(Reuters) - Wall Street's main indexes opened flat to slightly higher in Tuesday's shortened trading session, with U.S. stocks entering a historically strong period before rounding off their second consecutive year of gains.

The Dow Jones Industrial Average rose 9.5 points, or 0.02%, at the open to 42,916.48. The S&P 500 rose 10.6 points, or 0.18%, at the open to 5,984.63​, while the Nasdaq Composite rose 53.6 points, or 0.27%, to 19,818.476 at the opening bell.