Hubble Constant - This number relates the distances of galaxies to their recession velocity and represents the rate at which the universe is currently expanding. Hyperbolic - A trajectory path shaped like a hyperbola. The angle between the orbital plane of a revolving body and some fundamental plane, usually the plane of the celestial equator. Infrared - Electromagnetic radiation whose wavelength is longer than the longest visible red but shorter than radio waves. Interferometery - The location and examination of sources of electromagnetic radiation through the simultaneous use of two or more separated telescopes.
Interferometers produce overlapping wave patterns from the radiation.
These patterns are studied to determine the brightness and angular structure of the emitting source. Ion - An atom or molecular fragment that has a positive electrical charge due to the loss of one or more electrons. The simplest ion is the hydrogen nucleus, a single proton. Absolute zero, or 0 Kelvin corresponds to -273 degrees Celsius. Leading Side - For a satellite that keeps the same face toward the planet, the hemisphere that faces forward, into the direction of motion.