{"id":9044,"date":"2025-10-31T21:12:55","date_gmt":"2025-10-31T21:12:55","guid":{"rendered":"https:\/\/www.star-facts.com\/?p=9044"},"modified":"2026-03-01T20:29:47","modified_gmt":"2026-03-01T20:29:47","slug":"alfirk-beta-cephei","status":"publish","type":"post","link":"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/","title":{"rendered":"Alfirk (Beta Cephei)"},"content":{"rendered":"<p>Alfirk, Beta Cephei (\u03b2 Cep), is a triple star system located approximately 690 light-years away in the northern constellation <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a>. With an apparent magnitude of 3.23, it is the third brightest point of light in Cepheus, after <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> (Alpha Cephei) and <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (Gamma Cephei). The primary component in the system serves as the prototype for a class of variable stars known as the Beta Cephei variables.<\/p>\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#Star_system\" >Star system<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#Beta_Cephei_variables\" >Beta Cephei variables<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#North_Star\" >North Star<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#Facts\" >Facts<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#Name\" >Name<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#Location\" >Location<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/#Constellation\" >Constellation<\/a><\/li><\/ul><\/nav><\/div>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"Star_system\"><\/span>Star system<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Beta Cephei is a triple star composed of a binary pair, Beta Cephei A, and a companion, Beta Cephei B. The two components of the binary star are designated Beta Cephei Aa and Beta Cephei Ab. Beta Cephei Aa, the primary component in the system, is officially known as Alfirk.<\/p>\n<p>Alfirk is a hot blue subgiant star of the spectral type B1 IV. Older sources classify it as a B-type giant. The star has a mass of 7.4 solar masses and a radius 7.22 times that of the Sun. With an effective temperature of around 23,600 K, it is 20,000 times more luminous than the Sun. It spins with a projected rotational velocity of 28 km\/s, taking around 51 days to complete a revolution.<\/p>\n<p>Alfirk has an estimated age of only 8.7 million years. Even though it is still a very young star, it is approaching the end of its main sequence lifetime. It has evolved quickly because of its high mass.<\/p>\n<p>The close companion, Beta Cephei Ab, is believed to be a B6-type star with a mass of 5 solar masses. It is classified as a Be star, a fast-spinning B-type main sequence star with a gaseous disk of material expelled as a result of the rapid rotation.<\/p>\n<p>Beta Cephei Aa and Ab have an orbital period of 29616.54 \u00b1 1.36 days (81 years). The system has a semi-major axis of 206.96 \u00b1 0.53 milliarcseconds.<\/p>\n<p>Beta Cephei Ab was first resolved using speckle interferometry with a 200-inch telescope in 1972. It was <a href=\"https:\/\/ui.adsabs.harvard.edu\/abs\/1972ApJ...173L...1G\/abstract\">discovered<\/a> by a team led by D. Y. Gezari of the Department of Earth and Space Sciences, State University of New York at Stony Brook. The astronomers reported the presence of a companion at a separation of 0.255 \u00b1 0.010 arcseconds and proposed that tidal interaction may contribute to the variation mechanism of Beta Cephei.<\/p>\n<p>The more distant companion, Beta Cephei B, is a white main sequence star with the stellar classification A2 V. With an apparent visual magnitude of 7.8, it is invisible to the unaided eye. The star is separated by 13.6 arcseconds from Alfirk, corresponding to a physical distance of 2,840 astronomical units (AU).<\/p>\n<p>Alfirk serves as the prototype for a class of pulsating variable stars called the Beta Cephei variables. Its brightness varies from magnitude 3.16 to 3.27 with a period of 4.57 hours. The star appears the brightest when it is the smallest and hottest.