List of nearest bright stars

closestHD 120467nearest bright stars
This list of nearest bright stars is a table of stars found within 15 parsecs (48.9 light-years) of the Sun that have an absolute magnitude of +8.5 or brighter, which is approximately comparable to a listing of stars more luminous than a red dwarf. Right ascension and declination coordinates are for the epoch J2000. The distance measurements are based on the Hipparcos Catalogue and other astrometric data. In the event of a spectroscopic binary, the combined spectral type and absolute magnitude are listed in italics. The list is ordered by increasing distance. These stars are estimated to be within 32.6 light years of the Sun.

Brown dwarf

brown dwarfsbrown dwarvesPlanetar
Since then, over 1,800 brown dwarfs have been identified, even some very close to Earth like Epsilon Indi Ba and Bb, a pair of brown dwarfs gravitationally bound to a Sun-like star 12 light-years from the Sun, and Luhman 16, a binary system of brown dwarfs at 6.5 light-years from the Sun. The standard mechanism for star birth is through the gravitational collapse of a cold interstellar cloud of gas and dust. As the cloud contracts it heats due to the Kelvin–Helmholtz mechanism. Early in the process the contracting gas quickly radiates away much of the energy, allowing the collapse to continue. Eventually, the central region becomes sufficiently dense to trap radiation.

List of largest stars

largest known starslargest stars knownlargest stars
[[File:Star-sizes.jpg|500px|thumb|right|Relative sizes of the planets in the Solar System and several well-known stars:1. Mercury < Mars < Venus < Earth 2. Earth < Neptune < Uranus < Saturn < Jupiter 3. Jupiter < Proxima Centauri < Sun < Sirius A 4. Sirius A < Pollux < Arcturus < Aldebaran 5. Aldebaran < Rigel A < Antares A < Betelgeuse 6. Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris Below is an ordered list of the largest stars currently known by radius. The unit of measurement used is the radius of the Sun (approximately 1 solar radius).

Bayer designation

Bayerdesignationdesignations
Of the 88 modern constellations, there are at least 30 in which "Alpha" is not the brightest star, and four of those lack an alpha star altogether. (Constellations with no alpha include Vela and Puppis – both formerly part of Argo Navis, whose alpha is Canopus in Carina.) Orion provides a good example of Bayer's method. Bayer first designated Betelgeuse and Rigel, the two 1st-magnitude stars (those of magnitude 1.5 or less), as Alpha and Beta from north to south, with Betelgeuse (the shoulder) coming ahead of Rigel (the foot), even though the latter is usually the brighter. (Betelgeuse is a variable star and can at its maximum occasionally outshine Rigel.)

General relativity

general theory of relativityrelativitygeneral relativity theory
In the currently accepted models of stellar evolution, neutron stars of around 1.4 solar masses, and stellar black holes with a few to a few dozen solar masses, are thought to be the final state for the evolution of massive stars. Usually a galaxy has one supermassive black hole with a few million to a few billion solar masses in its center, and its presence is thought to have played an important role in the formation of the galaxy and larger cosmic structures. Astronomically, the most important property of compact objects is that they provide a supremely efficient mechanism for converting gravitational energy into electromagnetic radiation.

Red giant

red giant starred giantsred giant stars
The growth in planet mass could be partly due to accretion from stellar wind, although a much larger effect would be Roche lobe overflow causing mass-transfer from the star to the planet when the giant expands out to the orbital distance of the planet. Many of the well known bright stars are red giants, because they are luminous and moderately common. The red giant branch variable star Gamma Crucis is the nearest M class giant star at 88 light years. The K0 red giant branch star Arcturus is 36 light years away. In about 5 to 6 billion years, the Sun will have depleted the hydrogen fuel in its core.

Solar luminosity

luminosity of the SunSun's luminosityluminosity
Irradiance is defined as power per unit area, so the solar luminosity (total power emitted by the Sun) is the irradiance received at the Earth (solar constant) multiplied by the area of the sphere whose radius is the mean distance between the Earth and the Sun: where A is the unit distance (the value of the astronomical unit in metres) and k is a constant (whose value is very close to one) that reflects the fact that the mean distance from the Earth to the Sun is not exactly one astronomical unit. Sun. Solar mass. Solar radius. Nuclear fusion. Triple-alpha process. LISIRD: LASP Interactive Solar Irradiance Datacenter. Stellar Luminosity Calculator. Solar Luminosity.

Planet

planetsFormer classification of planetsplanetary-mass object
Around 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone, so the nearest would be expected to be within 12 light-years distance from Earth. The frequency of occurrence of such terrestrial planets is one of the variables in the Drake equation, which estimates the number of intelligent, communicating civilizations that exist in the Milky Way. There are exoplanets that are much closer to their parent star than any planet in the Solar System is to the Sun, and there are also exoplanets that are much farther from their star. Mercury, the closest planet to the Sun at 0.4 AU, takes 88 days for an orbit, but the shortest known orbits for exoplanets take only a few hours, e.g.

