The ionosphere is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth. Travel through this layer also impacts GPS signals, resulting in effects such as deflection in their path and delay in the arrival of the signal.
The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV. The composition of the solar wind plasma also includes a mixture of particle species found in the solar plasma: trace amounts of heavy ions and atomic nuclei of elements such as carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron. There are also rarer traces of some other nuclei and isotopes such as phosphorus, titanium, chromium, and nickel's isotopes 58Ni, 60Ni, and 62Ni. Superimposed with the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The boundary separating the corona from the solar wind is called the Alfvén surface.
The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the thermosphere thus constitutes the larger part of the ionosphere. Taking its name from the Greek θερμός meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to 2,000 °C (3,630 °F) or more. Radiation causes the atmospheric particles in this layer to become electrically charged, enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375 mi) above sea level, the atmosphere turns into space, although, by the judging criteria set for the definition of the Kármán line (100 km), most of the thermosphere is part of space. The border between the thermosphere and exosphere is known as the thermopause.
A solar flare is a relatively intense, localized emission of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other eruptive solar phenomena. The occurrence of solar flares varies with the 11-year solar cycle.
The Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetosphere. Earth has two such belts, and sometimes others may be temporarily created. The belts are named after James Van Allen, who published an article describing the belts in 1958.
Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the varying conditions within the Solar System and its heliosphere. This includes the effects of the solar wind, especially on the Earth's magnetosphere, ionosphere, thermosphere, and exosphere. Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere. The term "space weather" was first used in the 1950s and popularized in the 1990s. Later, it prompted research into "space climate", the large-scale and long-term patterns of space weather.
Nozomi was a Japanese Mars orbiter that failed to reach Mars due to electrical failure. It was constructed by the Institute of Space and Astronautical Science, University of Tokyo and launched on July 4, 1998, at 03:12 JST with an on-orbit dry mass of 258 kg and 282 kg of propellant. The Nozomi mission was terminated on December 31, 2003.
The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes near the Sun in its highly elliptical orbit. As the comet warms, parts of it sublimate; this gives a comet a diffuse appearance when viewed through telescopes and distinguishes it from stars. The word coma comes from the Greek κόμη (kómē), which means "hair" and is the origin of the word comet itself.
Helios-A and Helios-B are a pair of probes that were launched into heliocentric orbit to study solar processes. As a joint venture between German Aerospace Center (DLR) and NASA, the probes were launched from Cape Canaveral Air Force Station, Florida, on December 10, 1974, and January 15, 1976, respectively.
The magnetosphere of Saturn is the cavity created in the flow of the solar wind by the planet's internally generated magnetic field. Discovered in 1979 by the Pioneer 11 spacecraft, Saturn's magnetosphere is the second largest of any planet in the Solar System after Jupiter. The magnetopause, the boundary between Saturn's magnetosphere and the solar wind, is located at a distance of about 20 Saturn radii from the planet's center, while its magnetotail stretches hundreds of Saturn radii behind it.
Extreme ultraviolet radiation or high-energy ultraviolet radiation is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths shorter than the hydrogen Lyman-alpha line from 121 nm down to the X-ray band of 10 nm. By the Planck–Einstein equation the EUV photons have energies from 10.26 eV up to 124.24 eV where we enter the X-ray energies. EUV is naturally generated by the solar corona and artificially by plasma, high harmonic generation sources and synchrotron light sources. Since UVC extends to 100 nm, there is some overlap in the terms.
A plasma wave instrument (PWI), also known as a plasma wave receiver, is a device capable of detecting vibrations in outer space plasma and transforming them into audible sound waves or air vibrations that can be heard by the human ear. This instrument was pioneered by then-University of Iowa physics professor, Donald Gurnett. Plasma wave instruments are commonly employed on space probes such as GEOTAIL, Polar, Voyager I and II, and Cassini–Huygens.
The magnetosphere of Jupiter is the cavity created in the solar wind by Jupiter's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System, and by volume the largest known continuous structure in the Solar System after the heliosphere. Wider and flatter than the Earth's magnetosphere, Jupiter's is stronger by an order of magnitude, while its magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the Pioneer 10 spacecraft in 1973.
The Van Allen Probes, formerly known as the Radiation Belt Storm Probes (RBSP), were two robotic spacecraft that were used to study the Van Allen radiation belts that surround Earth. NASA conducted the Van Allen Probes mission as part of the Living With a Star program. Understanding the radiation belt environment and its variability has practical applications in the areas of spacecraft operations, spacecraft system design, mission planning and astronaut safety. The probes were launched on 30 August 2012 and operated for seven years. Both spacecraft were deactivated in 2019 when they ran out of fuel. They are expected to deorbit during the 2030s.
The Astronomical Netherlands Satellite was a space-based X-ray and ultraviolet telescope. It was launched into Earth orbit on 30 August 1974 at 14:07:39 UTC in a Scout rocket from Vandenberg Air Force Base, United States. The mission ran for 20 months until June 1976, and was jointly funded by the Netherlands Institute for Space Research (NIVR) and NASA. ANS was the first Dutch satellite, and the Main Belt asteroid 9996 ANS was named after it. ANS reentered Earth's atmosphere on June 14, 1977.
This is an index to articles about terms used in discussion of radio propagation.
A comet tail and coma are visible features of a comet when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them.
Energetic Neutral Atom (ENA) imaging is a technology used to create global images of otherwise invisible phenomena in the magnetospheres of planets and throughout the heliosphere.
Explorer 55, also known as AE-E, was a NASA scientific satellite belonging to the Atmosphere Explorer series launched on 20 November 1975 from Cape Canaveral Air Force Station (CCAFS) aboard a Thor-Delta 2910 launch vehicle.
Professor Ebun Oni (21 May 1935 - 2 December 2021) known in early life as Ebun Adegbohungbe and later as Ebun Adefunmilyo Oni was a Nigerian geophysicist, university teacher and writer. One of Nigeria's first indigenous female scientists, she became a world-renowned specialist in geophysics through her numerous journal publications, and an eminent scientist and educator at the University of Ibadan in Nigeria.
