What is the Atmospheric Window?

The Universe emanates radiation in all longitudinal directions and waves of the electromagnetic spectrum. This radiation is present in all areas of life and allows the functioning of most of the planet's ecosystems and warms us by transmitting energy. However, there is a property in the atmosphere that allows the passage of certain radiation to the earth's surface and is called Atmospheric Window.

What is the Atmospheric Window?

It is the special power of the earth's atmosphere to be transparent to certain radiations that arrive from outer space and in turn prevents the passage of other radiations to the surface that would make the existence of life on earth impossible. Generally, the radiations allowed to enter the Earth's surface from the Cosmos are radio waves and visible light. (plus a small fraction of infrared radiation and ultraviolet) which correspond to the so-called optical and radio windows.

atmosphere window

Optical and Radio Window

The Earth's atmosphere has a capacity to absorb electromagnetic radiation from the Universe in most of its wavelengths. There are bands for which the atmosphere is almost transparent, and two of these are wide enough to be of astronomical interest and to be the target of continued study.

The best known is the "Optical Window", which allows the passage of electromagnetic waves that are commonly known as the visible spectrum: wavelengths from approximately 300 to 1.000 nanometers (0,3 to 1 picometer). The second is known as "Radio Window" which extends in wavelengths from 1 millimeter to 15 meters, (300 Ghz - 20 Mhz).

In the zone between the optical window and the radio window, the atmospheric absorption is mainly due to water and carbon dioxide, (some partially transparent bands are also evident here). Regarding the longest wavelengths (between 1 mm and 1 cm), they are responsible for the absorption, mainly, oxygen and water vapor.

Atmospheric Windows to the Electromagnetic Spectrum

Electromagnetic Spectrum is called the energy allocation of the set of electromagnetic waves emitted or absorbed by a substance. Spectra can be observed using spectroscopes that, in addition to granting the possibility of observing the spectrum, allow measurements to be made on it, such as the wavelength, frequency and intensity of the radiation.

The Electromagnetic Spectrum expands from shorter wavelength radiation, such as gamma rays and X-rays, through ultraviolet light, visible light and infrared rays, to longer wavelength electromagnetic waves, such as radio waves. It is possible that the limit for the smallest wavelength is the Planck length and that the maximum limit would be the size of the Universe, although science formally asserts the electromagnetic spectrum is infinite and continuous.

Electromagnetic spectrum

Spectrum Range

The spectrum covers the energy of electromagnetic waves that have different wavelengths. Frequencies of 30 Hz and below are often produced by certain stellar nebulae and are relevant to their study. Very high frequencies such as 2.9 * 1027 Hz have been found. High-frequency electromagnetic waves have a short wavelength and high energy, while low-frequency waves have a long wavelength and low energy.

However, whenever electromagnetic waves are in a medium (matter), their wavelength decreases. The wavelengths of electromagnetic radiation, regardless of the medium through which they travel, are generally quoted in terms of the wavelength in vacuum. Electromagnetic radiation is usually classified according to the wavelength: radio waves, microwaves, infrared and visible region, which we observe as light, ultraviolet rays, X-rays and gamma rays.

Radio waves

Radio waves are usually used by antennas of the appropriate size (according to the principle of resonance), with wavelengths ranging from hundreds of meters to about a millimeter. Its use is applicable to data transmission, through modulation. From wireless networks, mobile telephony, television and magnetic resonance imaging, are just some of the most popular uses of the so-called "Radio Waves".

Radio waves

Microwave oven

They are high-frequency waves and therefore have a very short wavelength, hence their name. Their characteristic property is to excite water molecules and they are located between infrared rays and conventional radio waves. It has a wavelength of approximately 1 mm up to 30 cm. Its use is evidenced in microwave ovens to heat foods that contain liquids.

milky way in microwave

infrared waves

Infrared are waves of the electromagnetic spectrum that lie between visible red light and the beginning waves of the radio wave region. In the space of the Electromagnetic Spectrum it is understood that this radiation is what we notice as heat.

Infrared image of Andromeda

visible region

It is electromagnetic radiation with a wavelength of approximately 400 nm and 700 nm. In this range the Sun and stars similar to it generate most of their radiation and their frequency is above the infrared. The light that we observe is actually a tiny portion of the electromagnetic spectrum. Rainbows are a sample of the visible part of the electromagnetic spectrum.

Andromeda in visible light and infrared

Ultraviolet rays

Also known as UV rays, it is radiation with a wavelength shorter than the violet end of the visible spectrum. Due to its energy, ultraviolet radiation can break chemical bonds, making molecules exceptionally reactive or ionizing them, which would be the guarantor of a change in their behavior, for this reason sunburns and even cancer are attributed to UV rays. of skin

M101: A view in ultraviolet

X rays

X-rays come after ultraviolet. Hard X-rays have shorter wavelengths than soft X-rays. Its usefulness is applicable to see through some objects. The emission of X-rays from neutron stars and accretion disks are what allow the study of these electromagnetic waves. X-rays are useful in medicine and industry. Stars and especially some types of nebulae are the main emitters of x-rays.

X-rays

Gamma rays

Gamma Rays come after X-Rays and are the most energetic photons, and the lower limit of their wavelength is unknown. They provide utility to astronomers in studying high-energy objects or regions, and are useful to physicists because of their penetrating ability and their production of radioisotopes. The wave dimension of gamma rays is measured with high accuracy by means of Compton scattering.

Gamma rays

Emission and Absorption Spectra

The Atomic Emission Spectrum of an element is a set of frequencies of the electromagnetic waves emitted by atoms of that element, in a gaseous state, when energy is communicated to it. The emission spectrum of each element is unique and can be used to pinpoint whether that element is part of an unknown compound.

The absorption spectrum shows the fraction of incident electromagnetic radiation that a material absorbs within a range of frequencies. Each chemical element has absorption lines at some wavelengths, a fact that is related to the energy differences of its different atomic orbitals. In fact, the absorption spectrum is used to identify the component elements of some samples, such as liquids and gases; beyond, can be used to determine the structure of organic compounds.

It is important to point out that, in what is known as Atmospheric Windows, there is only very little or no absorption or emission of electromagnetic radiation by the components of the air between the object to be measured and the measuring instruments.


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