According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. Examples include Aldebaran, in the constellation Taurus, and Arcturus. The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... 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. ... Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–750 nm. ... Giant star is a star that has stopped fusing hydrogen in its core. ... Aldebaran from the Arabic (الدبران al-dabarān) meaning the follower, (α Tau / α Tauri / Alpha Tauri) is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. ... |10 Tau]] | stardistance = 44. ... Arcturus (α Boo / α Boötis / Alpha Boötis) (IPA: ) is the brightest star in the constellation Boötes, and the third brightest star in the night sky, with a visual magnitude of −0. ...

Overview

Red giants are stars of 1000 times the volume of the Sun which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core. Since the inert helium core has no source of energy of its own, it contracts and heats up, and its gravity compresses the hydrogen in the layer immediately above it, thus causing it to fuse faster. This in turn causes the star to become more luminous (from 1,000 to 10,000 times brighter) and expand; the degree of expansion outstrips the increase in luminosity, thus causing the effective temperature to decrease. In stars massive enough to ignite helium fusion, an analogous process occurs when central helium is exhausted and the star switches to fusing helium in a shell, although with the additional complication that in many cases hydrogen fusion will continue in a shell at lesser depth — this puts stars onto the asymptotic giant branch.^[1][2] The decrease in surface temperature shifts the star's visible light output to the red — hence red giant. Stars of spectral types O through K are believed to become red giants (or supergiants in the case of O and B stars).^{[citation needed]} The Sun (Latin: Sol) is the star at the center of the Solar System. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... The effective temperature of a star is the temperature of a black body with the same luminosity (L) as the star and is defined according to the Stefan-Boltzman law L = sigma T_{eff}^{4}. The effective temperature of our Sun is around 5,800 kelvins (K) and correspond to... Helium fusion is a kind of nuclear fusion, with the nuclei involved being helium. ... A period of Stellar evolution undertaken by all low to intermediate mass stars (0. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ...

Comparison between red giants and the Sun

Very low mass stars are thought to be fully convective^[3] and thus may not accumulate an inert core of helium, and thus may exhaust all of their fuel without ever becoming red giants.^[4] Such stars are commonly referred to as red dwarfs. Image File history File links Redgiants. ... Image File history File links Redgiants. ... This article describes the British science fiction comedy television series. ...

If the star is less than 2.57 solar masses, the addition of helium to the core by shell hydrogen fusing will cause a helium flash—a rapid burst of helium fusing in the core, after which the star will commence a brief period of helium fusing before beginning another ascent of the red giant branch. Stars more massive than 2.5 solar masses enter the helium fusing phase of their lives much more smoothly. The core helium fusing phase of a star's life is called the horizontal branch in metal-poor stars, so named because these stars lie on a nearly horizontal line in the Hertzsprung-Russell diagram of many star clusters. Metal-rich helium-fusing stars do not lie on a horizontal branch, but instead lie in a clump (the red clump) in the Hertzsprung-Russell diagram.^{[citation needed]} General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... A Helium flash is the sudden beginning of helium burning in the core of intermediate mass stars, or on the surface of an accreting white dwarf star. ... The horizontal branch (HB) is a stage of stellar evolution which immediately follows the red giant branch. ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... The Red Clump is a region on the Hertzsprung-Russell diagram occupied primarily by metal-rich red giant stars. ...

Actually, such stars are not big red spheres with a sharp limbs (when one is close to it) as displayed on many images. Due to the very low density such stars may not have a sharp photosphere but a star body which gradually transfers into a 'corona'.^{[citation needed]} The photosphere of an astronomical object is the region at which the optical depth becomes one for a photon of wavelength equal to 5000 angstroms. ... A corona is a type of plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ...

When the Sun has exhausted its supply of hydrogen to fuse it will swell into the Red Giant phase. The size of the current Sun (now in the main sequence) is here compared to its estimated size during its red giant phase.

Image File history File links Sun_Red_Giant2. ... Image File history File links Sun_Red_Giant2. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

The Sun as a red giant

The Sun is expected to become a red giant in about five billion years. It is calculated that the Sun will become sufficiently large to engulf the current orbits of some of the solar system's inner planets, including Earth.^[5][6][7] However, the gravitational pull of the Sun will have weakened by then due to its loss of mass, and all planets but Mercury will escape to a wider orbit. That said, Earth's biosphere will be destroyed as the Sun gets brighter while its hydrogen supply becomes depleted. The extra solar energy will cause the oceans to evaporate to space, causing Earth's atmosphere to become temporarily similar to that of Venus, before the atmosphere is also lost.^[8] The Sun (Latin: Sol) is the star at the center of the Solar System. ... Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ... In the solar system the inner planets are the solid planets nearest the Sun: Mercury, Venus, Earth and Mars. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... This article is about the planet. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... A false-color composite of global oceanic and terrestrial photoautotroph abundance, from September 1997 to August 2000. ... Adjectives: Venusian or (rarely) Cytherean Atmosphere Surface pressure: 9. ...

See also

• Stellar evolution
• Blue giant
• Red dwarf star
• Supergiant
• Red supergiant
• White dwarf

In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... In astronomy, a blue giant is a star with a spectral type of O or B and class of III (giant). ... This article is about red dwarfs, the type of star. ... Supergiants are the most massive stars. ... Betelgeuse, viewed from a distance of 8 AU. By comparison, this is our own Sun, and how it would appear when viewed from the same distance. ... This article or section does not adequately cite its references or sources. ...

References

For the Manfred Mann album, see 2006 (album). ... January 21 is the 21st day of the year in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... February 16 is the 47th day of the year in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... For the Manfred Mann album, see 2006 (album). ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... Georgia State University (GSU) is an urban research university in the heart of downtown Atlanta, Georgia, USA. Founded in 1913, it serves over 28,000[1] students, and is one of the University System of Georgias four research universities. ... For the Manfred Mann album, see 2006 (album). ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... shelby was here 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... June 2 is the 153rd day of the year in the Gregorian calendar (154th in leap years), with 212 days remaining. ... For the Manfred Mann album, see 2006 (album). ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... For the Manfred Mann album, see 2006 (album). ... December 29 is the 363rd day of the year (364th in leap years) in the Gregorian calendar, with 2 days remaining. ... 1997 (MCMXCVII) was a common year starting on Wednesday of the Gregorian calendar. ... June 13 is the 164th day of the year in the Gregorian calendar (165th in leap years), with 201 days remaining. ... 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... January 23 is the 23rd day of the year in the Gregorian calendar. ...

External links

• Measurements of the frequency of starspots on red giant stars