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.

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