After Sunday's post on Yosemite's waterfalls I received a few emails about the "Firefall" on Horsetail Falls. The questions all centered around "is this real" and "what causes this effect". The Firefall is a result of two things. First, the sun has to be low in the horizon so that light traveling through the extra thickness of the atmosphere loses it's blue spectrum and becomes yellow (this is why sunsets are yellow/gold). Next, the sun needs to be at around 257 degrees and near the horizon to create the correct angle to light the side of El Capitan underneath Horsetail Fall. This often happens at sunset in the last two weeks of February.
When these conditions do collide, the light creeps across the falls over about a 15 minute period. Initially the entire face is lit, and then, for around a minute, only the fall glows. This set of images is the sequence from when the entire light hit the face until the light is finally gone. In this case, the face is actually lit by the moon (or, more properly, the sun bouncing off the moon). All the same principles apply - just think of this as a very very cool "bank shot".
Here is the image from the sequence that I like the most. Only the falls and a little of the rock face are lit so it looks like the water is glowing.