- The range of all wavelengths (energies/frequencies) of electromagnetic radiation.
- emission line
- An energy peak in a continuous spectrum caused by the emission of those photons by the de-excitation of electrons in atoms.
- A measure of energy. It is equivalent to 10-7 Joules, or is about enough energy to light a 60 Watt light bulb for about 2
nanoseconds (2 billionths of a second).
- Outside of the Milky Way Galaxy.
- In astronomy, the angular area that a telescope can 'see'.
- filter (U, B, V)
- In optical astronomy, a filter is used to limit the wavelength of light allowed into a telescope's detector. The U filter centers on 360
nanometers, the B filter on 440 nanometers, and the V filter on 550 nanometers.
- filter wheel
- In optical astronomy, a wheel holding several different filters mounted on a telescope.
- The rate that energy crosses a given surface (real or imaginary).
- gamma ray
- The region of the electromagnetic spectrum defined by radiation energies above 1 million eV (or wavelengths less than 0.001
nanometers); this waveband represents the highest energy band in the electromagnetic spectrum.
- gamma-ray burst (GRB)
- A brief, but brilliant, burst of gamma-rays coming from a random point in the sky about once per day.
- grazing incidence
- In terms of mirrors, this refers to shining light onto the mirror at a very shallow angle - nearly parallel to the surface of the
mirror; this is the only way to focus X-rays with a mirror
- A specialized prism for taking spectra.
- hard X-ray
- X-rays on the harder, or more energetic, end of the spectrum, loosely defined as X-rays with energies above 10 keV
- High Energy Astronomy Observatory (HEAO-1 A4; August 1977 - January 1979)
- HEAO-1, the first of three High Energy Astronomical Observatories. A4 was the Hard X-Ray/Low Energy Gamma Ray Experiment aboard
HEAO-1, which completed an all-sky hard X-ray survey.
- An explosion about 100 times more powerful than a supernova explosion, caused by the collapse of a very massive star (mass greater
than about 40 Suns).
- Imaging Compton Telescope (COMPTEL)
- One of four experiments aboard the Compton Gamma-Ray Observatory. COMPTEL produced an all-sky map of gamma-ray emission
line, 26Al, which showed us the locations of nucleosynthesis and massive stars throughout the Galaxy
- For gamma-ray bursts, a measure of the strength of a burst. It is measured as the number of photons crossing a given surface
(i.e. the detector) per second.
- light year
- A measure of the distance light travels in one year; equal to about 9.5 x 1012 kilometers, or 5.9 x 1012
- light curve
- A graph of an object's changing brightness over time.
- For gamma-ray bursts, the area of the sky from which the burst occurred. The smaller the area a telescope is able to pinpoint a
burst to, the better the localization.
- Milky Way Galaxy
- The galaxy that the Sun and Solar System (and Earth) are in.
- nanometer (nm)
- A unit of distance that is one billionth of a meter (10-9 m).
- In astronomy, a relatively small field-of-view for a telescope.
- neutron star
- One of the possible end-points of a star. A neutron star is very dense, with the mass of about 1.4 Suns contained in a sphere
with a radius of about 10 km.
- Oort cloud
- An spherical envelope of small bodies theorized to surround our Solar System at 0.1 to 1 lightyear, and proposed to be the
source of the longest-period comets.
- optical radiation
- The narrow part of the electromagnetic spectrum that can be picked up by human eyes, specifically the region with wavelengths
ranging from 400 to 700 nanometers or with energies of 2 - 3 eV.
- In astronomy, energy sent out from a source as light (photons).
- radio waves
- The lowest energy portion of the electromagnetic spectrum, with wavelengths longer than a meter or energies of below one
millionth of an eV (below 10-6 eV).
- The shift in energy (or wavelength) of a photon emitted when moving away from an observer; in cosmology, the redshift is a
measure of the distance from the observer of the source emitting the photons.
- In astronomy, to turn a telescope about a fixed point or axis.
- solar system
- The Sun and the objects orbiting it, including the planets, asteroids and comets.
- The amount of energy given off by an object at measured energies (plural, spectra)
- An explosion caused by the death of a massive star. At its peak energy output, a supernova can outshine a galaxy.
- In astronomy, a source that suddenly changes, such as appearing, disappearing or drastically brightening or dimming.
- In astronomy, a pre-defined set of conditions met by a detector, initiating a set of observations or data-collection. The trigger
conditions vary by detector and mission.
- ultraviolet light
- The portion of the electromagnetic spectrum from about 5 - 400 nanometers; this is the form of light responsible for a suntan.
- Ultraviolet/Optical Telescope (UVOT)
- The ultraviolet and optical telescope aboard Swift, designed to observe GRBs and their afterglow.
- A region of the electromagnetic spectrum defined by a range of energies (or, equivalently, frequencies or wavelengths).
- The distance between two successive peaks or troughs of a wave; for light, this uniquely specifies the energy and frequency of
- The region of the electromagnetic spectrum from about 0.001 - 1 nanometers (1 keV - 1 MeV).
- X-Ray Telescope (XRT)
- The X-ray telescope aboard Swift, designed to observe GRBs and their afterglow.