As it has for centuries, the morning sun on the Summer Solstice casts a shadow upon this large petroglyph spiral at Petrified Forest National Park. Beginning a few minutes after sunrise on the longest day of the year, the rays from the climbing sun gradually illuminate the panel, causing the shadow line to cross the boulder face from left to right. Within half an hour, the shadow neatly bisects the glyph. This interplay of light, shadow and prehistoric art only occurs for a couple of days on either side of the solstice. There are a number of solar-interactive calendar markers at Petrified Forest, with the best known located at the Puerco Pueblo ruin in the middle of the park. The Puerco “Sun Dagger” display is visible there for a week on either side of the June 21 solstice. Rangers will conduct programs daily through June 28 during the mid-morning interaction, which is easily accessible from the path at the south end of the site. June 14-28 there will be summer solstice marker viewings each morning.