Astrometry

astrometricastrometricalastrometrist
Hipparchus compiled a catalogue with at least 850 stars and their positions. Hipparchus's successor, Ptolemy, included a catalogue of 1,022 stars in his work the Almagest, giving their location, coordinates, and brightness. In the 10th century, Abd al-Rahman al-Sufi carried out observations on the stars and described their positions, magnitudes and star color; furthermore, he provided drawings for each constellation, which are depicted in his Book of Fixed Stars. Ibn Yunus observed more than 10,000 entries for the Sun's position for many years using a large astrolabe with a diameter of nearly 1.4 metres.

Main sequence

main-sequencemain sequence dwarfmain-sequence star
Stars of luminosity class V belonged to the main sequence. In April 2018, astronomers reported the detection of the most distant "ordinary" (i.e., main sequence) star, named Icarus (formally, MACS J1149 Lensed Star 1), at 9 billion light-years away from Earth. When a protostar is formed from the collapse of a giant molecular cloud of gas and dust in the local interstellar medium, the initial composition is homogeneous throughout, consisting of about 70% hydrogen, 28% helium and trace amounts of other elements, by mass. The initial mass of the star depends on the local conditions within the cloud.

Large Magellanic Cloud

LargeLMCGreater Magellanic Cloud
Using this improved calibration, they find an absolute distance modulus of (m-M)_0 =18.41, or 48 kpc (~157,000 light-years). This distance has been confirmed by other authors. By cross-correlating different measurement methods, one can bound the distance; the residual errors are now less than the estimated size parameters of the LMC. The results of a study using late-type eclipsing binaries to determine the distance more accurately was published in the scientific journal Nature in March 2013. A distance of 49.97 kpc (163,000 light-years) with an accuracy of 2.2% was obtained.

Circumstellar disc

circumstellar diskcircumstellar diskscircumstellar
Circumprimary disc is one which orbits the primary (i.e. more massive) star of the binary system. This type of disc will form through accretion if any angular momentum is present in the infalling gas. Circumsecondary disc is one which orbits around the secondary (i.e. less massive) star of the binary star system. This type of disc will only form when a high enough level of angular momentum is present within the infalling gas. The amount of angular momentum required is dependent on the secondary-to-primary mass ratio. Circumbinary disc is one which orbits about both the primary and secondary stars.

Luyten 726-8

UV Ceti75 times in only 20 secondsBL Cet
The distance between the two stars varies from 2.1 to 8.8 AU. The Luyten 726-8 system is approximately 2.63 pc from Earth's Solar System, in the constellation Cetus, and is thus the seventh-closest star system to Earth. Its own nearest neighbor is Tau Ceti, 0.98 pc away from it. If R_v=+29 km/s then approximately 28,700 years ago Luyten 726-8 was at its minimal distance of 2.21 pc (7.2 ly) from the Sun. Luyten-726-8A was found to be a variable star and given the variable star designation BL Ceti. It is a red dwarf of spectral type M5.5e.

Very Large Telescope

VLTNACOVLTI
Unit Telescopes 1–4 are since known as Antu (Sun), Kueyen (Moon), Melipal (Southern Cross), and Yepun (Evening Star), respectively. Originally there was some confusion as to whether Yepun actually stands for the evening star Venus, because a Spanish-Mapuche dictionary from the 1940s wrongly translated Yepun as "Sirius". Although the four 8.2-metre Unit Telescopes can be combined in the VLTI, their observation time is spent mostly on individual observations, and are used for interferometric observations for a limited number of nights every year. However, the four smaller 1.8-metre ATs are available and dedicated to interferometry to allow the VLTI to operate every night.

Extinction (astronomy)

extinctionextinction factorinterstellar extinction
In general, however, this means that a star will have its brightness reduced by about a factor of 2 in the V-band viewed from a good night sky vantage point on earth for every kiloparsec (3,260 light years) it is farther away from us. The amount of extinction can be significantly higher than this in specific directions. For example, some regions of the Galactic Center are awash with obvious intervening dark dust from our spiral arm (and perhaps others) and themselves in a bulge of dense matter, causing as much as more than 30 magnitudes of extinction in the optical, meaning that less than 1 optical photon in 10 12 passes through.

Polaris

North Starpole starNorthern Star
Polaris, designated α Ursae Minoris (Latinized to Alpha Ursae Minoris, abbreviated Alpha UMi, α UMi), commonly the North Star or Pole Star, is the brightest star in the constellation of Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star. The revised Hipparcos parallax gives a distance to Polaris of about 433 light-years (133 parsecs), while calculations by other methods derive distances around 30% closer. Polaris is a triple star system, composed of the primary star, Polaris Aa (a yellow supergiant), in orbit with a smaller companion (Polaris Ab); the pair in orbit with Polaris B (discovered in August 1779 by William Herschel).

