Editing Bayer designation (section)

== Order by magnitude class ==

In most constellations, Bayer assigned Greek and Latin letters to stars within a constellation in rough order of [[apparent magnitude|apparent brightness]], from brightest to dimmest.  The order is not necessarily a precise labeling from brightest to dimmest: in Bayer's day stellar brightness could not be measured precisely. Instead, stars were traditionally assigned to one of six magnitude classes (the brightest to first magnitude, the dimmest to sixth), and Bayer typically ordered stars within a constellation by class: all the first-magnitude stars (in some order), followed by all the second-magnitude stars, and so on. Within each magnitude class, Bayer made no attempt to arrange stars by relative brightness.<ref name=jha17_50_189>{{cite journal | title=A Star Catalogue Used by Johannes Bayer | last=Swerdlow | first=N. M. | journal=Journal for the History of Astronomy | volume=17 | issue=50 | pages=189–197 |date=August 1986 | bibcode=1986JHA....17..189S | doi=10.1177/002182868601700304 | s2cid=118829690 }} See p. 192.</ref> As a result, the brightest star in each class did not always get listed first in Bayer's order—and the brightest star overall did not necessarily get the designation "Alpha".  A good example is the constellation [[List of stars in Gemini|Gemini]], where [[Pollux (star)|Pollux]] is Beta Geminorum and the slightly dimmer [[Castor (star)|Castor]] is Alpha Geminorum.

In addition, Bayer did not always follow the magnitude class rule; he sometimes assigned letters to stars according to their location within a constellation, or the order of their rising, or to historical or mythological details. Occasionally the order looks quite arbitrary.<ref name="Ridpath"/>

Of the 88 modern constellations, there are at least 30 in which Alpha is not the brightest star, and four of those lack a star labeled "Alpha" altogether. The constellations with no Alpha-designated star include [[Vela (constellation)|Vela]] and [[Puppis]]—both formerly part of [[Argo Navis]], whose Greek-letter stars were split among three constellations. [[Canopus]], the former α Argus, is now α Carinae in the modern constellation [[Carina (constellation)|Carina]]. [[Norma (constellation)|Norma's]] Alpha and Beta were reassigned to [[Scorpius]] and re-designated [[N Scorpii|N]] and [[H Scorpii]] respectively, leaving Norma with no Alpha. [[Francis Baily]] died before designating an Alpha in [[Leo Minor]], so it also has no Alpha. (The star [[46 Leonis Minoris]] would have been the obvious candidate.)