Zeeman Effect
Is the split of an spectral line into several components in the presence of a magnetic field. In most atoms, there exists several electronic configurations that have the same energy, so that transitions between different pairs of configurations correspond to a single line. Named after the Dutch physicist Pieter Zeeman.
Zener Diode
This device is especially designed so as to have a greatly reduced breakdown voltage, the so-called Zener voltage. A reverse-biased Zener diode will exhibit a controlled breakdown and let the current flow to keep the voltage across the Zener diode at the Zener voltage. For example, a 6.2 volt Zener diode will exhibit a voltage drop of 6.2 volt if reverse biased. However, the current is not unlimited, so the Zener diode is typically used to generate a reference voltage for an amplifier stage.
Zenith
Is the point in the sky where you are looking when you look ‘straight up’ from the ground. More precisely, it is the point on the sky with an altitude of +90 Degrees; it is the pole of the horizontal coordinate system. Geometrically, it is the point on the celestial sphere intersected by a line drawn from the center of the Earth through your location on the Earth’s surface.
Zero Point Energy
Is the energy in a system when the temperature is reduced to absolute zero (0 Kelvin -2730 Celsius).
ZETA (Zero Energy Thermonuclear Apparatus)
Was one of the first large-scale fusion devices built at Harwell to try and produce conditions under which thermal fusion reactions might take place. The first successful experiments were carried out in August 1957.
Zodical Light
Is composed of fine particles of dust in orbit around the sun and is visible because of scattered sunlight from the particles. The glow is brightest toward the sun from particles with diameters between a couple of micrometers and a few millimeters. From the mid-northern latitudes, the Zodiacal light is most easily visible from a dark location under clear and transparent skies just after evening twilight in the west in February and March, and in the morning eastern sky, just before the start of twilight in October. It is best seen at these times because the plane of dust that comprises it lies in the same plane as the ecliptic, and the ecliptic is at it’s steepest angle to the horizon at these times of the year.