The Northern Lights are caused by particles coming from the Sun. As the particles enter the upper reaches of the atmosphere they strike other atoms such as Oxygen and Nitrogen. When the collisions occur, a photon of light is released and you see a glow. The color of the light depends on which atoms are hit and the height where the collisions occur. Oxygen atoms give off red and green light while Nitrogen atoms give off blue and violet light.
Red aurora indicates the most intense activity.
You probably saw a rather uniform red glow in the sky. In the Northern regions, especially Alaska, the aurora looks like very distinct, massive flowing sheets that reach from horizon to horizon. One ripple can move across the sky in less than a couple of seconds. These flashes look like light flowing from the horizon to the sky. Aurora occur throughout the year but are best observed during the winter months when the nights are longer and the North pole is tilted away from the Sun.