The Difference between Solar and Terrestrial Radiation

Both the sun and the earth naturally produce large amounts of radiation. The difference between solar and terrestrial radiation is that all purely terrestrial radiation comes from fission of radioactive elements, while all solar radiation comes from the fusion of hydrogen into helium. This difference in the source of radiation leads to other differences in the type of radiation.

Solar radiation

Fusion in the sun’s core produces huge amounts of energy, but most of it takes thousands of years to reach the surface of the sun. The gamma rays which are released by fusion are continually absorbed and then released again at lower energy levels, so they can travel only about 1/2 inch at a time until they escape the sun’s surface into vacuum. By that time, they have lost too much energy to be gamma rays.

Sunshine is made up of electromagnetic radiation across most of the electromagnetic spectrum except gamma rays. This includes X-rays, ultraviolet rays, infrared rays, microwaves, radio waves, and visible light. Most solar energy output is in the form of visible light.

In addition to electromagnetic radiation, solar radiation also consists of the loose electrons and other charged particles which make up the solar wind. Loose electrons and positrons, also known as beta rays, make up most of the solar wind, along with lone protons, or hydrogen nuclei which have been stripped of all electrons. A few alpha particles, or stripped helium nuclei, are also included in the solar wind. However, most loose protons, by far, have an extra-solar origin. Between 10% and 12% of all cosmic rays which bombard the Earth consist of alpha particles, and nearly all of the rest are hydrogen nuclei.

All solar X-rays are blocked by the highest parts of the Earth’s atmosphere. Most ultraviolet light is blocked by the ozone layer. Most infrared rays, microwaves, and shortwave radio waves are absorbed in the Earth’s stratosphere. All long wave radio waves bounce off the ionosphere. Charged particles are caught and deflected by the Earth’s magnetic field.

Most solar radiation which reaches the Earth’s surface is in the form of visible light. A few infrared rays which are close to the wavelength of visible light reach the Earth’s surface to be felt as heat. Some shortwave radio waves also reach the Earth’s surface.

During high intensity solar flares and coronal mass ejections (CME), so much solar radiation is released that the magnetosphere may be overwhelmed and the ionosphere itself is affected. This can disrupt radar and other radio transmissions, as well as creating brilliant auroras near the magnetic poles. In extreme cases, the highly magnetized solar plasma released during a strong CME can damage communications satellites, and the associated auroral current can short out electrical grids.

Terrestrial radiation

All naturally occurring terrestrial radiation is the direct byproduct of nuclear fission. It is commonly known as background radiation. Naturally occurring terrestrial radiation accounts for 74% of all ionizing radiation exposure: 55% from radon gas, 8% from other external sources, and 11% from internal sources. Cosmic sources, including the sun, account for another 8% of ionizing radiation exposure. The remainder is from man-made sources.

In the atmosphere, the most common radioactive element is radon gas. In the ground, sources of radioactivity vary from location to location, depending on the local geology. Uranium and thorium are common under old rock formations, such as the Canadian Shield. Radium has been found in unusually high quantities in many hot springs.

Potassium-40, lead-210, and carbon-14 are naturally consumed as part of the food source. These elements can be found inside the human body from birth.

Nuclear fission produces alpha and beta particles, as well as photons in various parts of the electromagnetic spectrum from gamma rays down to visible light. The exact breakdown of byproducts and energies depends on which element isotope is decaying, and sometimes on the exact reaction or chain reaction. However, the energies involved are usually much lower than those from solar radiation.

All terrestrial radiation originally came from stellar radiation

Every element on Earth, including uranium and other radioactive elements, came originally from hydrogen fusion in a star. The sun is a Population I star, rich in heavy elements which it has not itself produced. These elements are believed to come from other novas and supernovas. In stars which are larger than the sun, the process of fusion combines light elements other than hydrogen into heavier elements. The largest stars of all produce the heaviest elements, just before they explode into supernovas.