<\/p>\n<div id=\"attachment_9055\" style=\"width: 710px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-9055\" class=\"size-full wp-image-9055\" src=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Alfirk-Beta-Cephei.webp\" alt=\"alfirk star,beta cephei\" width=\"700\" height=\"500\" srcset=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Alfirk-Beta-Cephei.webp 700w, https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Alfirk-Beta-Cephei-300x214.webp 300w\" sizes=\"auto, (max-width: 700px) 100vw, 700px\" \/><p id=\"caption-attachment-9055\" class=\"wp-caption-text\">Alfirk (Beta Cephei), image credit: ESO\/Digitized Sky Survey 2 (<a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY 4.0<\/a>)<\/p><\/div>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"Beta_Cephei_variables\"><\/span>Beta Cephei variables<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Beta Cephei variables are stars that show small rapid brightness variations due to pulsations of their surfaces. These pulsations are linked with unusual properties of iron in the stars\u2019 interiors, where temperatures reach 200,000 K. The stars vary in brightness by 0.01 to 0.3 magnitudes with periods of 2.4 to 7.2 hours. The variations are greater \u2013 up to 1 magnitude \u2013 at ultraviolet wavelengths.<\/p>\n<p>The pulsations of \u03b2 Cephei variables are driven by the kappa mechanism and p-mode pulsations. The letter kappa (\u03ba) indicates the radiative opacity at any depth of a star\u2019s atmosphere. In \u03b2 Cep stars, the opacity of iron increases at a depth where the temperatures reach 200,000 K. This results in a buildup of energy, which causes increased pressure that pushes the layer out in a cycle that repeats itself over several hours.<\/p>\n<p>Beta Cephei stars are typically hot blue stars of the spectral type B. They are not to be mistaken for Cepheid variables, a class of pulsating supergiants named after the class prototype Delta Cephei. The pulsations in Beta Cephei variables are driven by iron opacity whereas in Cepheid variables they are caused by the opacity of doubly ionized helium.<\/p>\n<p>Beta Cephei variables are sometimes called Beta Canis Majoris stars, after the brighter <a href=\"https:\/\/www.star-facts.com\/mirzam\/\">Mirzam<\/a> (Beta Canis Majoris) in the constellation <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/canis-major-constellation\/\">Canis Major<\/a>.<\/p>\n<p>Other than <a href=\"https:\/\/www.star-facts.com\/mirzam\/\">Mirzam<\/a> and Alfirk, bright examples of this class include <a href=\"https:\/\/www.star-facts.com\/hadar\/\">Hadar<\/a> (Beta Centauri) and <a href=\"https:\/\/www.star-facts.com\/epsilon-centauri\/\">Epsilon Centauri<\/a> in the constellation <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/centaurus-constellation\/\">Centaurus<\/a>, <a href=\"https:\/\/www.star-facts.com\/spica\/\">Spica<\/a> (Alpha Virginis) in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/virgo-constellation\/\">Virgo<\/a>, <a href=\"https:\/\/www.star-facts.com\/mimosa\/\">Mimosa<\/a> (Beta Crucis) and <a href=\"https:\/\/www.star-facts.com\/imai\/\">Imai<\/a> (Delta Crucis) in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/crux-constellation\/\">Crux<\/a>, <a href=\"https:\/\/www.star-facts.com\/shaula\/\">Shaula<\/a> (Lambda Scorpii), <a href=\"https:\/\/www.star-facts.com\/alniyat-sigma-scorpii\/\">Alniyat<\/a> (Sigma Scorpii) and <a href=\"https:\/\/www.star-facts.com\/kappa-scorpii\/\">Kappa Scorpii<\/a> in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/scorpius-constellation\/\">Scorpius<\/a>, <a href=\"https:\/\/www.star-facts.com\/alpha-lupi\/\">Uridim<\/a> (Alpha Lupi) and Delta Lupi in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/lupus-constellation\/\">Lupus<\/a>, Alpha Muscae in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/musca-constellation\/\">Musca<\/a>, <a href=\"https:\/\/www.star-facts.com\/algenib\/\">Algenib<\/a> (Gamma Pegasi) in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/pegasus-constellation\/\">Pegasus<\/a>, Epsilon Persei in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/perseus-constellation\/\">Perseus<\/a>, and Theta Ophiuchi in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/ophiuchus-constellation\/\">Ophiuchus<\/a>.<\/p>\n<div id=\"attachment_9056\" style=\"width: 1290px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-9056\" class=\"size-full wp-image-9056\" src=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Beta-Cephei-variables-HR-diagram.webp\" alt=\"beta cephei variables on the hertzsprung russell diagram\" width=\"1280\" height=\"961\" srcset=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Beta-Cephei-variables-HR-diagram.webp 1280w, https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Beta-Cephei-variables-HR-diagram-300x225.webp 300w, https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Beta-Cephei-variables-HR-diagram-1024x769.webp 1024w, https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Beta-Cephei-variables-HR-diagram-768x577.webp 768w\" sizes=\"auto, (max-width: 1280px) 100vw, 1280px\" \/><p id=\"caption-attachment-9056\" class=\"wp-caption-text\">A Hertzsprung\u2013Russell diagram, showing the luminosities and surface temperatures at which many classes of pulsating stars are found. Additional lines indicate where stars are found when they first fuse hydrogen into helium (zero-age main sequence, ZAMS), evolutionary tracks for stars of masses between 1 and 10 times that of the Sun, and the track along which a typical white dwarf of about 60% the Sun&#8217;s mass cools. Image credit: Wikimedia Commons\/Warrickball (<a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\">CC BY-SA 4.0<\/a>)<\/p><\/div>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"North_Star\"><\/span>North Star<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Beta Cephei is one of the stars in the far northern sky that take turns as the North Star over the course of Earth\u2019s 25,770-year precession cycle. Beta and Iota Cephei will be twin pole stars around the year 5200 AD, when they take over from the brighter <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (Gamma Cephei). <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> will replace <a href=\"https:\/\/www.star-facts.com\/polaris\/\">Polaris<\/a> (Alpha Ursae Minoris) after the year 3000 AD and appear the closest to the pole around 4200 AD.<\/p>\n<p>Alfirk and Iota Cephei will be replaced as pole stars by <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> (Alpha Cephei) around the year 7500 AD. The two stars will not be very accurate markers of true north. Each will come within 5 degrees of the pole. In comparison, <a href=\"https:\/\/www.star-facts.com\/polaris\/\">Polaris<\/a> comes within 0.5 degrees and is considerably brighter and easier to spot.<\/p>\n<p>Other stars that take turns as the North Star include <a href=\"https:\/\/www.star-facts.com\/deneb\/\">Deneb<\/a> and <a href=\"https:\/\/www.star-facts.com\/fawaris-delta-cygni\/\">Fawaris<\/a> in the constellation <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cygnus-constellation\/\">Cygnus<\/a>, <a href=\"https:\/\/www.star-facts.com\/vega\/\">Vega<\/a> in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/lyra-constellation\/\">Lyra<\/a>, Iota Herculis and Tau Herculis in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/hercules-constellation\/\">Hercules<\/a>, <a href=\"https:\/\/www.star-facts.com\/edasich-iota-draconis\/\">Edasich<\/a>, <a href=\"https:\/\/www.star-facts.com\/thuban\/\">Thuban<\/a> and Kappa Draconis in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/draco-constellation\/\">Draco<\/a>, and <a href=\"https:\/\/www.star-facts.com\/kochab\/\">Kochab<\/a> in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/ursa-minor-constellation\/\">Ursa Minor<\/a>.<\/p>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"Facts\"><\/span>Facts<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Shining at magnitude 3.23, Alfirk is, on average, the 216th brightest star in the night sky. It is usually slightly fainter than its <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a> neighbour <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (Gamma Cephei) and Delta Lupi in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/lupus-constellation\/\">Lupus<\/a>. It is about as bright as <a href=\"https:\/\/www.star-facts.com\/yed-posterior-epsilon-ophiuchi\/\">Yed Posterior<\/a> (Epsilon Ophiuchi) in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/ophiuchus-constellation\/\">Ophiuchus<\/a> and Eta Serpentis in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/serpens-constellation\/\">Serpens<\/a>, and it just outshines Alpha Pictoris in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/pictor-constellation\/\">Pictor<\/a>, Antinous (Theta Aquilae) in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/aquila-constellation\/\">Aquila<\/a>, Sigma Puppis in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/puppis-constellation\/\">Puppis<\/a>, Pi Hydrae in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/hydra-constellation\/\">Hydra<\/a>, and <a href=\"https:\/\/www.star-facts.com\/brachium-sigma-librae\/\">Brachium<\/a> (Sigma Librae) in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/libra-constellation\/\">Libra<\/a>.<\/p>\n<p>In traditional Chinese astronomy, Beta Cephei formed an asterism called \u4e0a\u885b (<em>Sh\u00e0ng W\u00e8i<\/em>), Left Wall First Imperial Guard. The asterism was part of the Purple Forbidden Enclosure, which contained constellations near the north celestial pole.<\/p>\n<p>The variation in the radial velocity of Beta Cephei was discovered by American astronomer Edwin Brant Frost in 1902. Frost initially assumed that the star was a spectroscopic binary and that the radial velocity radiations were caused by the star\u2019s orbital motion. By 1906, he found a period of 0.19 days.<\/p>\n<p><a href=\"https:\/\/www.star-facts.com\/alniyat-sigma-scorpii\/\">Alniyat<\/a> and <a href=\"https:\/\/www.star-facts.com\/mirzam\/\">Mirzam<\/a> were discovered to be variables of the same type several years later. The variable radial velocity of <a href=\"https:\/\/www.star-facts.com\/alniyat-sigma-scorpii\/\">Alniyat<\/a> was first reported by the American astronomer Vesto Slipher in 1904.<\/p>\n<p>The brightness variations of Beta Cephei were first detected by the German astronomer Paul Guthnick in 1913. The light variability had the same period as that determined by Frost.<\/p>\n<p>The variations of Beta Cephei stars were linked with pulsations by R. D. Levee and Otto Struve in 1952 and 1955. Based on spectroscopic studies of <a href=\"https:\/\/www.star-facts.com\/alniyat-sigma-scorpii\/\">Alniyat<\/a>, both astronomers concluded that the variability was intrinsic to the star and attributed the dominant period to stellar pulsations.<\/p>\n<p>Polish astronomer Wojciech Dziembowski studied the pulsations of \u03b2 Cephei stars with a focus on the excitation mechanism throughout his career. In the early 1990s, he concluded that these stars lay in the region of the Hertzsprung-Russell diagram where their oscillations could be driven by the kappa mechanism.<\/p>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"Name\"><\/span>Name<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The name Alfirk (pronunciation: \/\u02c8\u00e6lf\u0259rk\/) is derived from the Arabic <em>al-firqah<\/em> or <em>al-firq<\/em>, meaning \u201cthe flock (of sheep).\u201d It was historically also spelled Alphirk. It comes from the name <em>Al Kaw\u0101kib al Fir<\/em><em>\u1e33<\/em>, \u201cthe stars of the flock,\u201d which originally referred to Beta Cephei, <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> (Alpha Cephei), and Eta Cephei. <em>Kaukaba al-firq<\/em> was used for <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> and Alfirk and <em>kawakib al-firq<\/em> for Alpha, Beta and Eta Cephei. The name <em>Al Kaw\u0101kib al Fir<\/em><em>\u1e33<\/em> appeared in Timurid astronomer Ulugh Beg\u2019s star catalogue <em>Zij-i Sultani<\/em> of 1438-1439.<\/p>\n<p>The International Astronomical Union\u2019s (IAU) Working Group on Star Names (WGSN) approved the name Alfirk for Beta Cephei Aa on August 21, 2016. The name formally applies only to the primary component but has historically been used for the whole star system.<\/p>\n<p>Alfirk was given the Bayer designation Beta Cephei by the German astronomer Johann Bayer in his star atlas <em>Uranometria<\/em> of 1603. Bayer described the star as being \u201cunder the belt at the edge of the side\u201d (\u201c<em>sub cingulo ad finiftrum latus\u201d<\/em>). To the unaided eye, Beta Cephei appears just as bright as <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (Gamma Cephei), the second brightest star in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a>. It periodically outshines <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (mag. 3.21) during its pulsation cycle. <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> (Alpha Cephei), the constellation\u2019s brightest star, is visibly brighter at magnitude 2.46.<\/p>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"Location\"><\/span>Location<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Beta Cephei appears in the far northern sky and is part of the stick house asterism that dominates the <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">constellation Cepheus<\/a>. <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a>, the brightest star in Cepheus, lies on the imaginary line extended from <a href=\"https:\/\/www.star-facts.com\/schedar\/\">Schedar<\/a> through <a href=\"https:\/\/www.star-facts.com\/caph\/\">Caph<\/a> in <a href=\"https:\/\/www.constellation-guide.com\/cassiopeias-w\/\">Cassiopeia\u2019s W<\/a>. It forms the base of the house asterism with the supergiant Zeta Cephei. Alfirk appears at the base of the roof, between <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> and <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a>.<\/p>\n<p>At declination 70\u00b0 34\u2032, Alfirk is best seen from the northern hemisphere. It never rises above the horizon for observers south of the latitude 19\u00b0 S. The star is circumpolar throughout Europe, northern Asia, and North America.<\/p>\n<div id=\"attachment_9057\" style=\"width: 710px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-9057\" class=\"size-full wp-image-9057\" src=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Alfirk-location.webp\" alt=\"how to find alfirk,beta cephei location,where is alfirk in the sky\" width=\"700\" height=\"527\" srcset=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Alfirk-location.webp 700w, https:\/\/www.star-facts.com\/wp-content\/uploads\/2025\/10\/Alfirk-location-300x226.webp 300w\" sizes=\"auto, (max-width: 700px) 100vw, 700px\" \/><p id=\"caption-attachment-9057\" class=\"wp-caption-text\">Location of Alfirk (Beta Cephei), image: Stellarium<\/p><\/div>\n<h2 style=\"text-align: center;\"><span class=\"ez-toc-section\" id=\"Constellation\"><\/span>Constellation<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Alfirk is located in the constellation of <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a> (the King). Cepheus is one of the northernmost constellations in the sky. From the northern hemisphere, it can be seen circling <a href=\"https:\/\/www.star-facts.com\/polaris\/\">Polaris<\/a> throughout the year. Like the nearby <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cassiopeia-constellation\/\">Cassiopeia<\/a>, <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/draco-constellation\/\">Draco<\/a>, <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/ursa-minor-constellation\/\">Ursa Minor<\/a> and <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/camelopardalis-constellation\/\">Camelopardalis<\/a>, it was one of ancient <a href=\"https:\/\/www.constellation-guide.com\/constellation-names\/greek-constellations\/\">Greek constellations<\/a> catalogued by the Greco-Roman astronomer Claudius Ptolemy in his <em>Almagest<\/em> in the 2nd century CE. In Greek mythology, the constellation is associated with King Cepheus of Aethiopia, father of Andromeda and husband of Cassiopeia.<\/p>\n<p>Cepheus is the 27th largest constellation in the sky, occupying an area of 588 square degrees of the sky in the region of the northern celestial pole. Its brightest star, the fast-spinning <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> (Alpha Cephei), shines at magnitude 2.46 from a distance of 49.05 light-years. It is the only star in the constellation brighter than magnitude 3.0.<\/p>\n<p>Other relatively bright stars in Cepheus include the red giant <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (Gamma Cephei), the K-type supergiant Zeta Cephei, the orange subgiant Eta Cephei, the orange giant Iota Cephei, the Cepheid variable prototype Delta Cephei, the white giant star Theta Cephei, the F-type star Epsilon Cephei, and the variable red supergiant <a href=\"https:\/\/www.star-facts.com\/mu-cephei\/\">Mu Cephei<\/a> (Garnet Star).<\/p>\n<p><a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a> is also home to the blue-white supergiant Nu Cephei, the Mira variables T Cephei and S Cephei, the blue supergiant Lambda Cephei, the red supergiants <a href=\"https:\/\/www.star-facts.com\/vv-cephei\/\">VV Cephei A<\/a>, MY Cephei, W Cephei, V419 Cephei, ST Cephei and V354 Cephei, the orange hypergiant RW Cephei, and the binary red dwarf system Kruger 60, one of the closest star systems to the Sun.<\/p>\n<p>Many of the red supergiants in Cepheus are among the <a href=\"https:\/\/www.star-facts.com\/largest-stars\/\">largest stars known<\/a>. <a href=\"https:\/\/www.star-facts.com\/mu-cephei\/\">Mu Cephei<\/a> and ST Cephei both have estimated radii over 1,200 times that of the Sun.<\/p>\n<div id=\"attachment_4459\" style=\"width: 560px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-4459\" class=\"wp-image-4459 size-full\" src=\"https:\/\/www.star-facts.com\/wp-content\/uploads\/2019\/10\/Cepheus-constellation-map.webp\" alt=\"Cepheus constellation,cepheus stars,cepheus star map\" width=\"550\" height=\"641\" \/><p id=\"caption-attachment-4459\" class=\"wp-caption-text\">Cepheus constellation map by IAU and Sky&amp;Telescope magazine (Roger Sinnott &amp; Rick Fienberg) (<a href=\"https:\/\/creativecommons.org\/licenses\/by\/3.0\/https:\/\/creativecommons.org\/licenses\/by\/3.0\/\">CC BY 3.0<\/a>)<\/p><\/div>\n<p>Deep sky objects in Cepheus include the open cluster <a href=\"https:\/\/www.constellation-guide.com\/polarissima-cluster-ngc-188\/\">NGC 188<\/a> (the Polarissima Cluster), the <a href=\"https:\/\/www.constellation-guide.com\/wizard-nebula\/\">Wizard Nebula<\/a> (NGC 7380), the dark <a href=\"https:\/\/www.constellation-guide.com\/seahorse-nebula-barnard-150\/\">Seahorse Nebula<\/a> (B150), the <a href=\"https:\/\/www.constellation-guide.com\/shark-nebula-ldn-1235\/\">Shark Nebula<\/a> (LDN 1235), the <a href=\"https:\/\/www.constellation-guide.com\/ghost-nebula\/\">Ghost Nebula<\/a> (Sh2-136), the <a href=\"https:\/\/www.constellation-guide.com\/bow-tie-nebula-ngc-40\/\">Bow-Tie Nebula<\/a> (NGC 40), the <a href=\"https:\/\/www.constellation-guide.com\/question-mark-nebula-ngc-7822\/\">Question Mark Nebula<\/a> (NGC 7822), the <a href=\"https:\/\/www.constellation-guide.com\/rosebud-nebula-ngc-7129\/\">Rosebud Nebula<\/a> (NGC 7129), the <a href=\"https:\/\/www.constellation-guide.com\/valentine-rose-nebula\/\">Valentine Rose Nebula<\/a> (Sh2-174), the <a href=\"https:\/\/www.constellation-guide.com\/cave-nebula-caldwell-9\/\">Cave Nebula<\/a> (Sh2-155), the <a href=\"https:\/\/www.constellation-guide.com\/flying-bat-and-giant-squid-nebulae\/\">Flying Bat Nebula<\/a> (Sh2-129), the <a href=\"https:\/\/www.constellation-guide.com\/lion-nebula-sh2-132\/\">Lion Nebula<\/a> (Sh2-132), and the <a href=\"https:\/\/www.constellation-guide.com\/fireworks-galaxy-ngc-6946\/\">Fireworks Galaxy<\/a> (NGC 6946).<\/p>\n<p>The best time of the year to see the stars and deep sky objects in Cepheus is during the month of November, when the constellation appears higher above the horizon in the early evening. The entire constellation can be seen from locations north of the latitude 10\u00b0 S.<\/p>\n<p>The 10 brightest stars in <a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a> are <a href=\"https:\/\/www.star-facts.com\/alderamin\/\">Alderamin<\/a> (Alpha Cep, mag. 2.5141), <a href=\"https:\/\/www.star-facts.com\/errai-gamma-cephei\/\">Errai<\/a> (Gamma Cep, mag. 3.21), Alfirk (Beta Cep, mag. 3.23), Zeta Cephei (mag. 3.35), Eta Cephei (mag. 3.426), Iota Cephei (mag. 3.507), Delta Cephei A (mag. 4.07), Epsilon Cephei (mag. 4.18), Theta Cephei (mag. 4.22), and <a href=\"https:\/\/www.star-facts.com\/mu-cephei\/\">Garnet Star<\/a> (Mu Cep, mag. 4.23).<\/p>\n<p><strong><u>Alfirk \u2013 Beta Cephei<\/u><\/strong><\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"310\">Spectral class<\/td>\n<td width=\"310\">B1 IV<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Variable type<\/td>\n<td width=\"310\">Beta Cephei (Beta Canis Majoris)<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">U-B colour index<\/td>\n<td width=\"310\">-0.95<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">B-V colour index<\/td>\n<td width=\"310\">-0.22<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Apparent magnitude<\/td>\n<td width=\"310\">3.16 \u2013 3.27<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Absolute magnitude<\/td>\n<td width=\"310\">-3.03<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Distance<\/td>\n<td width=\"310\">690 \u00b1 40 light-years (210 \u00b1 10 parsecs)<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Parallax<\/td>\n<td width=\"310\">4.76 \u00b1 0.30 mas<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Radial velocity<\/td>\n<td width=\"310\">-8.2 \u00b1 2 km\/s<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Proper motion<\/td>\n<td width=\"310\">RA: +12.54 \u00b1 0.37 mas\/yr<\/td>\n<\/tr>\n<tr>\n<td width=\"310\"><\/td>\n<td width=\"310\">Dec.: +8.39 \u00b1 0.27 mas\/yr<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Constellation<\/td>\n<td width=\"310\"><a href=\"https:\/\/www.constellation-guide.com\/constellation-list\/cepheus-constellation\/\">Cepheus<\/a><\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Right ascension<\/td>\n<td width=\"310\">21<sup>h<\/sup> 28<sup>m<\/sup> 39.5968513<sup>s<\/sup><\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Declination<\/td>\n<td width=\"310\">+70\u00b0 33\u2032 38.574681\u2033<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Names and designations<\/td>\n<td width=\"310\">Alfirk, Beta Cephei, Beta Cep, \u03b2 Cephei, \u03b2 Cep, 8 Cephei, 8 Cep, HD 205021, HR 8238, HIP 106032, SAO 10057, FK5 809, BD+69\u00b01173, AG+70\u00b0738, AAVSO 2127+70, ALS 14839, GC 30118, GCRV 13520, PPM 10863, WEB 19222, PLX 5192.00, SKY# 40953, GSC 04465-02643, GEN# +1.00205021A, CSI+69 1173 1, AKARI-IRC-V1 J2128395+703338, SBC7 859, SBC9 1310, ROT 3532, PMSC 21274+7007AP, HGAM 1007, JP11 3361, PMC 90-93 568, UBV 21582, EUVE J2128+70.5, N30 4748, LAB 6, TD1 28199, TIC 321818578, MCW 989, 2XMM J212839.3+703338, 2E 4480, 2E 2128.0+7020, [HFE83] 1440, IRAS 21280+7020, 2MASS J21283958+7033389, TYC 4465-2643-1, Gaia DR2 2272185759992826624, Gaia DR3 2272185759996420992, STF 2806A, ADS 15032 A, CCDM J21287+7034A, IDS 21274+7007 A, WDS J21287+7034, WDS J21287+7034A, WDS J21287+7034Aa,Ab<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong><u>Beta Cephei Aa<\/u><\/strong><\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"310\">Mass<\/td>\n<td width=\"310\">7.4 M<sub>\u2609<\/sub><\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Luminosity<\/td>\n<td width=\"310\">20,000 L<sub>\u2609<\/sub> (15,900 \u2013 25,200 L<sub>\u2609<\/sub>)<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Radius<\/td>\n<td width=\"310\">7.22 \u00b1 0.42 R<sub>\u2609<\/sub><\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Temperature<\/td>\n<td width=\"310\">23,600 \u00b1 1,000 K<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Metallicity<\/td>\n<td width=\"310\">-0.23 dex<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Age<\/td>\n<td width=\"310\">8.7 km\/s<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Rotational velocity<\/td>\n<td width=\"310\">28 km\/s<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Surface gravity<\/td>\n<td width=\"310\">4.12 \u00b1 0.07 cgs<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong><u>Beta Cephei Ab<\/u><\/strong><\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"310\">Spectral type<\/td>\n<td width=\"310\">B6 V<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Mass<\/td>\n<td width=\"310\">5.0 M<sub>\u2609<\/sub><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong><u>Beta Cephei B<\/u><\/strong><\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"310\">Spectral type<\/td>\n<td width=\"310\">A2 V<\/td>\n<\/tr>\n<tr>\n<td width=\"310\">Apparent magnitude<\/td>\n<td width=\"310\">7.8<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"excerpt":{"rendered":"<p>Alfirk, Beta Cephei (\u03b2 Cep), is a triple star system located approximately 690 light-years away in the northern constellation Cepheus. With an apparent magnitude of 3.23, it is the third brightest point of light in Cepheus, after Alderamin (Alpha Cephei) and Errai (Gamma Cephei). The primary component in the system serves as the prototype for&hellip;&nbsp;<a href=\"https:\/\/www.star-facts.com\/alfirk-beta-cephei\/\" class=\"\" rel=\"bookmark\">Read More &raquo;<span class=\"screen-reader-text\">Alfirk (Beta Cephei)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":9055,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"off","neve_meta_content_width":70,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":"","footnotes":""},"categories":[79,737,78,160],"tags":[215,749,565,806,981,1231,1073,288,320,1995,2215,2216,164,323,1230,711,315,750,192,437,319,321,325,90,309,208,287,300,172,80,2218,193,322,2217,1338,317,161,1243,2219],"class_list":["post-9044","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-beta-cephei-variables","category-cepheus-stars","category-multiple-star-systems","category-north-pole-stars","tag-alderamin","tag-alfirk","tag-algenib","tag-alniyat","tag-alpha-lupi","tag-alpha-muscae","tag-alpha-pictoris","tag-beta-canis-majoris","tag-beta-cephei","tag-brachium","tag-delta-cephei","tag-delta-lupi","tag-deneb","tag-edasich","tag-epsilon-centauri","tag-epsilon-persei","tag-errai","tag-eta-cephei","tag-hadar","tag-imai","tag-iota-cephei","tag-iota-herculis","tag-kappa-draconis","tag-kappa-scorpii","tag-kochab","tag-mimosa","tag-mirzam","tag-north-star","tag-polaris","tag-shaula","tag-sigma-puppis","tag-spica","tag-tau-herculis","tag-theta-aquilae","tag-theta-ophiuchi","tag-thuban","tag-vega","tag-yed-posterior","tag-zeta-cephei"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/posts\/9044","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/comments?post=9044"}],"version-history":[{"count":9,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/posts\/9044\/revisions"}],"predecessor-version":[{"id":9396,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/posts\/9044\/revisions\/9396"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/media\/9055"}],"wp:attachment":[{"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/media?parent=9044"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/categories?post=9044"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.star-facts.com\/wp-json\/wp\/v2\/tags?post=9044"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}