Shape Shifting St Kilda

Watch this strange visual effect from my friend and videographer Mo Thomson. He's been shooting video footage from the Isle of Harris and Lewis for a few years now, but managed to catch this strange optical effect when the sun set behind the island of St Kilda.

St Kilda - sunset silhouette from Mo Thomson on Vimeo.

The conclusion I have come to is that what we are seeing is a shadow of the island not the island itself, which then appears to change shape and angle as the sun moves in behind it. I am not certain, but it seems like the most viable idea I  can come up with.