What is Anomers?

In a Haworth projection the ring of a cyclic sugar is drawn flat, perpendicular to the page, with its oxygen at the back right and its substituents above or below the ring. The hemiacetal carbon (C1 of an aldose) is the anomeric carbon; the two configurations it can take give two diastereoisomers, the anomers: for a D sugar, $\alpha$ has the anomeric $\ce{OH}$ below the ring (opposite the $\ce{CH2OH}$), $\beta$ above. In water the anomers interconvert through the open chain, and the optical rotation of a freshly dissolved anomer drifts to an equilibrium value: mutarotation.