Gamma-ray detectors typically contain densely packed crystal blocks. Gamma-ray wavelengths are so short that they can pass through the space within the atoms of a detector. Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes.
Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum. Credit: NASA/DOE/International LAT Team SOURCES OF GAMMA RAYS Of course, when sunlight passes through a lot of atmosphere as is the case with sunrises and sunsets, even more blue light is scattered and a much greater percentage of the longest wavelength (red) light makes it to our eyes.Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Most UV is absorbed by stratospheric ozone (above 10km) and most IR is absorbed by water vapor and other molecules with non - zero dipole moments. Though it does not affect what our eyes see, all x-ray and gamma ray radiation is filtered out before it comes close to the ground. This allows the brain to perceive color from the image with a little less blue – yellow. In addition, all wavelengths of visible light passing through our atmosphere are attenuated so that the light that reaches our eyes does not immediately saturate the cone receptors. Since shorter wavelength blue light is scattered more efficiently than longer wavelength red light, we lose some of the blue tint of the sun as sunlight passes through the atmosphere. Here on Earth, the atmosphere plays a role in the color of the sun. Our brains then integrate these signals into a perceived white color. Our eyes which have three color cone cell receptors, report to the brain that each color receptor is completely saturated with significant colors being received at all visible wavelengths. If we were above the atmosphere, say on the International Space Station and looked at the sun (through our filtered visor), the sun would appear white! Why? Because though the sun emits strongest in the green part of the spectrum, it also emits strongly in all the visible colors – red through blue (400nm to 600nm). If we use the relationship found by Max Planck, E = hf (that is Energy = the Planck Constant times the Frequency) and convert the solar irradiance into photon counts, the spectral signature across visible wavelengths is much flatter and the sun is perceived as more yellow. I must note here another spectral signature from the sun, the photon flux. A lower surface temperature, and our sun’s spectrum might peak in the yellow or orange or even red part of the spectrum. A higher surface temperature would result in a shorter maximum wavelength and our sun might peak in the blue or violet part of the spectrum (or even the ultra violet!). So one might say that the sun is blue-green! This maximum radiation frequency is governed by the sun’s surface temperature, around 5,800K. But, as can be seen in the image above, it emits most of its energy around 500 nm, which is close to blue-green light. So, the sun actually emits energy at all wavelengths from radio to gamma ray. The flares also accelerate charged particle plasmas to high speeds resulting in radio emission. During very hot, explosive, high energy solar flare events, the sun emits huge amounts of x-ray and gamma ray radiation as well, up to over 100 MeV energies and up to 10 32 ergs of energy over only a few seconds or tens of seconds! These massive solar flares are huge explosions in the sun’s atmosphere caused by the sudden release of magnetic field energy and tend to occur near solar maximum. For our sun, this black body curve or “Plank Function” is a smooth almost bell shaped curve involving electromagnetic (EM) radiation at many different wavelengths from very long infrared to very short ultraviolet wavelengths. A black body spectrum is the continuum of radiation at many different wavelengths that is emitted by any body with a temperature above absolute zero.
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