Microwaves have the longest wavelength

Closer examination of the individual wavelength ranges

- Classification of the electromagnetic spectrum -

The so-called electromagnetic spectrum summarizes the different types of electromagnetic waves. This means that it is divided into different wavelength (or frequency) ranges.

Radio waves are the longest waves. Their wavelength can be between less than a millimeter and more than a kilometer.

Furthermore, the radio waves in
- long waves (LW)
- medium waves (MW)
- shortwave (KW)
- Ultra short waves (VHF)
- Decimeter waves
- centimeter waves
- millimeter waves
- Sub-millimeter waves divided.

We usually encounter radio waves in our everyday lives in radio and television technology. However, they are not only emitted by "artificial" earthly transmitters, but also quite naturally, in different wavelengths from gas clouds and stars in the universe, which can then be received and examined with the help of radio telescopes (such as the 100m Effelsberg telescope).
Roughly speaking, devices similar to those used for receiving terrestrial radio and television transmitters are used to pick up radio radiation from space, whereby the path of the incoming radiation goes via antenna and amplifier.

Microwaves form a subgroup of radio waves. The term microwave is used to summarize decimeter, centimeter and millimeter waves. Their wavelength is between 1mm and 1m, which roughly corresponds to a frequency range of 300 MHz to 300 GHz.
We encounter them on earth mainly in radar technology, microwaves, as well as wireless communication systems and sensor systems.

Infrared, also known as thermal radiation or IR for short, has a wavelength of 780 nm to approximately 1 mm.
Infrared radiation is further divided into

  • far infrared (far infrared - FIR 50 µm - 1mm)
  • medium infrared (mid infrared - MID - approx. 2.5 - 50 µm)
  • near infrared (near infrared - NIR - 780 nm - 2.5 µm)

Every "warm" body (and that is every body with a temperature above absolute zero of approx. -273 ° C or 0 K) emits infrared radiation. The amount of energy emitted and the wavelength distribution of the radiation depend on the temperature of the body. The warmer a body is, the more energy it emits in the form of infrared radiation and the shorter the wavelength of the radiation.

A telescope for FIR and the sub-millimeter range that is to be launched in 2008 is Herschel.
The "long-wave" infrared range (approx. 0.15 - 1 mm), also known as the submillimeter range, is still accessible for observations from special locations on the earth's surface (high altitude, extremely dry air) (see Internship project by Inka Hammer). A telescope for this spectral range is APEX, located at an altitude of 5100 m in Chile.

The infrared is followed by the small part of the electromagnetic radiation that is visible to the human eye, the so-called visible light. Its wavelength is between 0.4 and 0.8 µm (micrometers or thousandths of a millimeter).

We perceive the different wavelengths of light as colors.

huewavelengthfrequencyEnergy per photon
violet380-420 nm789-714 THz3.26-2.95 eV
blue420-490 nm714-612 THZ2.95-2.53 eV
green490-575 nm612-522 THz2.53-2.16 eV
yellow575-585 nm522-513 THz2.16-2.12 eV
orange585-650 nm513-462 THz2.12-1.91 eV
red650-780 nm462-400 THz1.91-1.65 eV

That follows the visible light Ultraviolet light (short UV)
Its wavelength is roughly between 1 and 400 nm (nanometers).
One differentiates:

  • weak UV rays: 200nm - 380 nm
  • Strong UV rays: 50 nm - 200 nm
  • and
  • XUV (extreme ultraviolet UV radiation): 1 nm - 50 nm

The satellite, for example, provides beautiful images of galaxies in the UV range GALEX.

The so-called radiation is even shorter than UV radiation X-rays (English: X-ray)
The wavelength of these extremely short-wave, high-energy electromagnetic rays is around 10pm - 1nm. The X-ray spectrum thus extends roughly from the shortest ultraviolet to the range of gamma rays. Due to their ability to penetrate most substances, they are mainly used in medicine for x-rays. They were discovered by Konrad Röntgen in 1895.
X-rays generated on other celestial bodies do not reach the earth's surface because they are shielded by the atmosphere. They are being used by researchers using X-ray satellites like CHANDRA and XMM Newtons examined. The most important "X-ray sources" in our cosmos today are: supernova remnants, (active) galaxies and galaxy clusters, X-ray binary stars with compact objects (see below) and the diffuse X-ray background.

The Gamma radiation occupies the last part of the electromagnetic spectrum.
Their wavelength is below 10 pm.

To illustrate how strong gamma radiation is:
"Gamma radiation is so energetic that it can penetrate meter-thick lead plates."
Source: Astronomie.de

The first gamma rays from space were discovered in 1912 when research was carried out on cosmic rays. Becquerel (1903 Nobel Prize) and Paul Villard, who around 1900 clearly recognized that gamma rays belong to electromagnetic waves, are considered to be the discoverers of gamma radiation.
The largest European gamma-ray observatory is called INTEGRAL. On October 17, 2002, 6.40 a.m. CET, ESA's 5-meter-high and 4-tonne high-tech satellite launched from the Russian-Kazakh Baikonur Cosmodrome at the tip of a four-stage Proton launcher. INTEGRAL is intended to record the high-energy gamma radiation in the depths of space that cannot be observed from Earth. The "wanted list" includes exotic objects such as black holes, collapsing stars or the mysterious gamma flashes, the strongest radiation bursts observed in the universe to date.
Source: ESA Local News