Proxima Centauri

Red dwarfs in general are far too weak to be observable with the naked eye, and Proxima Centauri is no exception. It has an apparent magnitude of 11 while its absolute magnitude is a very weak 15.5. Seen from Alpha Centauri A or B, Proxima would be a 4.5 magnitude star. Based on the parallax of 772.33 ± 2.42 milliarcseconds measured by Hipparcos, Proxima Centauri is roughly 4.22 light years from Earth, or 270,000 times more distant than the Sun. Its closest neighbours are Alpha Centauri A and B (at 0.21 light years), t ...

See also:

Proxima Centauri, Proxima Centauri - Characteristics, Proxima Centauri - Traveling to Proxima Centauri, Proxima Centauri - In fiction and games

Read more here: » Proxima Centauri: Encyclopedia II - Proxima Centauri - Characteristics

Centaurus (Latin for centaur) was one of the 48 constellations listed by Ptolemy, and counts also among the 88 modern constellations. This southern constellation is one of the largest in the sky. Centaurus - Notable features. Centaurus is a bright constellation of the southern hemisphere. It contains Proxima Centauri, a red dwarf that is the nearest known star (other than the Sun) to Earth, as well as Alpha Centauri, which is a triple star to which Proxima Centauri is apparently gravitationall ...

Including:

• Centaurus - Notable features
• Centaurus - Notable deep sky objects
• Centaurus - History
• Centaurus - Mythology
• Centaurus - Stars

Read more here: » Centaurus: Encyclopedia - Centaurus

In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. Stellar temperatures can be classified by using Wien's displacement law; but this poses difficulties for distant stars. Stellar spectroscopy offers a way to classify stars according to their absorption lines; particular absorption lines can be observed only for a certain range of temperatures because only in that range are ...

Including:

• Stellar classification - Morgan-Keenan spectral classification
• Stellar classification - Spectral types
• Stellar classification - Spectral types for rare stars
• Stellar classification - White dwarf classifications
• Stellar classification - Yerkes spectral classification
• Stellar classification - UBV system

Read more here: » Stellar classification: Encyclopedia - Stellar classification

YZ Ceti is a red dwarf star in the constellation Cetus the whale. Although it is relatively close to the Sun at just over 12 light years, this star can not be seen with the naked eye. It is classified as a flare star that undergoes intermittent fluctuations in luminosity. YZ Ceti is only about 8.5% the mass of our Sun, and is normally less than 1/5000th as luminous. This star is located in unusually close proximity to Tau Ceti, a star of spectral class G8. The two are only about 0.72 light years apart, less than one-sixth the distance from the ...

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The astronomical unit (AU or au or a.u. or sometimes ua) is a unit of distance, approximately equal to the mean distance between Earth and Sun. The currently accepted value of the AU is 149 597 870 691 ± 30 metres (about 150 million kilometres or 93 million miles). The symbol "ua" is recommended by the Bureau International des Poids et Mesures [1], but in the United States and other anglophone countries the reverse usage is more common. The International Astronomical Union recommends "au" [2] and in ...

Including:

• Astronomical unit - The distance
• Astronomical unit - History
• Astronomical unit - Examples

Read more here: » Astronomical unit: Encyclopedia - Astronomical unit

Most stars are of nearly constant luminosity. Our own Sun is a good example of one which goes through relatively little variation in brightness (usually about 0.1% over an 11 year solar cycle). Many stars, however, undergo significant variations in luminosity, and these are known as variable stars. Variable stars may be either intrinsic or extrinsic. Intrinsic variable stars: stars where the variablility is being caused by changes in the physical properties of the stars themselves. This category can i ...

Including:

• Variable star - Variable star observations
• Variable star - Intrinsic variable stars
• Variable star - Pulsating variable stars
• Variable star - Eruptive variable stars
• Variable star - Cataclysmic variable stars
• Variable star - Extrinsic variable stars
• Variable star - Rotating variable stars
• Variable star - Eclipsing binaries
• Variable star - Planetary transits
• Variable star - Variable star nomenclature

Read more here: » Variable star: Encyclopedia - Variable star

A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. Unlike a planet, from which most light is reflected, a star emits light because of its intense heat. Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion. Stellar astronomy is the study of stars. Star - Star formation and evolution. Main article: stellar evolut ...

Including:

• Star - Star formation and evolution
• Star - Appearance and distribution of stars
• Star - Age and size of stars
• Star - Star classification
• Star - Naming of stars
• Star - Energy production
• Star - Nuclear fusion reaction pathways
• Star - Star mythology
• Star - Related lists

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Alpha Centauri (α Cen / α Centauri) is the brightest star system (a triple star system) in the southern constellation of Centaurus, and contains the fourth brightest star in the night sky, with an apparent visual magnitude of −0.01. It is famous in the Southern Hemisphere as the outermost “pointer” to the Southern Cross, but it is too far south to be visible in most of the northern hemisphere. To the naked eye, the two brightest components of the system are too close for the eye to ...

