Conductor Osmo Vänskä brings music of four countries to his concert with the NSO, beginning with the Helios Overture by Denmark’s best-known composer, Carl Nielsen, in which the composer traces the course of the sun across the sky from dawn to twilight. From Hungary’s best-known composer, Béla Bartók, we hear his final composition, a somber, deeply-felt concerto for an instrument that rarely gets to enjoy the spotlight, the viola. Elegy, composed in 1980 by Taiwanese composer Tsung-Hsien Yang, also features the somber, veiled tone of the solo viola to carry its message of grief. To conclude his eclectic program, Vänskä offers from his native Finland Sibelius’ mighty Fifth Symphony, with its life-affirming spirit and resounding, heroic ending.