Star catalogue

star catalogNLTTLTT
Aitken's double star catalogue (1932) lists 17,180 double stars north of declination −30 degrees. Stephenson's General Catalogue of galactic Carbon stars is a catalogue of 7000+ carbon stars. The Gliese (later Gliese-Jahreiß) catalogue attempts to list all star systems within 20 pc of Earth ordered by right ascension (see the List of nearest stars). Later editions expanded the coverage to 25 pc. Numbers in the range 1.0–915.0 (Gl numbers) are from the second edition, which was The integers up to 915 represent systems which were in the first edition.

Algol

β PerseiAlgol BAlgol systems
Algol is about 92.8 light-years from the Sun, but about 7.3 million years ago it passed within 9.8 light-years of the Solar System and its apparent magnitude was about −2.5, which is considerably brighter than the star Sirius is today. Because the total mass of the Algol system is about 5.8 solar masses, at the closest approach this might have given enough gravity to perturb the Oort cloud of the Solar System somewhat and hence increase the number of comets entering the inner Solar System. However, the actual increase in net cometary collisions is thought to have been quite small. Beta Persei is the star's Bayer designation.

Stellar parallax

parallax shiftparallaxparallax method
Stellar parallax is the apparent shift of position of any nearby star (or other object) against the background of distant objects. Created by the different orbital positions of Earth, the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at exactly opposite sides of the Sun in its orbit, giving a baseline distance of about two astronomical units between observations. The parallax itself is considered to be half of this maximum, about equivalent to the observational shift that would occur due to the different positions of Earth and the Sun, a baseline of one astronomical unit (AU).

Herbig–Haro object

Herbig–HaroHerbig Haro Be starHerbig-Haro objects
At these distances the outflow is divergent, with fanning out at an angle in the range of 10−30°, but it becomes increasingly collimated at distances of tens to hundreds of astronomical units from the source, as its expansion is constrained. The jets also carry away the excess angular momentum resulting from accretion of material onto the star, which would otherwise cause the star to rotate rapidly and disintegrate. When these jets collide with the interstellar medium, they give rise to the small patches of bright emission which comprise HH objects.

Circumstellar habitable zone

habitable zonehabitable zoneshabitability zone
For reference, the average distance from the Sun of some major bodies within the various estimates of the habitable zone are: Mercury, 0.39 AU; Venus, 0.72 AU; Earth, 1.00 AU; Mars, 1.52 AU; Vesta, 2.36 AU; Ceres, 2.77 AU; Jupiter, 5.20 AU; Saturn, 9.58 AU. Astronomers use stellar flux and the inverse-square law to extrapolate circumstellar habitable zone models created for the Solar System to other stars. For example, although the Solar System has a circumstellar habitable zone centered at 1.34 AU from the Sun, a star with 0.25 times the luminosity of the Sun would have a habitable zone centered at \sqrt{0.25}, or 0.5, the distance from the star, corresponding to a distance of 0.67 AU.

Interstellar medium

interstellar gasinterstellarinterstellar matter
The apparent rifts that can be seen in the band of the Milky Way – a uniform disk of stars – are caused by absorption of background starlight by molecular clouds within a few thousand light years from Earth. Far ultraviolet light is absorbed effectively by the neutral components of the ISM. For example, a typical absorption wavelength of atomic hydrogen lies at about 121.5 nanometers, the Lyman-alpha transition. Therefore, it is nearly impossible to see light emitted at that wavelength from a star farther than a few hundred light years from Earth, because most of it is absorbed during the trip to Earth by intervening neutral hydrogen. The ISM is usually far from thermodynamic equilibrium.

Supernova

supernovaecore-collapse supernovasupernovas
Because these supernovae arise from dim, common white dwarf stars in binary systems, it is likely that a supernova that can affect the Earth will occur unpredictably and in a star system that is not well studied. The closest known candidate is IK Pegasi (see below). Recent estimates predict that a Type II supernova would have to be closer than eight parsecs (26 light-years) to destroy half of the Earth's ozone layer, and there are no such candidates closer than about 500 light years. The next supernova in the Milky Way will likely be detectable even if it occurs on the far side of the galaxy.

Space Interferometry Mission

SIMSIM Lite Astrometric ObservatorySpace Interferometry Mission (SIM)
The observatory would have been able to measure the small wobbles in stars and detect the planets causing them down to one Earth mass at distances up to 33 light years (10 parsecs) from the Sun. 65 stars for planets down to one Earth mass, in scaled 1 AU orbits, OR. 149 stars for planets down to two Earth masses, in scaled 1 AU orbits, OR. 239 stars for planets down to three Earth masses, in scaled 1 AU orbits. NASA's PlanetQuest. Palomar Observatory. List of NASA cancellations. "Fringes: Space Interferometry Mission Newsletter" Index. SIM Lite Astrometric Observatory (formerly SIM PlanetQuest), from NASA. SIM PlanetQuest Mission Profile by NASA's Solar System Exploration.