Query: [S]unspot activity on the surface of our star has dropped to a new low.

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Sun <=SEP=> The Sun is the star at the center of the Solar System . It is a nearly perfect sphere of hot plasma , with internal convective motion that generates a magnetic field via a dynamo process . It is by far the most important source of energy for life on Earth . Its diameter is about 109 times that of Earth , and its mass is about 330,000 times that of Earth , accounting for about 99.86 % of the total mass of the Solar System .  About three quarters of the Sun 's mass consists of hydrogen ( ~ 73 % ) ; the rest is mostly helium ( ~ 25 % ) , with much smaller quantities of heavier elements , including oxygen , carbon , neon , and iron .   The Sun is a G-type main-sequence star ( G2V ) based on its spectral class . As such , it is informally referred to as a yellow dwarf . It formed approximately 4.6 billionAll numbers in this article are short scale . One billion is 109 , or 1,000,000,000 . years ago from the gravitational collapse of matter within a region of a large molecular cloud . Most of this matter gathered in the center , whereas the rest flattened into an orbiting disk that became the Solar System . The central mass became so hot and dense that it eventually initiated nuclear fusion in its core . It is thought that almost all stars form by this process .   The Sun is roughly middle-aged ; it has not changed dramatically for more than four billion years , and will remain fairly stable for more than another five billion years . After hydrogen fusion in its core has diminished to the point at which it is no longer in hydrostatic equilibrium , the core of the Sun will experience a marked increase in density and temperature while its outer layers expand to eventually become a red giant . It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus , and render Earth uninhabitable .   The enormous effect of the Sun on Earth has been recognized since prehistoric times , and the Sun has been regarded by some cultures as a deity . The synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar , which is the predominant calendar in use today .

Proxima Centauri <=SEP=> Proxima Centauri or Alpha Centauri C is a red dwarf , a small low-mass star , about 4.25 light-years from the Sun in the constellation of Centaurus . It was discovered in 1915 by the Scottish astronomer Robert Innes , the Director of the Union Observatory in South Africa , and is the nearest-known star to the Sun . With an apparent magnitude of 11.05 , it is too faint to be seen with the naked eye . Proxima Centauri forms a third component of the Alpha Centauri binary star system , currently with a separation of about AU and an orbital period of 550,000 years .   Because of Proxima Centauri 's proximity to Earth , its angular diameter can be measured directly . It is about one-seventh the diameter of the Sun . It has a mass about an eighth of the Sun 's mass , and its average density is about 40 times that of the Sun . Although it has a very low average luminosity , Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity . The star 's magnetic field is created by convection throughout the stellar body , and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun . The mixing of the fuel at Proxima Centauri 's core through convection and its relatively low energy-production rate mean that it will be a main-sequence star for another four trillion years , or nearly 300 times the current age of the universe .   In 2016 , the European Southern Observatory announced the discovery of Proxima b , a planet orbiting the star at a distance of roughly 0.05 AU with an orbital period of approximately 11.2 Earth days . Its estimated mass is at least 1.3 times that of the Earth . The equilibrium temperature of Proxima b is estimated to be within the range where water could exist as liquid on its surface , thus placing it within the habitable zone of Proxima Centauri , although because Proxima Centauri is a red dwarf and a flare star , whether it could support life is disputed .  Previous searches for orbiting companions had ruled out the presence of brown dwarfs and supermassive planets .

Star <=SEP=> A star is a luminous sphere of plasma held together by its own gravity . The nearest star to Earth is the Sun . Many other stars are visible to the naked eye from Earth during the night , appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth . Historically , the most prominent stars were grouped into constellations and asterisms , the brightest of which gained proper names . Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations . However , most of the stars in the Universe , including all stars outside our galaxy , the Milky Way , are invisible to the naked eye from Earth . Indeed , most are invisible from Earth even through the most powerful telescopes .   For at least a portion of its life , a star shines due to thermonuclear fusion of hydrogen into helium in its core , releasing energy that traverses the star 's interior and then radiates into outer space . Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star 's lifetime , and for some stars by supernova nucleosynthesis when it explodes . Near the end of its life , a star can also contain degenerate matter . Astronomers can determine the mass , age , metallicity ( chemical composition ) , and many other properties of a star by observing its motion through space , its luminosity , and spectrum respectively . The total mass of a star is the main factor that determines its evolution and eventual fate . Other characteristics of a star , including diameter and temperature , change over its life , while the star 's environment affects its rotation and movement . A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung -- Russell diagram ( H -- R diagram ) . Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined .   A star 's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen , along with helium and trace amounts of heavier elements . When the stellar core is sufficiently dense , hydrogen becomes steadily converted into helium through nuclear fusion , releasing energy in the process . The remainder of the star 's interior carries energy away from the core through a combination of radiative and convective heat transfer processes . The star 's internal pressure prevents it from collapsing further under its own gravity . A star with mass greater than 0.4 times the Sun 's will expand to become a red giant when the hydrogen fuel in its core is exhausted . In some cases , it will fuse heavier elements at the core or in shells around the core . As the star expands it throws a part of its mass , enriched with those heavier elements , into the interstellar environment , to be recycled later as new stars . Meanwhile , the core becomes a stellar remnant : a white dwarf , a neutron star , or if it is sufficiently massive a black hole .   Binary and multi-star systems consist of two or more stars that are gravitationally bound and generally move around each other in stable orbits . When two such stars have a relatively close orbit , their gravitational interaction can have a significant impact on their evolution . Stars can form part of a much larger gravitationally bound structure , such as a star cluster or a galaxy .