It’s no accident that Donegal-based quintet Altan has reached the top of Ireland’s crowded folk heap. The group’s elegant arrangements of centuries-old ballads, jigs, reels, and airs are centered around the haunting Gaelic vocals (similar in style to Clannad’s Maire Brennan, also a Donegal native) and smooth fiddling of Mairéad Ni Mhaonaigh. Another unique aspect of Altan’s sound is the twin fiddle power revealed when Ni Mhaonaigh and Ciarán Tourish team up to lead the group through rollicking dance tunes. Altan’s newest addition, accordionist Dermot Byrne, adds additional instrumental color, while bouzouki player Ciarán Curran and guitarist Dáithí Sproule provide the rhythmic drive that holds it all together. At 7 p.m. at the Museum of Natural History’s Baird Auditorium, 10th & Constitution Ave. NW. $20. (202) 357-3030. (Ken Roseman)