Last Thursday, sky watchers throughout the Middle East saw an unnerving sight – a swirling spiral of light in the sky. Reports to police of the unidentified flying object were quickly followed by videos posted on YouTube. Admittedly, the videos are pretty; spirals of light aren't something we see everyday. But, it's also not the UFO conspiracy theorists would love to find. The sighting has been confirmed as a regular ol' missile launch.According to The Voice of Russia, the country's Strategic Missile Forces conducted a successful test of the "Topol" Intercontinental Ballistic Missile Thursday. The missile launched from the firing ground at “Kapustin Yar” in Astrakhan in Southern Russia and reportedly successfully hit its target on the firing range “Sary-Shagan” in Kazakhstan.But Israel's Ynet News has reported a different result. Chairman of the Israeli Astronomical Association Dr. Yigal Pat-El suggested that the test failed and that’s what caused the spiral Middle Easterners saw. “It most likely spun out of control and its remnants and the fuel was what people saw. It reached a height of 200-300 kilometers and that’s why it was seen from so many locations,” he told Ynet.So how do these things come together to explain the light spiral? It's all a matter of perspective. The missile's path from launch site to target would have brought it into visual range of countries the Middle East. The spiral is little more than the apparent motion of the booster as seen from the viewers' perspective.In flight, any rocket will roll around its longitudinal axis, the line from nose to tail. The rolling motion can be caused by the rocket's fins. Hinged at the rear, fins add lift, but if they're all hinged at the same angle they also produce a roll rolling motion. Some early rockets used, and some modern rockets still use, this method to generate stable flight. If a rocket malfunctions or starts leaking fuel from one side of its body or nozzle, it will take on the same roll motion.Seen from the ground, the exhaust from a rolling rocket would look like a spiral.It's an illusion, like what you see from one of those rotating sprinklers. A sprinkler shoots water out from one point but rotates at the same time. If you're watching it from the right angle, it looks like the water is forming a spiral. It nifty, but an illusion of motion.Last week's sighting in the Middle East wasn't the first of its kind and it's unlikely to be the last. In 2009, skywatchers in Norway were treated to a similarly unnerving sight when twin spirals were seen in the night sky. Both were rooted in a Russian rocket test that failed. In 2010, one of SpaceX’s Falcon 9 rockets gave residents of Australia the same neat show.Sorry, UFO hunters. Those spirals of light in the sky are just a neat, if slightly creepy looking, little bit of rocket science.
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