It is an airglow emission that there are many vibrations bands, the main band is centered in 864 nm and its total intensity is around 3000 to 6000 R.

The factor that relates the vertical critical frequency to the MUF for an HF circuit. It is denoted by M(D)layer, where D is the path length of the circuit and layer indicates which ionospheric region is being considered, i.e., E, F1 or F2. This factor increases with increasing path length so longer circuits will normally use higher frequencies.

It is the main airglow emission, its spectrum is comprehended between 520 nm and 4 mm. Its intensity is larger than 1000 R.

Nightglow emission with a wavelength of 557.7 nm and intensity of about 100-200 Rayleighs, resulting from the decay of atomic oxygen in the excited state 1S.

Nightglow emission with a wavelength of 630 nm and intensity of about 50-300 Rayleighs, resulting from the decay of atomic oxygen in the excited state 3P.

Nightglow emission with a wavelength of 777,4 nm and intensity of about 20 Rayleighs. It is the result of the mechanisms of radiative recombination and ion-ion recombination.

Denomination of the electromagnetic radiation in visible spectrum. Extents from 400nm to 700nm.

This is a statistical prediction of the highest frequency for HF sky wave propagation. If the prediction is correct, this frequency should be refracted by the ionosphere 90% of the time. See Maximum Usable Frequency and Upper Decile MUF.

The gravitationally curved (usually elliptical) path of one object around a point or another body.

In this calendar the format of the day numbers is written continuously inside each year. So the ordinal day 001 corresponds to January 1st and 365 to December 31 (for a non leap year).

The radio wave that follows the laws of refraction when propagating in a plasma containing a magnetic field. For the ordinary wave, the electric vector rotates in the opposite direction to that of an electron gyrating in the field when propagation is along the direction of the magnetic field. For propagation perpendicular to the magnetic field, the electric vector oscillates parallel to the magnetic field.

A wavelike airflow produced over and in the lee of a mountain barrier.

A form of oxygen, O3. A powerful oxidizing agent that is considered a pollutant in the lower troposphere but an essential chemical in the stratosphere where it protects the Earth from high-energy ultraviolet radiation from the sun.

An atmospheric layer that contains a high proportion of oxygen that exists as ozone. It acts as a filtering mechanism against incoming ultraviolet radiation. It is located between the troposphere and the stratosphere, around 15 to 20 kilometers above the Earth's surface.