A mansion is a night's travel. The system exists because the Moon covers roughly one twenty eighth of the circle between one nightfall and the next. Each mansion is exactly twelve degrees fifty one minutes wide, one twenty eighth of three hundred and sixty. Al Butain is the second of them, running from 12 degrees 51 minutes of Aries to 25 degrees 43 minutes of Aries. The Moon's mean daily motion of about thirteen degrees eleven minutes is slightly more than one mansion, so it completes the circuit of all twenty eight in the sidereal month of twenty seven and a third days, not in the twenty nine and a half of the synodic month the phases follow.
The Arabic manazil al qamar reached Latin Europe through translation in the twelfth and thirteenth centuries, and the magical use of the mansions travelled with the astronomical scheme rather than after it. Agrippa set out all twenty eight with their degrees and their operations in the second book of the Three Books of Occult Philosophy, and that chapter, not any Arabic original, is where almost every later English language list comes from. Al Butain is a transliteration, and the spellings vary widely between sources.
There is a problem in those degrees that the printed lists rarely flag. The mansions are named for star groups, but the boundaries above are measured in the tropical zodiac, anchored to the equinox, which drifts against the stars at about one degree every seventy two years. The Arabic scheme was fixed to the stars themselves. Something close to twenty degrees of precession has accumulated since the medieval transmission, so a mansion's tropical degrees no longer contain the stars it is named after. Both readings are in circulation and neither is a misprint.