Including:

• Alpha Centauri - Names
• Alpha Centauri - System components
• Alpha Centauri - Possibility of planet formation
• Alpha Centauri - Sky appearance from Alpha Centauri
• Alpha Centauri - Apparent movement
• Alpha Centauri - Alpha Centauri in fiction

Read more here: » Alpha Centauri: Encyclopedia - Alpha Centauri

After Johannes Kepler discovered his Third Law, it was possible to build a scale model of the whole solar system, but without the scale. To fix the scale, it suffices to measure one distance within the solar system, e.g., the mean distance from the Earth to the Sun or astronomical unit (AU). When done by triangulation, this is referred to as the solar parallax, the difference in position of the Sun as seen from the Earth's centre and a point one Earth radius away, i.e., the angle subtended at the Sun by the Earth's mean radius. Knowin ...

See also:

Parallax, Parallax - Introduction, Parallax - Use in distance measurement, Parallax - Parallax of the human eye, Parallax - Binocular parallax, Parallax - Monocular parallax, Parallax - Parallax and measurement instruments, Parallax - Photogrammetric parallax, Parallax - Lunar parallax, Parallax - Solar parallax, Parallax - Stellar parallax, Parallax - Computation, Parallax - Dynamic or moving-cluster parallax, Parallax - The scale of the Universe, Parallax - Parallax as a metaphor, Parallax - Sources

Read more here: » Parallax: Encyclopedia II - Parallax - Solar parallax

An understanding of planetary habitability begins with stars, not planets themselves. While bodies that are generally Earth-like may be plentiful, it is just as important that their larger system be agreeable to life. Under the auspices of SETI's Project Phoenix, scientists Margaret Turnbull and Jill Tarter developed the "HabCat" (or Catalogue of Habitable Stellar Systems) in 2002. The catalogue was formed by winnowing the nearly 120,000 stars of the larger Hipparcos Catalogue into a core group of 17,000 "HabStars," and the selection criteri ...

See also:

Planetary habitability, Planetary habitability - Suitable star systems, Planetary habitability - Spectral class, Planetary habitability - A stable habitable zone, Planetary habitability - Low stellar variation, Planetary habitability - High metallicity, Planetary habitability - Binary systems, Planetary habitability - Planetary characteristics, Planetary habitability - Mass, Planetary habitability - Orbit and rotation, Planetary habitability - Geochemistry, Planetary habitability - Other considerations, Planetary habitability - The habitability of red dwarf planetary systems, Planetary habitability - Good Jupiters, Planetary habitability - The Galactic neighborhood, Planetary habitability - Notes

Read more here: » Planetary habitability: Encyclopedia II - Planetary habitability - Suitable star systems

In the diagram above (not to scale), S represents the Sun, and E the Earth at one point in its orbit. D is an object at a distance of one parsec from the Sun. By definition, the angle D is one arcsecond and the distance ES is one astronomical unit. By trigonometry, the distance SD is One astronomical unit is equal to approximately 1.49598×108 km, so The attoparsec (atto being the prefix indicating 10-18) is a unit humorously used by some hackers. It is approximately 3.1 c ...

See also:

Parsec, Parsec - Distances in parsecs, Parsec - How to calculate the value of a parsec, Parsec - Popular usage

Read more here: » Parsec: Encyclopedia II - Parsec - How to calculate the value of a parsec

Examples of types within these divisions are given below. Variable star - Pulsating variable stars. Main articles: Alpha Cygni variable, and [[{{{2}}}]], and [[{{{3}}}]],See also:

Variable star, Variable star - Variable star observations, Variable star - Intrinsic variable stars, Variable star - Pulsating variable stars, Variable star - Eruptive variable stars, Variable star - Cataclysmic variable stars, Variable star - Extrinsic variable stars, Variable star - Rotating variable stars, Variable star - Eclipsing binaries, Variable star - Planetary transits, Variable star - Variable star nomenclature

Read more here: » Variable star: Encyclopedia II - Variable star - Intrinsic variable stars

The term 'string theory' properly refers to both the 26-dimensional bosonic string theories and to the 10-dimensional superstring theories created by adding supersymmetry. Nowadays, 'string theory' usually refers to the supersymmetric variant while the earlier is given its full name, 'bosonic string theory'. While understanding the details of string and superstring theories requires considerable mathematical sophistication, some qualitative properties of quantum strings can be understood in a fairly intuitive fashion. For example, qua ...

See also:

String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - Popular culture, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Basic properties

The Three Stigmata of Palmer Eldritch - Back story. The Three Stigmata of Palmer Eldritch takes place some time in the twenty-first century. Under the authority of the United Nations, humankind has colonized every habitable planet and moon in the solar system. Life for most colonists is physically daunting and psychologically monotonous so the UN must draft individuals to colonize. Most colonists entertain themselves using Barbie-like “Perky Pat” dolls and the multitude accessories manufactured ...

