What kind of radiation do we emit

Most of the radio part of the EM spectrum falls in the range from about 1 cm to 1 km, which is 30 gigahertz GHz to kilohertz kHz in frequencies. The radio is a very broad part of the EM spectrum.

Infrared and optical astronomers generally use wavelength. Infrared astronomers use microns millionths of a meter for wavelengths, so their part of the EM spectrum falls in the range of 1 to microns. Optical astronomers use both angstroms 0.

Using nanometers, violet, blue, green, yellow, orange, and red light have wavelengths between and nanometers. This range is just a tiny part of the entire EM spectrum, so the light our eyes can see is just a little fraction of all the EM radiation around us. The wavelengths of ultraviolet, X-ray, and gamma-ray regions of the EM spectrum are very small.

Instead of using wavelengths, astronomers that study these portions of the EM spectrum usually refer to these photons by their energies, measured in electron volts eV. Ultraviolet radiation falls in the range from a few electron volts to about eV. X-ray photons have energies in the range eV to , eV or keV. Gamma-rays then are all the photons with energies greater than keV. Show me a chart of the wavelength, frequency, and energy regimes of the spectrum.

Why do we put telescopes in orbit? The Earth's atmosphere stops most types of electromagnetic radiation from space from reaching Earth's surface.

Warmer object emits more thermal radiation than cooler one. Handheld infrared ear or forehead thermometers are used to probe body temperatures by detecting the infrared radiation emitted by human bodies.

Infrared cameras are also used for fast screening of travelers with a fever at airports, ports and border crossings. Higher cloud tops are of lower temperature and emit infrared radiation of smaller intensity. Hence we can observe temperature distribution of cloud tops on an infrared satellite picture.

But this is not the case for all stars. Some stars in our galaxy are somewhat cooler and exhibit a reddish hue, while others are much hotter and appear blue.

The constellation Orion contains the red supergiant Betelgeuse and several blue supergiants, the largest being Rigel and Bellatrix. Can you spot them in this photograph of Orion?

Examine once again the graph of the sun's emission curve versus the Earth's emission curve. Pay particular attention to the energy values on the left axis for the sun and right axis for the earth. The first thing to notice is that the energy values are given in powers of 10 that is, 10 6 is equal to 1,, This means that if we compare the peak emissions from the earth and sun we see that the sun at its peak wavelength emits 30, times more energy than the earth at its peak.

In fact, if we add up the total energy emitted by each body by adding the energy contribution at each wavelength , we see that the sun emits over , times more energy per unit area than the earth!

I calculated the numbers above using the third radiation law that you need to know, the Stefan-Boltzmann Law. The Stefan-Boltzmann Law states that the total amount of energy per unit area emitted by an object is proportional to the 4th power of the temperature. We'll more talk more about this relationship when discuss satellite remote sensing. It is also particularly useful when we want to understand how much energy the earth's surface emits in the form of infrared radiation.

In the preceding radiation laws, we have been taking about the ideal amount of radiation than can be emitted by an object. This theoretical limit is called "black body radiation". However, the actual radiation emitted by an object can be much less than the ideal, especially at certain wavelengths.

Kirchhoff's Law describes the linkage between an object's ability to emit at a particular wavelength with its ability to absorb radiation at that same wavelength. In plain language, Kirchhoff's Law states that for an object whose temperature is not changing, an object that absorbs radiation well at a particular wavelength will also emit radiation well at that wavelength. One implication of Kirchhoff's law is as follows: If we want to measure a particular constituent in the atmosphere water vapor for example , we need to choose a wavelength that is emitted well by water vapor otherwise we wouldn't detect it.

However, since water vapor readily emits at our chosen wavelength, it also readily absorbs radiation at this wavelength -- which is going to cause some problems measurement-wise. Well look at the implications of Kirchhoff's Law in a later section. For now, we need to complete our discuss of radiation by looking at the possible things that can happen to a beam of radiation as it passes through a medium.

Beta-emitters are most hazardous when they are inhaled or swallowed. Gamma rays can pass completely through the human body; as they pass through, they can cause damage to tissue and DNA. Radioactive decay occurs in unstable atoms called radionuclides. The energy of the radiation shown on the spectrum below increases from left to right as the frequency rises.

Other agencies regulate the non-ionizing radiation that is emitted by electrical devices such as radio transmitters or cell phones See: Radiation Resources Outside of EPA. Alpha particles come from the decay of the heaviest radioactive elements, such as uranium , radium and polonium. Even though alpha particles are very energetic, they are so heavy that they use up their energy over short distances and are unable to travel very far from the atom.

The health effect from exposure to alpha particles depends greatly on how a person is exposed. Alpha particles lack the energy to penetrate even the outer layer of skin, so exposure to the outside of the body is not a major concern. Inside the body, however, they can be very harmful.

If alpha-emitters are inhaled, swallowed, or get into the body through a cut, the alpha particles can damage sensitive living tissue.

The way these large, heavy particles cause damage makes them more dangerous than other types of radiation. The ionizations they cause are very close together - they can release all their energy in a few cells. This results in more severe damage to cells and DNA.

These particles are emitted by certain unstable atoms such as hydrogen-3 tritium , carbon and strontium Beta particles are more penetrating than alpha particles, but are less damaging to living tissue and DNA because the ionizations they produce are more widely spaced.

They travel farther in air than alpha particles, but can be stopped by a layer of clothing or by a thin layer of a substance such as aluminum.