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Living on the Moon? This may perhaps sound somewhat unrealistic today, but the urbanization of the Moon is one of the future topics in space travel. Limited resources on the Moon, the lack of fossil fuels, and extreme conditions such as very high and very low temperatures and a different day/night rhythm necessitate new ideas for energy supply and for the production of the required components and parts.

To come straight to the point: No, assuming it is not coated. Any body with a temperature above absolute zero (-273.15°C) emits electromagnetic radiation whose wavelength λ is linked to its absolute temperature T in Kelvin (K) through Wien's displacement law (named after its discoverer, Wilhelm Wien (1864 - 1928)). Evolution endowed us with eyes with which we are able to see a tiny section of the electromagnetic spectrum, namely wavelengths of between around 400 nm and 750 nm. Longer wavelength radiation is perceived by us as heat, whilst shorter wavelength radiation tans our skin and damages it if such radiation is enjoyed to excess. For thermal radiation, we must distinguish between the near (NIR, λ = 780 ... 3,000 nm), mid (MIR, λ = 3,000 ... 50,000 nm), and far (FIR, λ = 50,000 ... 1,000,000 nm) infrared.

Glass as a material is fascinating due to a number of outstanding properties. The most important of these is its high transparency across the entire visible spectrum, which enables a color-neutral view of the outside world. But let us also take a look at the less pleasant properties of glass. A pane of glass reflects around 8.3 % of the incident light and therefore works like a weak mirror (especially against a dark background). In everyday life, these reflections may not be particularly disturbing, but with high-quality optical components they are not tolerable.

I have taken the seventieth birthday of the Fraunhofer Gesellschaft in 2019 as an opportunity to take a closer look at the quantum leap. After all, the famous Fraunhofer lines which are direct consequences of quantum leaps. Around 1814 our namesake Joseph von Fraunhofer discovered around 570 mysterious black lines in the emission spectrum of the sun. He catalogued them meticulously, but was unable to explain their origin; this would have indeed been impossible back then, without the modern physics of the 20th century. If, for example, sunlight is broken down into its spectral colors through a high-resolution optical grating, “the corresponding colors are missing at the positions of the Fraunhofer lines”.

Part 3 of the Answerd series “How is vacuum generated“ ends the excursion into the basics of vacuum technology with Professor Bräuer and summarizes amongst others once again the most important pump types with their application area together.

”Wind is air which is in a hurry.” In the Earth's atmosphere, airstreams flow from high-pressure areas to low-pressure areas. We experience them as winds, storms or hurricanes. The Coriolis force forms them into vortices.

It is trivial: To remove gases from a given volume we have to pump. We know this from pumping of liquids. However, there are fundamental differences between pumping of liquids and pumping of gases. Liquids are incompressible, at constant temperature they don’t change their volume even if highest pressures are applied. This principle is used in hydraulic power transmission.

At Leybold-Heraeus, at that time a market leader in vacuum plant construction, I learned the following ambiguous statement: “We’ve got a vacuum in our heads!” The ancient Greeks had already been involved with vacuums in around 500 BC. In order to make use of the vacuum technically, for instance to deposit high-quality thin films, we definitely need matter as well as electrical and magnetic fields, and, depending on the circumstances, radiation too. We use highly rarefied gases to operate low-pressure plasmas, which in turn serve as an energy source during the depositing of coatings. Nowadays, physicists define a vacuum strictly as a space containing neither matter, radiation nor force fields.