See also:

The Three Stigmata of Palmer Eldritch, The Three Stigmata of Palmer Eldritch - Plot Synopsis, The Three Stigmata of Palmer Eldritch - Back story, The Three Stigmata of Palmer Eldritch - Storyline, The Three Stigmata of Palmer Eldritch - Religious themes, The Three Stigmata of Palmer Eldritch - Comparisons with Dick’s other work

Read more here: » The Three Stigmata of Palmer Eldritch: Encyclopedia II - The Three Stigmata of Palmer Eldritch - Plot Synopsis

Examples of types within these divisions are given below. Variable star - Pulsating variable stars. Main articles: Alpha Cygni variable, and [[]], and [[]], and [[]] ...

See also:

Variable star, Variable star - Variable star observations, Variable star - Intrinsic variable stars, Variable star - Pulsating variable stars, Variable star - Eruptive variable stars, Variable star - Cataclysmic variable stars, Variable star - Extrinsic variable stars, Variable star - Rotating variable stars, Variable star - Eclipsing binaries, Variable star - Planetary transits, Variable star - Variable star nomenclature

Read more here: » Variable star: Encyclopedia II - Variable star - Intrinsic variable stars

In the diagram above (not to scale), S represents the Sun, and E the Earth at one point in its orbit. D is an object at a distance of one parsec from the Sun. By definition, the angle D is one arcsecond and the distance ES is one astronomical unit. By trigonometry, the distance SD is One astronomical unit is equal to approximately 1.49598×108 km, so The attoparsec (atto being the prefix indicating 10-18) is a unit humorously used by some hackers. ...

See also:

Parsec, Parsec - Distances in parsecs, Parsec - How to calculate the value of a parsec, Parsec - Popular usage

Read more here: » Parsec: Encyclopedia II - Parsec - How to calculate the value of a parsec

Despite the belief by many that the existence of an alien technological civilization is not impossible, as of 2005 there has been no unambiguous evidence of intelligent extraterrestrial life. While many believe this is a vindication of the idea that we are alone in our galaxy (if not the universe) many theoreticians have proposed alternate explanations as to why the skies appear to be silent. Fermi paradox - They do not exist.... The simplest explanation is that we are alone in the galaxy. Several theories along these lines have b ...

See also:

Fermi paradox, Fermi paradox - Theorizing about extraterrestrial life: The basis of the paradox, Fermi paradox - Does it exist?, Fermi paradox - How common is it?: the Drake equation, Fermi paradox - Trying to resolve the paradox empirically: What we look for and how we look, Fermi paradox - The limits of searching, Fermi paradox - The dangers of anthropomorphism, Fermi paradox - What we might look for, Fermi paradox - How we've been looking, Fermi paradox - What we've found, Fermi paradox - Trying to resolve the paradox theoretically: Explaining the silence, Fermi paradox - They do not exist..., Fermi paradox - They do exist but..., Fermi paradox - Further reading and references, Fermi paradox - External links, Fermi paradox - References, Fermi paradox - Fictional treatment

Read more here: » Fermi paradox: Encyclopedia II - Fermi paradox - Trying to resolve the paradox theoretically: Explaining the silence

Presented like an aircraft recognition guide. This books contains neither novels nor short stories, only spacecraft descriptions. However, by reading the spaceship descriptions it is possible to imagine a classical science fiction story of an interstellar war between the good guys: the Terrans (from Earth) and the Alphans (from Alpha Centauri) and the bad guys: the Proximans (from Proxima Centauri). ...

See also:

Terran Trade Authority, Terran Trade Authority - Spacecraft 2000-2100 AD, Terran Trade Authority - Great Space Battles, Terran Trade Authority - SpaceWreck: Ghost Ships and Derelicts of Space, Terran Trade Authority - Starliners: Commercial Travel in 2200 AD

Read more here: » Terran Trade Authority: Encyclopedia II - Terran Trade Authority - Spacecraft 2000-2100 AD

The term 'string theory' properly refers to both the 26-dimensional bosonic string theories and to the 10-dimensional superstring theories created by adding supersymmetry. Nowadays, 'string theory' usually refers to the supersymmetric variant while the earlier is given its full name, 'bosonic string theory'. While understanding the details of string and superstring theories requires considerable mathematical sophistication, some qualitative properties of quantum strings can be understood in a fairly intuitive fashion. For example, qua ...

See also:

String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Basic properties

Stellar evolution - Geriatric low-mass stars. What happens after a low-mass star exhausts its hydrogen is not directly known: the universe is thought to be around 13.7 billion years old, which is less time (by several orders of magnitude, in some cases) than it takes for the fuel to be exhausted. Current theory is based on computer modelling. Some stars may fuse helium in core hot-spots, causing an unstable and uneven reaction as well as a heavy solar wind. In this case, the star will form no planet ...

See also:

Stellar evolution, Stellar evolution - Birth, Stellar evolution - The middle years of a star's life, Stellar evolution - Maturity, Stellar evolution - The later years and death of stars, Stellar evolution - Geriatric low-mass stars, Stellar evolution - Mid-sized stars, Stellar evolution - Supermassive stars

Read more here: » Stellar evolution: Encyclopedia II - Stellar evolution - The later years and death of stars