B
back-staff: an old instrument for measuring the altitude of the Sun while facing away from it. The Davis quadrant, designed by the English captain John Davis, is actually a form of back-staff.
(or bay en imy wenut): literally a “palm rib of the observer of the hours”. It was an ancient Egyptian instrument or sighting device, used in conjunction with a merkhet to observe and time transits.
Beltane {Beltaine}: an ancient Celtic festival held on the 1st of May, when bonfires were lit. It is one of the
cross-quarter days
bissextile
A leap-year (from bis sextus dies, or doubled 24 February).
blue moon
There are at least two possible meanings. It can mean a second full moon in a given calendar month. It seems that this “meaning” was accidentally invented by Sky and Telescope magazine in 1946, but it has passed into wide usage. Alternatively, it may mean that the Moon actually has a blue coloration, due to smoke or other aerosols in the atmosphere. Both phenomena are rare (the second more so), hence the expression “once in a blue moon”.
brachiolus
From the Latin for “little arm” it is a movable arm which acts as a suspension point for a cord on a card dial.
break of day: see daybreak.
British Summer Time [BST]
See time (types of).