Cosmic Radio Show - Glossary Terms

Frequency: a measurable property of light; the number of waves that pass through any given point in one second.

Wavelength: the distance between two successive maxima or minima of a wave.

Galaxy: an organized system of many hundreds of millions of stars, often mixed with gas and dust. The universe contains billions of galaxies.

Milky Way Galaxy: our Galaxy, of which the solar system is a member. The Milky Way can be seen as a wispy band of brightness on clear moonless nights.

Radio dish: a telescope specifically designed to detect radio emission, made up of a large parabolic dish which focuses long radio waves.

Neutral: having neither a positive nor a negative electric charge.

Hydrogen: the lightest element in the universe, composed of one proton and one electron.

Atom: the smallest indivisible unit of matter that retains the properties of an element.

Proton: a subatomic particle possessing positive charge.

Electron: a subatomic particle possessing negative charge.

Spin: a measure of the magnitude and direction of angular momentum in an atom.

Universe: the entirety of all matter and energy.

Big Bang: the initial explosive event marking the beginning of the universe, and responsible for the observed expansion of the universe.

3-degree Kelvin radiation: an observable remnant of the Big Bang, measurable in every direction of the sky (also known as the Cosmic Microwave Background).

COBE: Cosmic Background Explorer, a NASA satellite designed to measure the infrared and microwave background radiation from the early universe, with great accuracy. COBE was launched November 18, 1989.

Doppler Shifting - Glossary Terms

Doppler Shift: measurable displacement of spectral lines due to motion along the observerUs line of sight. The frequency of a known feature appears shifted from where it should be. Also affects the apparent pitch of sound heard from moving objects.

Radar: a tool that bounces radio waves off objects to determine their speed.

Light speed: the speed of light, a natural limit on how fast anything can travel.

Star: a sphere of gas that shines under its own power, by nuclear fusion.

Prism: a cut of glass used to split electromagnetic radiation into its components so that the spectrum may be observed.

Spectral lines: bright and dark features in a spectrum which correspond to the emission and/or absorption (by atoms of a gas) of photons of specific energies.

Light: the portion of the electromagnetic spectrum which corresponds to what the human eye detects, roughly from 4000 (blue) to 7000 (red) Angstroms. (1 Angstrom = 10-10 meters.)

Redshift: an observable shift in a spectral line toward the longer wavelengths due to motion away from the observer.

Blueshift: an observable shift in a spectral line toward the shorter wavelengths due to motion toward the observer.

Spectrum: the array of wavelengths obtained after splitting light (through a prism for example).

Cluster of galaxies: a gravitationally bound collection of galaxies.

Gravity: the attractive force at work between any two objects in the universe, proportional to the product of the two masses and inversely proportional to the square of their separation distance.

Wolf 359 - Glossary Terms

Planet: any large solid body orbiting a star.

6000 K: the temperature, in Kelvin, of the Sun.

Alpha Centauri: the closest star system to the Sun.

Barnard’s Star: the second closest star system to the Sun, showing a very high velocity in the direction of the Solar System.

Red dwarf: a faint, cool star, smaller and dimmer than the Sun.

Wolf 359: third closest star to the Sun.

Orbit: path that one body follows about another, due to the mutual gravitational attraction between the two.

Lunar Love - Glossary Terms

Seven thousand miles around: all right, already: its diameter is 3,500 km and its circumference is 3,500 km times pi (3.1415926....).

Mares: the dark, smooth(er) plains of the Moon, known as 'seas' since the seventeenth century, but in fact containing no water.

Uplands: heavily-cratered, and rougher and brighter in appearance, the uplands are the more mountainous areas that cover most of the Moon's surface.

Basins: the remnants of the largest craters, often showing concentric structures. The two major basins on the Moon are Orientale and Imbrium.

Crater: circular depression excavated by the impact of a meteor or asteroid, often surrounded by a ring of ejected debris.

Center of Attraction: two bodies in space, like the Earth and the Moon, don't in fact "orbit each other". Each orbits a central point defined by the ratio of thie masses. This unmarked mathematical center is known as the Center of Attraction.

Phase: one of the successive stages of illumination of the Moon. The eight phases are, in order: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent.

Wane: the Moon 'waxes' in the first half of its cycle, when the illuminated surface visible from Earth is increasing, and 'wanes' in the second half, when the illuminated surface we see is decreasing.

Twenty-nine days (point five three): the Moon's orbital period around the Earth is 27.32 days - one lunar month. The Moon is locked in phase with the Earth ("synchronous rotation"), so its period of rotation around its own axis is also 27.32 days and it keeps the same face turned towards the Earth. However, the time between successive new Moons is a little different - 29.53 days, due to the distance moved by the Earth around the Sun during this time.

Sea of Tranquillity: Mare Tranquillitatis, where the Apollo 11 astronauts landed. It is the dark 'sea' at about the "two-thirty" position on the Moon's surface, about half way between the center and the edge.

HST Bop - Glossary Terms

HST: The Hubble Space Telescope, a NASA observatory launched into a low Earth orbit by the space shuttle Discovery on 25 April 1990. It has a 2.4m mirror assembly, and high resolution cameras and instruments that observe in the infrared, visible and ultraviolet regions of the electromagnetic spectrum.

Black hole: the end-point of a very massive star’s life. Gravity acts to compress a large mass into a volume that gets smaller and smaller, eventually leaving an infinitely dense point in space or "singularity".

Cepheid: a certain type of variable star whose period is related to its absolute brightness. Observing these stars in other galaxies allows us to determine the distances of those galaxies.

