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List Of Unsolved Problems In Astronomy
This article is a list of notable unsolved problems in astronomy. Problems may be theoretical or experimental. Theoretical problems result from inability of current theories to explain observed phenomena or experimental results. Experimental problems result from inability to test or investigate a proposed theory. Other problems involve unique events or occurrences that have not repeated themselves with unclear causes. Planetary astronomy The Solar System * Orbiting bodies and rotation: ** Are there any non-dwarf planets beyond Neptune? ** Why do extreme trans-Neptunian objects have elongated orbits? ** The rotation rate of Saturn: *** Why does the magnetosphere of Saturn rotate at a rate close to that at which the planet's clouds rotate? *** What is the rotation rate of Saturn's deep interior? * Satellite geomorphology: ** What is the origin of the chain of high mountains that closely follows the equator of Saturn's moon, Iapetus? *** Are the mountains the remnant of hot and fa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Unsolved Problems
List of unsolved problems may refer to several notable List of conjectures, conjectures or open problems in various academic fields: Natural sciences, engineering and medicine * List of unsolved problems in astronomy, Unsolved problems in astronomy * List of unsolved problems in biology, Unsolved problems in biology * List of unsolved problems in chemistry, Unsolved problems in chemistry * List of unsolved problems in geoscience, Unsolved problems in geoscience * List of unsolved problems in medicine, Unsolved problems in medicine * List of unsolved problems in neuroscience, Unsolved problems in neuroscience * List of unsolved problems in physics, Unsolved problems in physics Mathematics, statistics and information sciences * List of unsolved problems in mathematics, Unsolved problems in mathematics * List of unsolved problems in statistics, Unsolved problems in statistics * List of unsolved problems in computer science, Unsolved problems in computer science * List of unsolved prob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Cycle
The Solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a periodic 11-year change in the Sun's activity measured in terms of Modern Maximum, variations in the number of observed sunspots on the Sun's surface. Over the period of a solar cycle, levels of solar radiation and ejection of solar material, the number and size of sunspots, solar flares, and coronal loops all exhibit a synchronized fluctuation from a Solar minimum, period of minimum activity to a Solar maximum, period of a maximum activity back to a period of minimum activity. The magnetic field of the Sun flips during each solar cycle, with the flip occurring when the solar cycle is near its maximum. After two solar cycles, the Sun's magnetic field returns to its original state, completing what is known as a Hale cycle. This cycle has been observed for centuries by changes in the Sun's appearance and by terrestrial phenomena such as aurora but was not clearly identified un ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleogenesis
Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium (called 'metals' by astrophysicists) remains small (few percent), so that the universe still has approximately the same composition. Stars fu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P-nuclei
p-nuclei (''p'' stands for proton-rich) are certain proton-rich, naturally occurring isotopes of some elements between selenium and mercury inclusive which cannot be produced in either the s- or the r-process. Definition The classical, ground-breaking works of Burbidge, Burbidge, Fowler and Hoyle (1957) and of A. G. W. Cameron (1957) showed how the majority of naturally occurring nuclides beyond the element iron can be made in two kinds of neutron capture processes, the s- and the r-process. Some proton-rich nuclides found in nature are not reached in these processes and therefore at least one additional process is required to synthesize them. These nuclei are called p-nuclei. Since the definition of the p-nuclei depends on the current knowledge of the s- and r-process (see also nucleosynthesis), the original list of 35 p-nuclei may be modified over the years, as indicated in the Table below. For example, it is recognized today that the abundances of 152Gd and 164Er cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the ''progenitor'', either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula. The peak optical luminosity of a supernova can be comparable to that of an entire galaxy before fading over several weeks or months. The last supernova directly observed in the Milky Way was Kepler's Supernova in 1604, appearing not long after Tycho's Supernova in 1572, both of which were visible to the naked eye. The supernova remnant, remnants of more recent supernovae have been found, and observations of supernovae in other galaxies suggest they occur in the Milky Way on average about three times every century. A supernova in the Milky Way would almost certainly be observable through mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Initial Mass Function
In astronomy, the initial mass function (IMF) is an empirical function that describes the initial distribution of masses for a population of stars during star formation. IMF not only describes the formation and evolution of individual stars, it also serves as an important link that describes the formation and evolution of galaxies. The IMF is often given as a probability density function (PDF) that describes the probability for a star to have a certain mass during its formation. It differs from the ''present-day mass function'' (PDMF), which describes the current distribution of masses of stars, such as red giants, white dwarfs, neutron stars, and black holes, after some time of evolution away from the main sequence stars and after a certain amount of mass loss. Since there are not enough young clusters of stars available for the calculation of IMF, PDMF is used instead and the results are extrapolated back to IMF. IMF and PDMF can be linked through the "stellar creation function ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geomagnetic Storm
A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere that is driven by interactions between the magnetosphere and large-scale transient Plasma (physics), plasma and magnetic field structures that originate on or near the Sun. The structures that produce geomagnetic storms include interplanetary coronal mass ejections (CME) and corotating interaction regions (CIR). The former often originate from solar active regions, while the latter originate at the boundary between high- and low-speed streams of solar wind. The frequency of geomagnetic storms increases and decreases with the sunspot cycle. During solar maximum, solar maxima, geomagnetic storms occur more often, with the majority driven by CMEs. When these structures reach Earth, the increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth's magnetic field and transfers an increased energy into th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Storm
A solar storm is a disturbance on the Sun, which can emanate outward across the heliosphere, affecting the entire Solar System, including Earth and its magnetosphere, and is the cause of space weather in the short-term with long-term patterns comprising space climate. Types Solar storms include: * Solar flare, a large explosion in the Sun's atmosphere caused by tangling, crossing or reorganizing of magnetic field lines * Coronal mass ejection (CME), a massive burst of plasma from the Sun, sometimes associated with solar flares * Geomagnetic storm, the interaction of the Sun's outburst with Earth's magnetic field * Solar particle event (SPE), proton or solar energetic particle, energetic particle (SEP) See also * List of solar storms * Aurora, a luminous phenomenon induced by ionization and excitation of constituents of a planet's upper atmosphere * Heliophysics, the scientific study of the Sun and region of space affected by the Sun * Magnetic cloud, a transient disturbance in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geomagnetic Storms
A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere that is driven by interactions between the magnetosphere and large-scale transient plasma and magnetic field structures that originate on or near the Sun. The structures that produce geomagnetic storms include interplanetary coronal mass ejections (CME) and corotating interaction regions (CIR). The former often originate from solar active regions, while the latter originate at the boundary between high- and low-speed streams of solar wind. The frequency of geomagnetic storms increases and decreases with the sunspot cycle. During solar maxima, geomagnetic storms occur more often, with the majority driven by CMEs. When these structures reach Earth, the increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth's magnetic field and transfers an increased energy into the magnetosphere. Both intera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coronal Mass Ejections
A coronal mass ejection (CME) is a significant ejection of plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established. If a CME enters interplanetary space, it is sometimes referred to as an interplanetary coronal mass ejection (ICME). ICMEs are capable of reaching and colliding with Earth's magnetosphere, where they can cause geomagnetic storms, aurorae, and in rare cases damage to electrical power grids. The largest recorded geomagnetic perturbation, resulting presumably from a CME, was the solar storm of 1859. Also known as the ''Carrington Event'', it disabled parts of the newly created United States telegraph network, starting fires and electrically shocking some telegraph operators. Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space Weather
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 of Earth, atmosphere (troposphere and stratosphere). 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. History For many centuries, the effects of space weather were noticed, but not understood. Displays of aurora (astronomy), auroral light have long been observed at high latitudes. Beginnings In 1724, George Graham (clockmaker), George Graham reported that the needle of a magnetic compass was regularly deflected from magnetic north over the course of each day. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Reconnection
Magnetic reconnection is a physical process occurring in electrically conducting Plasma (physics), plasmas, in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration. Magnetic reconnection involves plasma flows at a substantial fraction of the Alfvén wave speed, which is the fundamental speed for mechanical information flow in a magnetized plasma. The concept of magnetic reconnection was developed in parallel by researchers working in solar physics and in the interaction between the solar wind and magnetized planets. This reflects the bidirectional nature of reconnection, which can either disconnect formerly connected magnetic fields or connect formerly disconnected magnetic fields, depending on the circumstances. Ron Giovanelli is credited with the first publication invoking magnetic energy release as a potential mechanism for particle acceleration in Solar flare, solar flares. Giovanelli propose ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
