A Moreton wave or Moreton-Ramsey wave is the chromospheric signature of a large-scale solar coronal shock wave. Described as a kind of solar "tsunami", they are generated by solar flares, they are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank, Harry E. Ramsey, an observer who spotted them in 1959 at The Sacramento Peak Observatory, he discovered them in time-lapse photography of the chromosphere in the light of the Balmer alpha transition. There were few follow-up studies for decades; the 1995 launch of the Solar and Heliospheric Observatory led to observation of coronal waves, which cause Moreton waves. Moreton waves were a research topic again; the reality of Moreton waves has been confirmed by the two STEREO spacecraft. They observed a 100,000-km-high wave of hot plasma and magnetism, moving at 250 km/s, in conjunction with a big coronal mass ejection in February 2009. Moreton measured the waves propagating at a speed of 500–1500 km/s. Yutaka Uchida interpreted Moreton waves as MHD fast mode shock waves propagating in the corona.
He links them to type II radio bursts, which are radio-wave discharges created when coronal mass ejections accelerate shocks. Moreton waves can be observed in the Hα band. Solar transition region Spicule Solar prominence Gravity wave Helioseismology Asteroseismology OSO 8 More of Moreton's papers can be found here. "Have you heard the Sun?" - many recordings of solar radio emissions including a solar flare shockfront
Solar transition region
The solar transition region is a region of the Sun's atmosphere, between the chromosphere and corona. It is visible from space using telescopes, it is important because it is the site of several unrelated but important transitions in the physics of the solar atmosphere: Below, gravity tends to dominate the shape of most features, so that the Sun may be described in terms of layers and horizontal features. Below, most of the helium is not ionized, so that it radiates energy effectively; this has a profound effect on the equilibrium temperature. Below, the material is opaque to the particular colors associated with spectral lines, so that most spectral lines formed below the transition region are absorption lines in infrared, visible light, near ultraviolet, while most lines formed at or above the transition region are emission lines in the far ultraviolet and X-rays; this makes radiative transfer of energy within the transition region complicated. Below, gas pressure and fluid dynamics dominate the motion and shape of structures.
The transition region itself is not well studied in part because of the computational cost and complexity of Navier–Stokes combined with electrodynamics. Helium ionization is important because it is a critical part of the formation of the corona: when solar material is cool enough that the helium within it is only ionized, the material cools by radiation effectively via both black-body radiation and direct coupling to the helium Lyman continuum; this condition holds at the top of the chromosphere, where the equilibrium temperature is a few tens of thousands of kelvins. Applying more heat causes the helium to ionize at which point it ceases to couple well to the Lyman continuum and does not radiate nearly as effectively; the temperature jumps up to nearly one million kelvin, the temperature of the solar corona. This phenomenon is called the temperature catastrophe and is a phase transition analogous to boiling water to make steam. If the amount of heat being applied to coronal material is reduced, the material rapidly cools down past the temperature catastrophe to around one hundred thousand kelvin, is said to have condensed.
The transition region consists of material around this temperature catastrophe. The transition region is visible in far-ultraviolet images from the TRACE spacecraft, as a faint nimbus above the dark surface of the Sun and the corona; the nimbus surrounds FUV-dark features such as solar prominences, which consist of condensed material, suspended at coronal altitudes by the magnetic field. Moreton wave Coronal hole Spicule Animated explanation of the Transition Region. Animated explanation of the temperature of the Transition Region
Spicule (solar physics)
In solar physics, a spicule is a dynamic jet of about 500 km diameter in the chromosphere of the Sun. It moves upwards at about 20 km/s from the photosphere, they were discovered in 1877 by Father Angelo Secchi of the Observatory of Roman Collegium in Rome. Spicules last for about 15 minutes, they are associated with regions of high magnetic flux. They rise at a rate of 20 km/s and can reach several thousand kilometers in height before collapsing and fading away. There are about 300,000 active spicules at any one time on the Sun's chromosphere, amounting to about 1% of the Sun's surface. An individual spicule reaches 3,000–10,000 km altitude above the photosphere. Bart De Pontieu, Robert Erdélyi and Stewart James hypothesised in 2004 that spicules formed as a result of P-mode oscillations in the Sun's surface, sound waves with a period of about five minutes that causes the Sun's surface to rise and fall at several hundred meters per second. Magnetic flux tubes that tilted away from the vertical can focus and guide the rising material up into the solar atmosphere to form a spicule.
There is still however some controversy about the issue in the solar physics community. De Pontieu, B. Erdélyi, R. and James, S: Solar chromospheric spicules from the leakage of photospheric oscillations and flows In: Nature. 430/2004, p. 536–539, ISSN 0028-0836 NASA Astronomy Picture of the Day: Spicules: Jets on the Sun
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is used as an estimate of a body's surface temperature when the body's emissivity curve is not known; when the star's or planet's net emissivity in the relevant wavelength band is less than unity, the actual temperature of the body will be higher than the effective temperature. The net emissivity may be low due to surface or atmospheric properties, including greenhouse effect; the effective temperature of a star is the temperature of a black body with the same luminosity per surface area as the star and is defined according to the Stefan–Boltzmann law FBol = σTeff4. Notice that the total luminosity of a star is L = 4πR2σTeff4, where R is the stellar radius; the definition of the stellar radius is not straightforward. More rigorously the effective temperature corresponds to the temperature at the radius, defined by a certain value of the Rosseland optical depth within the stellar atmosphere.
The effective temperature and the bolometric luminosity are the two fundamental physical parameters needed to place a star on the Hertzsprung–Russell diagram. Both effective temperature and bolometric luminosity depend on the chemical composition of a star; the effective temperature of our Sun is around 5780 kelvins. Stars have a decreasing temperature gradient; the "core temperature" of the Sun—the temperature at the centre of the Sun where nuclear reactions take place—is estimated to be 15,000,000 K. The color index of a star indicates its temperature from the cool—by stellar standards—red M stars that radiate in the infrared to the hot blue O stars that radiate in the ultraviolet; the effective temperature of a star indicates the amount of heat that the star radiates per unit of surface area. From the warmest surfaces to the coolest is the sequence of stellar classifications known as O, B, A, F, G, K, M. A red star could be a tiny red dwarf, a star of feeble energy production and a small surface or a bloated giant or supergiant star such as Antares or Betelgeuse, either of which generates far greater energy but passes it through a surface so large that the star radiates little per unit of surface area.
A star near the middle of the spectrum, such as the modest Sun or the giant Capella radiates more energy per unit of surface area than the feeble red dwarf stars or the bloated supergiants, but much less than such a white or blue star as Vega or Rigel. To find the effective temperature of a planet, it can be calculated by equating the power received by the planet to the known power emitted by a blackbody of temperature T. Take the case of a planet at a distance D from the star, of luminosity L. Assuming the star radiates isotropically and that the planet is a long way from the star, the power absorbed by the planet is given by treating the planet as a disc of radius r, which intercepts some of the power, spread over the surface of a sphere of radius D; the calculation assumes the planet reflects some of the incoming radiation by incorporating a parameter called the albedo. An albedo of 1 means that all the radiation is reflected, an albedo of 0 means all of it is absorbed; the expression for absorbed power is then: P a b s = L r 2 4 D 2 The next assumption we can make is that the entire planet is at the same temperature T, that the planet radiates as a blackbody.
The Stefan–Boltzmann law gives an expression for the power radiated by the planet: P r a d = 4 π r 2 σ T 4 Equating these two expressions and rearranging gives an expression for the effective temperature: T = L 16 π σ D 2 4 Note that the planet's radius has cancelled out of the final expression. The effective temperature for Jupiter from this calculation is 88 K and 51 Pegasi b is 1,258 K. A better estimate of effective temperature for some planets, such as Jupiter, would need to include the internal heating as a power input; the actual temperature depends on atmosphere effects. The actual temperature from spectroscopic analysis for HD 209458 b is 1,130 K, but the effective temperature is 1,359 K; the internal heating within Jupiter raises the effective temperature to about 152 K. The surface temperature of a planet can be estimated by modifying the effective-temperature calculation to account for emissivity and temperature variation; the area of the planet that absorbs the power from the star is Aabs, some fraction of the total surface area Atotal = 4πr2, where r is the radius of the planet.
This area intercepts some of the power, spread over the surface of a sphere of radius D. We allow the planet to reflect some of the incoming radiation by incorporating a parameter a called the albedo. An albedo of 1 means that all the radiation is reflected, an albedo
The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research. NASA was established in 1958; the new agency was to have a distinctly civilian orientation, encouraging peaceful applications in space science. Since its establishment, most US space exploration efforts have been led by NASA, including the Apollo Moon landing missions, the Skylab space station, the Space Shuttle. NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the Space Launch System and Commercial Crew vehicles; the agency is responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA science is focused on better understanding Earth through the Earth Observing System. From 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1.
In the early 1950s, there was challenge to launch an artificial satellite for the International Geophysical Year. An effort for this was the American Project Vanguard. After the Soviet launch of the world's first artificial satellite on October 4, 1957, the attention of the United States turned toward its own fledgling space efforts; the US Congress, alarmed by the perceived threat to national security and technological leadership, urged immediate and swift action. On January 12, 1958, NACA organized a "Special Committee on Space Technology", headed by Guyford Stever. On January 14, 1958, NACA Director Hugh Dryden published "A National Research Program for Space Technology" stating: It is of great urgency and importance to our country both from consideration of our prestige as a nation as well as military necessity that this challenge be met by an energetic program of research and development for the conquest of space... It is accordingly proposed that the scientific research be the responsibility of a national civilian agency...
NACA is capable, by rapid extension and expansion of its effort, of providing leadership in space technology. While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency was created in February 1958 to develop space technology for military application. On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA; when it began operations on October 1, 1958, NASA absorbed the 43-year-old NACA intact. A NASA seal was approved by President Eisenhower in 1959. Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA. A significant contributor to NASA's entry into the Space Race with the Soviet Union was the technology from the German rocket program led by Wernher von Braun, now working for the Army Ballistic Missile Agency, which in turn incorporated the technology of American scientist Robert Goddard's earlier works. Earlier research efforts within the US Air Force and many of ARPA's early space programs were transferred to NASA.
In December 1958, NASA gained control of the Jet Propulsion Laboratory, a contractor facility operated by the California Institute of Technology. The agency's leader, NASA's administrator, is nominated by the President of the United States subject to approval of the US Senate, reports to him or her and serves as senior space science advisor. Though space exploration is ostensibly non-partisan, the appointee is associated with the President's political party, a new administrator is chosen when the Presidency changes parties; the only exceptions to this have been: Democrat Thomas O. Paine, acting administrator under Democrat Lyndon B. Johnson, stayed on while Republican Richard Nixon tried but failed to get one of his own choices to accept the job. Paine was confirmed by the Senate in March 1969 and served through September 1970. Republican James C. Fletcher, appointed by Nixon and confirmed in April 1971, stayed through May 1977 into the term of Democrat Jimmy Carter. Daniel Goldin was appointed by Republican George H. W. Bush and stayed through the entire administration of Democrat Bill Clinton.
Robert M. Lightfoot, Jr. associate administrator under Democrat Barack Obama, was kept on as acting administrator by Republican Donald Trump until Trump's own choice Jim Bridenstine, was confirmed in April 2018. Though the agency is independent, the survival or discontinuation of projects can depend directly on the will of the President; the first administrator was Dr. T. Keith Glennan appointed by Republican President Dwight D. Eisenhower. During his term he brought together the disparate projects in American space development research; the second administrator, James E. Webb, appointed by President John F. Kennedy, was a Democrat who first publicly served under President Harry S. Truman. In order to implement the Apollo program to achieve Kennedy's Moon la
A corona is an aura of plasma that surrounds the Sun and other stars. The Sun's corona extends millions of kilometres into outer space and is most seen during a total solar eclipse, but it is observable with a coronagraph; the word corona is a Latin word meaning "crown", from the Ancient Greek κορώνη. Spectroscopy measurements indicate strong ionization in the corona and a plasma temperature in excess of 1,000,000 kelvins, much hotter than the surface of the Sun. Light from the corona comes from the same volume of space; the K-corona is created by sunlight scattering off free electrons. The F-corona is created by sunlight bouncing off dust particles, is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the E-corona is due to spectral emission lines produced by ions that are present in the coronal plasma. In 1724, French-Italian astronomer Giacomo F. Maraldi recognized that the aura visible during a solar eclipse belongs to the Sun not to the Moon.
In 1809, Spanish astronomer José Joaquín de Ferrer coined the term'corona'. Based in his own observations of the 1806 solar eclipse at Kinderhook, de Ferrer proposed that the corona was part of the Sun and not of the Moon. English astronomer Norman Lockyer identified the first element unknown on Earth in the Sun's chromosphere, called helium. French astronomer Jules Jenssen noted that the size and shape of the corona changes with the sunspot cycle. In 1930, Bernard Lyot invented the coronograph, which allows to see the corona without a total eclipse. In 1952, American astronomer Eugene Parker proposed that the solar corona might be heated by myriad tiny'nanoflares', miniature brightenings resembling solar flares that would occur all over the surface of the Sun; the high temperature of the Sun's corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a unknown element, "coronium". Instead, these spectral features have since been explained by ionized iron.
Bengt Edlén, following the work of Grotrian, first identified the coronal spectral lines in 1940 as transitions from low-lying metastable levels of the ground configuration of ionised metals. The sun's corona is much hotter than the visible surface of the Sun: the photosphere's average temperature is 5800 kelvins compared to the corona's one to three million kelvins; the corona is 10−12 times as dense as the photosphere, so produces about one-millionth as much visible light. The corona is separated from the photosphere by the shallow chromosphere; the exact mechanism by which the corona is heated is still the subject of some debate, but possibilities include induction by the Sun's magnetic field and magnetohydrodynamic waves from below. The outer edges of the Sun's corona are being transported away due to open magnetic flux and hence generating the solar wind; the corona is not always evenly distributed across the surface of the sun. During periods of quiet, the corona is more or less confined to the equatorial regions, with coronal holes covering the polar regions.
However, during the Sun's active periods, the corona is evenly distributed over the equatorial and polar regions, though it is most prominent in areas with sunspot activity. The solar cycle spans 11 years, from solar minimum to the following minimum. Since the solar magnetic field is continually wound up due to the faster rotation of mass at the sun's equator, sunspot activity will be more pronounced at solar maximum where the magnetic field is more twisted. Associated with sunspots are coronal loops, loops of magnetic flux, upwelling from the solar interior; the magnetic flux pushes the hotter photosphere aside, exposing the cooler plasma below, thus creating the dark sun spots. Since the corona has been photographed at high resolution in the X-ray range of the spectrum by the satellite Skylab in 1973, later by Yohkoh and the other following space instruments, it has been seen that the structure of the corona is quite varied and complex: different zones have been classified on the coronal disc.
The astronomers distinguish several regions, as described below. Active regions are ensembles of loop structures connecting points of opposite magnetic polarity in the photosphere, the so-called coronal loops, they distribute in two zones of activity, which are parallel to the solar equator. The average temperature is between two and four million kelvins, while the density goes from 109 to 1010 particle per cm3. Active regions involve all the phenomena directly linked to the magnetic field, which occur at different heights above the Sun's surface: sunspots and faculae, occur in the photosphere, spicules, Hα filaments and plages in the chromosphere, prominences in the chromosphere and transition region, flares and coronal mass ejections happen in the corona and chromosphere. If flares are violent, they can perturb the photosphere and generate a Moreton wave. On the contrary, quiescent prom
Solar eclipse of August 11, 1999
A total solar eclipse occurred on 11 August 1999 with an eclipse magnitude of 1.029. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby or obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide; the path of the Moon's shadow began in the Atlantic Ocean and, before noon, was traversing the southern United Kingdom, northern France, Luxembourg, southern Germany, Slovenia, Croatia and northern FR Yugoslavia. The eclipse's maximum was at 11:03 UTC at 45.1°N 24.3°E / 45.1. It was the first total eclipse visible from Europe since 22 July 1990, the first visible in the United Kingdom since 29 June 1927; because of the high population densities in areas of the path, this was one of the most-viewed total solar eclipses in human history.
