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Timeline of Epochs in Cosmology
The timeline of cosmological epochs outlines the formation and subsequent evolution of the Universe from the Big Bang (13.799 ± 0.021 billion years ago) to the present day. An epoch is a moment in time from which nature or situations change to such a degree that it marks the beginning of a new era or age. Times on this list are measured from the moment of the Big Bang.
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  • 21 Nov 2022
Topic Review
List of Largest Stars
Below is a list of the largest stars currently known, ordered by radius. The unit of measurement used is the radius of the Sun (approximately 695,700 km; 432,300 mi). The angular diameters of stars can be measured directly using stellar interferometry. Other methods can use lunar occultations or from eclipsing binaries, which can be used to test indirect methods of finding stellar radii. Only a few useful supergiant stars can be occulted by the Moon, including Antares A (Alpha Scorpii A). Examples of eclipsing binaries are Epsilon Aurigae (Almaaz), VV Cephei, and V766 Centauri (HR 5171). Angular diameter measurements can be inconsistent because the boundary of the very tenuous atmosphere (opacity) differs depending on the wavelength of light in which the star is observed. Uncertainties remain with the membership and order of the list, especially when deriving various parameters used in calculations, such as stellar luminosity and effective temperature. Often stellar radii can only be expressed as an average or be within a large range of values. Values for stellar radii vary significantly in different sources and for different observation methods. All the sizes stated in this list have various inaccuracies and may be disputed. This list is still a work in progress and various parameters are extremely disputed.
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Topic Review
Interference Reflection Microscopy
Interference reflection microscopy (IRM) is an optical microscopy technique that utilizes polarized light to form an image of an object on a glass surface. The intensity of the signal is a measure of proximity of the object to the glass surface. This technique can be used to study events at the cell membrane without the use of a (fluorescent) label in contrast to TIRF microscopy.
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Topic Review
Luch (Satellite)
The Luch (Russian: Луч; lit. Ray) Satellite Data Relay Network (SDRN), also referred to as Altair and Gelios, is a series of geosynchronous Russian relay satellites, used to transmit live TV images, communications and other telemetry from the Soviet/Russian space station Mir, the Russian Orbital Segment (ROS) of the International Space Station and other orbital spacecraft to the Earth, in a manner similar to that of the US Tracking and Data Relay Satellite System.
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Topic Review
Timeline of Physical Chemistry
The timeline of physical chemistry lists the sequence of physical chemistry theories and discoveries in chronological order.
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Topic Review
Plutoid
A plutoid or ice dwarf is a trans-Neptunian dwarf planet, i.e. a body orbiting beyond Neptune that is massive enough to be rounded in shape. The term plutoid was adopted by the International Astronomical Union (IAU) working group Committee on Small Bodies Nomenclature, but was rejected by the IAU working group Planetary System Nomenclature. The term plutoid is not widely used by astronomers, though ice dwarf is not uncommon. There are thought to be thousands of plutoids in the Solar System, although only four have been formally designated as such by the IAU. The IAU developed this category of astronomical objects as a consequence of its 2006 resolution defining the word "planet". The IAU's formal definition of "plutoid", announced 11 June 2008, is: In light of the difficulty of remotely ascertaining hydrostasis, the IAU only formally confers "dwarf planet" (and by extension, "plutoid") status to those bodies whose minimum estimated size is substantially greater than what is generally thought necessary to guarantee hydrostatic equilibrium. (As of 2009), Pluto, Eris, Haumea, and Makemake are the only objects officially recognized as plutoids, while upwards of seventy more bodies that currently lack formal recognition are thought likely to meet the definition, and can expect formal recognition at some time in the future. Alan Stern of the Southwest Research Institute believes the outer planets show signs of collisions with plutoids 1,000 to 2,000 kilometers in diameter: Uranus could have been tipped off its axis by a plutoid, and Triton, the largest moon of Neptune, is probably a captured plutoid from the Kuiper belt.
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Topic Review
Green Star
In astronomy, a green star is a white or blueish star that appears greenish in some viewing conditions (see § Psychology below). Under typical viewing conditions, there are no greenish stars, because the color of a star is more or less given by a black-body spectrum. However, there are a few stars that appear greenish to some observers, due to the viewing conditions, for example the optical 'illusion' that a red object can make nearby objects look greenish (and vice versa). Some multiple star systems, such as Antares, have a bright reddish star where this contrast makes other stars in the system seem greenish.
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Topic Review
Compact Fusion Reactor
The Lockheed Martin Compact Fusion Reactor (CFR) is a proposed nuclear fusion reactor project at Lockheed Martin’s Skunk Works. Its high-beta configuration, which implies that the ratio of plasma pressure to magnetic pressure is greater than or equal to 1 (compared to tokamak designs' 0.05), allows a compact fusion reactor (CFR) design and expedited development. The CFR chief designer and technical team lead, Thomas McGuire studied fusion as a source of space propulsion in response to a NASA desire to improve travel times to Mars.
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Topic Review
Mars (Planet)
Mars is the fourth planet from the Sun in our solar system and is named after Mars, the Roman god of war. Mars is also known as the "Red Planet" due to its reddish appearance when seen from Earth. The prefix areo-, from the Greek god of war, Ares, refers to Mars in the same way geo- refers to Earth. Until the first flyby of Mars by Mariner 4 in 1965, it was thought that Mars had channels of liquid water. Observations later showed that these channels do not exist. Still, of all the planets in our solar system other than Earth, Mars is the most likely to harbor liquid water, and perhaps life. Its rotational period and seasonal cycles are also similar to those of the Earth. It has the highest mountain in the solar system, Olympus Mons, the largest canyon in the solar system, Valles Marineris, and polar ice caps. Mars has two moons, Phobos and Deimos, which are small and oddly-shaped. These may be captured asteroids similar to 5261 Eureka, a Mars trojan asteroid. Mars can be seen from Earth by the naked eye. Its apparent magnitude reaches -2.9, a brightness surpassed only by Venus, the Moon, and the Sun. For much of the year, Jupiter may appear brighter to the naked eye than Mars. Mars is currently host to four orbiting spacecraft, more than any planet other than Earth. It is also home to the two Mars Exploration Rovers, Spirit and Opportunity.
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Topic Review
Osmium-182
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
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