Hello friends, continuing with the previous posts 1 - 2 -3 today I will talk about the last part of basic concepts in astronomy.
Absolute temperature: Absolute temperature, also called thermodynamic temperature, is the temperature of an object on a scale where 0 is taken as absolute zero. Absolute temperature scales are Kelvin (degree units Celsius) and Rankine (degree units Fahrenheit).
Ideal gas: An ideal gas is a theoretical gas composed of many randomly moving point particles whose only interactions are perfectly elastic collisions. The ideal gas concept is useful because it is the ideal gas law, a simplified equation of state, and is amenable to analysis under statistical mechanics.
Image source [1]: Carnot engine diagram (modern) - where an amount of heat QH flows from a high temperature THfurnace through the fluid of the "working body" (working substance) and the remaining heat QC flows into the cold sink TC, thus forcing the working substance to do mechanical work W on the surroundings, via cycles of contractions and expansions.
Density: The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:
Image source [2]: A graduated cylindercontaining various coloured liquids with different densities.
The albedo of a planet: The term albedo, denoted by A, depends on the ability of a body to reflect light. The planets of our Solar System do not have their own light, but they reflect and absorb it. The brightness of a planet depends on its distance from the Sun and the albedo of its surface. If the albedo of a body is A, the fraction of radiation absorbed by the body is (1 - A). If the body is at a distance r from the Sun, the flow of energy or luminosity absorbed is:
where: