Alpheratz Links Andromeda the Chained Princess With Pegasus the Winged Horse

Summary: Alpheratz links its current home constellation, Andromeda the Chained Princess, with its previous home constellation, Pegasus the Winged Horse.

Alpha Andromeda, known traditionally as Alpheratz: Stockholms Observatorium, Public Domain, via Wikimedia Commons

As a linking star, Alpheratz links its current home constellation, Andromeda the Chained Princess, with its previous home constellation, Pegasus the Winged Horse, and historically claims two Bayer designations, one for each constellation.

Prior to the 20th century, nebulous boundaries and star sharing characterized the constellations in their apparently westward parade across the celestial sphere, the imaginary sphere projected outward from Earth. Founded in 1919 as an international association, the International Astronomical Union (IAU) established 88 clearly named constellations in 1928 and precise constellation boundaries in 1930. The boundaries of the 88 constellations became official with ratification in 1933.

Prior to IAU’s official maps, Alpheratz provided double duty as a shared star for two constellations in the celestial northern hemisphere. Alpheratz marked both the face of the Chained Princess in constellation Andromeda and the navel of the Winged Horse in constellation Pegasus.

Celestial cartographer Johann Bayer (1572-March 7, 1625) assigned two designations to the second magnitude star in his system of stellar nomenclature. Recognizing Alpheratz’s shared status by both Andromeda the Chained Princess and Pegasus the Winged Horse constellations in the celestial northern hemisphere, Bayer designated Alpheratz as Alpha Andromedae (α Andromedae; Alpha And; α And) and also as Delta Pegasi (δ Pegasi; Delta Peg; δ Peg).

The International Astronomical Union’s standardization of boundaries eliminated fuzzy borders and star sharing. Official star maps created by the International Astronomical Union, in collaboration with Sky & Telescope magazine, have definitively removed Alpheratz from Pegasus the Winged Horse constellation. The 1933 ratification has officially settled Alpheratz in Andromeda the Chained Princess constellation.

Alpha Andromedae is now considered Alpheratz’s exclusive Bayer designation. Since 1930, Delta Pegasi has become an obsolete designation.

Yet Alpheratz maintains an association with Pegasus the Winged Horse constellation through continued participation in the Great Square of Pegasus asterism. As a particular region of the celestial sphere, a constellation comprises specific stars. As a recognizable pattern of stars in Earth’s night skies, an asterism comprises stars from one or more official constellations. Asterisms that rely upon two or more constellations for their pattern transcend official constellation boundaries.

As an asterism, the Great Square of Pegasus takes shape by pooling stars from two neighboring constellations. Pegasus the Winged Horse constellation provides three stars. Alpha Pegasi (α Pegasi; Alpha Peg; α Peg) marks the square’s southwestern corner. Beta Pegasis (β Pegasi; Beta Peg; β Peg) anchors the asterism’s northwestern corner. Gamma Pegasi (β Pegasi; Beta Peg; β Peg) marks the Great Square’s southeastern corner.

The four star Great Square of Pegasus asterism borrows Alpha Andromedae to complete its starry outline. Alpha Andromedae represents the asterism’s northeastern corner.

Alpha Andromedae also connects with its formerly shared constellation through its traditional name. Alpheratz derives from the Arabic word for horse (al-faras), appearing in the descriptive phrase, surrat al-faras (“navel of the horse”), applied in Arab astronomy to Alpha Andromedae.

Alpheratz is no longer a shared star that crosses constellation boundaries. Instead, Alpheratz is a linking star that completes an asterism by linking two constellations.

The takeaway for Alpheratz as a link between Andromeda the Chained Princess constellation and Pegasus the Winged Horse constellation is that the blue white binary star system officially now belongs to Andromeda but continues to associate with Pegasus by way of the multi-constellatory Great Square of Pegasus asterism.

Alpha Andromedae (lower left) marks the face of Andromeda the Chained Princess, near her left eye, in 1822 depiction in Scottish rhetorician Alexander Jamieson’s A Celestial Atlas, Plate III: Alexander Jamieson, Public Domain, via U.S. Naval Observatory Library

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Alpha Andromeda, known traditionally as Alpheratz: Stockholms Observatorium, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Alpheratz.gif

Alpha Andromedae marks the face of Andromeda the Chained Princess, near her left eye, in 1822 depiction in Scottish rhetorician Alexander Jamieson’s A Celestial Atlas, Plate III: Alexander Jamieson, Public Domain, via U.S. Naval Observatory Library @ http://aa.usno.navy.mil/library/

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