Clouds visible on the eastern horizon were pink from the last bright colors of a spectacular sunset. The moon had risen about 30 minutes into the sky and was adding its meager light across the Upper Geyser Basin. Castle Geyser erupts about every 12 hours and eruptions last for about 50 minutes. Castle started to erupt after the pink light had faded from the cone but the large clouds to the west behind me cast a faint pink glow across the entire landscape. Water bursts went 60 feet into the air and helped push the clouds of steam hundreds of feet higher.