Some of the organized eclipse-watching parties along the path of totality set up video projectors on which people could watch the Moon's shadow as it raced towards them. There was substantial coverage on International TV stations of the progress of the eclipse shadow; the Moon's shadow was observed from the Russian Mir space station. The BBC concentrated its coverage efforts on the first landfall of the shadow across the western end of Cornwall, packed with an extraordinary number of visitors, although Cornwall did not have nearly as many as expected leading to many specially organised events being left with small attendance; the veteran amateur astronomer and eclipse-watcher Patrick Moore was brought in to head a live programme, but the eclipse was clouded out. BBC One produced a special version of their Balloon Idents for the event; the BBC did not have a presence at Goonhilly on the Lizard Peninsula, one of the few places in Cornwall where the clouds parted just in time for the total eclipse to be visible.
Some of the best viewing conditions were to be had mid-Channel, where ferries were halted in calm conditions to obtain an excellent view. Hundreds of people who gathered on the island of Alderney experienced the event. There was extensive cloud in Perranporth which parted just in time, allowing the large crowd that filled the beach and hillsides to witness the event. A gathering of several thousand people at the airport in Soissons, on the path of totality, were denied all but a few fleeting glimpses of the eclipse through the overcast sky; the clouds cleared just a few minutes after the eclipse. In contrast, the overcast sky in Amiens, where thousands had gathered, cleared only minutes before the eclipse began. Further inland, viewing conditions were perfect at Vouziers, a French country town gridlocked by Belgian cars from day-visitors; the patchy cloud covering cleared a short time. Some photos from Vouziers were used on the subsequent BBC Sky at Night programme; the San Francisco Exploratorium featured a live webcast from a crowded town square in Amasya, Turkey.
Doordarshan, the national TV channel in India, broadcast live coverage from Srikakulam, hosted by the TV personality Mona Bhattacharya. A Bulgarian Air Force MiG-21 two-seater was used by the Bulgarian Academy of Sciences to study the solar corona; the MiG-21, flying at 1600–1700 km/h at an altitude of 13,000 m, was able to stay in the Moon's umbra for 6 min. The photographer, an air force pilot, used two film cameras, both fitted with 200 mm lenses and infrared filters, one Digital8 video camera. Hungary's most popular tourist destination, Lake Balaton and its surrounding area, fell into the path of the eclipse which made the area more popular for that day; the motorway leading there was so crowded, many people had to watch the eclipse while caught in a traffic jam. One French and two British Concordes followed the eclipse with tourists on board; the BBC was filming one of its episodes for its TV series Airport that day and, during the show, resident press officers Russell Clisby and Steve Meller took photographs of the eclipse at Heathrow Airport, as well as Aeroflot supervisor Jeremy Spake witnessing the eclipse on a special charter flight.
RTS, the national public broadcaster of Serbia, urged people to remain inside, citing dangers to public health. This caused the streets of all Serbian cities and villages to be deserted during the eclipse, with many opting to watch it on TV instead; the BMJ a month after the eclipse reported only 14 cases of eye damage from improper viewing of the eclipse, a number lower than feared. In one of the most serious cases the patient had looked at the Sun without eye protection for twenty minutes, but overall the public health campaign had succeeded; this eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats every 177 days and 4 hours at alternating nodes of the Moon's orbit; this solar eclipse is a part of Saros cycle 145, repeating every 18 years, 11 days, 8 hours, containing 77 events. The series started with a partial solar eclipse on January 4, 1639, reached