The time period when the sun is no more than 6 degrees below the horizon at either sunrise or sunset. The horizon should be clearly defined and the brightest stars should be visible under good atmospheric conditions (i.e. no moonlight, or other lights). One still should be able to carry on ordinary outdoor activities.
The time period when the sun is between 6 and 12 degrees below the horizon at either sunrise or sunset. The horizon is well defined and the outline of objects might be visible without artificial light. Ordinary outdoor activities are not possible at this time without extra illumination.
The time period when the sun is between 12 and 18 degrees below the horizon at either sunrise or sunset. The sun does not contribute to the illumination of the sky before this time in the morning, or after this time in the evening. In the beginning of morning astronomical twilight and at the end of astronomical twilight in the evening, sky illumination is very faint, and might be undetectable.
The time of Civil Sunset minus the time of Civil Sunrise.
The time of Actual Sunset minus the time of Actual Sunrise. The change in length of daylight between today and tomorrow is also listed when available.
Solar irradiance is the power per unit area (watt per square metre, W/m2), received from the Sun in the form of electromagnetic radiation.
Temperature is a measure of the warmth or coldness of an object or substance with reference to a
standard value. It can be measured in Kelvin (K), Fahrenheit (F), or Celsius (C).
Air in motion relative to the surface of the earth. Wind develops from pressure differences in the
air. An area of high pressure and low pressure oppose each other and set up a pressure gradient force that moves
from high to low pressure. This force creates a wind as air is pushed in the according direction. The stronger
the pressure difference, the stronger the force, and the stronger the resultant wind. Wind is described as the
prevailing direction of which the wind is blowing as a speed in units of miles per hour or knots.
The force exerted by the weight of the atmosphere and gravity. Different units: atmospheres (atm),
millibars (mb), pascals (Pa), inches of mercury (in), pounds per square inch (PSI), etc. Meteorologists most often use mb.
The rain measured in a specified period of time (e.g. daily, monthly, yearly).
That part of the electromagnetic spectrum between 5 - 400nm.