Quasar: an extremely energetic object located at the very edge of the observable universe, implying they existed in the early universe.

Giant: a star whose outer atmosphere has expanded to fill a large volume.

Pulsar: a rapidly rotating, magnetized neutron star that gives off radiation in a beam, like a lighthouse.

Fornax: a cluster of galaxies.

Virgo Cluster: a large, irregular cluster of galaxies neighboring the Local Group, of which the Milky Way is a member.

Supernova: the catastrophic explosion of a star, during which the star becomes millions of times brighter.

Comet: a small body of ice and dust, in orbit about the sun, which can develop a tail of vaporized ices, and a coma of dust and gas.

Hale-Bopp: The Great Comet of 1997, one of the largest and most active comets ever observed, visible to most people in the Northern Hemisphere.

Ion tail: a tail of ionized gases in a comet.

Dust tail: a tail composed of liberated dust in a comet.

COSTAR: Corrective optics package placed on HST during the first servicing mission, to correct for the aberration of the 2.4m primary mirror.

Hubble Constant: the constant of proportionality between distance and velocities of remote galaxies. Its precise value defines the age of the universe.

Electromagnetic spectrum: the entire range of electromagnetic waves, from radio to gamma rays.

Sun Song - Glossary Terms

Solar system: our sun, and the nine planets, their satellites, asteroids, comets and other minor bodies that orbit the Sun.

Mass: a measure of the quantity of matter in a body.

Hans Bethe: a theoretical physicist who postulated nuclear fusion of Hydrogen to Helium as a power source for the Sun.

Nuclear fusion: a thermonuclear reaction in which nuclei fuse together to form a more massive nucleus. Since the resulting nucleus is less massive that the sum of the initial nuclei, energy is released.

Photosphere: the bright, thin layer of the Sun’s atmosphere from which we receive the most visible radiation.

Galileo: a scientist in the early 1600’s who first pointed a telescope skyward. He discovered sunspots, craters on the moon, and the four largest satellites of Jupiter.

Chromosphere: the transition region between the Sun’s relatively cool photosphere, and the hot corona.

Corona: the outermost region of the solar atmosphere, consisting of ionized gas at temperatures of several million degrees Kelvin.

High Energy Groove - Glossary Terms

X-ray: the region of the electromagnetic spectrum beyond ultraviolet, where photons possess greater energy.

Gamma ray: region of the electromagnetic spectrum beyond X-ray, where photons possess the greatest energies.

Density: a measure of how much matter is contained in a volume. The density of an object is defined as its mass divided by its volume. A neutron star, in which a solar mass is confined to a sphere whose radius is roughly the size of Manhattan, is a very high density object.

Infrared: region of the electromagnetic spectrum just past the red side of visible, where lower energy photons radiate.

UV: region of the electromagnetic spectrum just past the blue side of visible, where higher energy photons radiate.

Neutron star: end point of a massive star’s life, in which a great deal of mass is compressed by gravity into a very small volume, such that individual protons and electrons in the original material fuse to form neutrons.

Black body: an idealized perfect radiator that re-emits all radiation incident upon it. The distribution of this radiation depends only on the black body’s temperature.

Gravitational potential well: the deformation of spacetime surrounding a massive object. In Einstein’s Theory of General Relativity, it is the spacetime deformation which gives rise to closed orbits about massive objects.

Cygnus X-1: An X-ray source, this binary star system is one of the best candidates for a black hole in the Milky Way galaxy. Scientists have studied its orbital properties and proved that the central X-ray source must be more than 16 times the mass of the Sun.

Event horizon: the distance from a black hole within which nothing, not even light, can escape.

Axis: the line through a sphere about which the solid body rotates. On Earth, the rotation axis passes through the North and South geographic poles.

Active galaxy: a galaxy whose energy output is greater than a normal galaxy, thought to be caused by the presence of a supermassive black hole at the core.

Swift Song - Glossary Terms

Detector: instrument for detecting something - radiation, for example, in a particular portion of the electromagnetic spectrum.

Sensitivity: what's the faintest object (or emission) you can see with your detector? Often, important discoveries can be made just by observing with a more sensitive detector and being able to make more accurate measurements of stars or galaxies that are fainter or further away.

Black hole: the end-point of a very massive star's life. Gravity acts to compress a large mass into a volume that gets smaller and smaller, eventually leaving an infinitely dense point in space or"singularity".

Neutron star: end-point of a massive star's life, in which a great deal of mass is compressed by gravity into a very small volume, such that individual protons and electrons in the original material fuse to form neutrons.

Panchromatic: when used about a lens or a photographic film, sensitive to all the wavelengths of the visible spectrum. Astronomers now use it as a flashy term for sensitivity to many (or all) wavelengths of the electromagnetic spectrum

Afterglow: the glow that remains after the bright main event is over. Brief bursts observed in gamma-rays often leave remnant longer-lasting bright glows at X-ray and optical energies. "Afterglow" is also, interestingly, the term used to describe the party thrown by groups like The Chromatics after an a cappella concert, in which everyone sings and has fun till late into the night.

Gamma-ray burst: extremely powerful explosion that shines as bright as a billion trillion Suns. Perhaps caused by the merger of two neutron stars, or the collapse of an extremely massive star.

Redshift: an observable shift in a spectral line towards the longer wavelengths due to motion away from the observer.

Swift: the NASA satellite launched in 2003 that will help solve the mystery of gamma-ray bursts.