Twilight Phenomena

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An example of Twilight phenomenon, as seen from the LA-24 Long Range Tracking Telescope site on Tranquillon Peak in northern Santa Barbara county, lights up the night sky over Vandenberg AFB following the launch of an unarmed Minuteman III missile Sept. 19, 2002 (Official USAF Photo by Dennis Fisher, 30th Communications Squadron, Vandenberg AFB, CA)

Twilight phenomenon is produced when unburned particles of missile or rocket propellant and water left in the vapor trail of a launch vehicle condenses, freezes and then expands in the less dense upper atmosphere. The exhaust plume, which is suspended against a dark sky is then illuminated by reflective high altitude sunlight, which produces a spectacular, colorful effect when seen at ground level.

The phenomenon typically occurs with launches that take place either 30 to 60 minutes before sunrise or after sunset when a booster rocket or missile rises out of the darkness and into a sunlit area, relative to an observer's perspective on the ground.

This phenomenon usually produces a cloud of green, blue, white and rose colored hues which takes on a corkscrew appearance as it is whipped around by wind currents. It is seen within two to three minutes after a launch has occurred. Depending on weather conditions, it could remain in the sky for up to half an hour before dispersing.

Pre-dawn launches are probably less spectacular than their dusk counterparts. During dusk launches, the sunlight shines through the exhaust plume. Pre-dawn launches, on the other hand, produce a more subtle display because the sunlight directly reflects off of the plume.

At Vandenberg AFB in California, more than 1,800 missiles and space boosters have been launched from the central California coastline in northern Santa Barbara County since December 1958. However, only a small percentage of these launches have created the twilight phenomenon.

Some observers have assumed -- incorrectly -- that the missile creating the aerial spectacle must have malfunctioned and/or been destroyed while in flight. That belief stems from the appearance of the missile's contrail as it becomes twisted into giant pretzel shapes by upper altitude air currents or wind shear.

No malfunctioning missile has ever created the phenomenon. On the rare occasions when a missile does malfunction, it is destroyed by a Range Safety Officer before reaching an altitude high enough in the atmosphere where the twilight phenomenon occurs.

The phenomenon's appearance and intensity varies with viewer location, but can usually be seen throughout the state of California, and as far away as Arizona, Nevada and Utah. On the East Coast, similar sightings can be observed during twilight launches of the space shuttle and other expendable launch vehicles from NASA's Kennedy Space Center and the U.S. Air Force's launch complexes at Cape Canaveral in Florida.