One spectacular ephemeral feature that can be seen from Fallbrook are the missile launches themselves and their vapor trails from Vandenberg Air Force Base, ~200 miles from Fallbrook! (192 miles from my house at an azimuth of 65.5o west of north, to be precise.) Hayne Palmour's stunning photo of the contrails produced by the 23 June 1997 Minuteman II missile launch (138 kB) shows a rare example of the "twilight phenomenon" in addition to beautiful contrails. (If you don't want to download the full picture, I have made a schematic representation that is only 8 kB.) See Analysis of 23 June 1997 Minuteman II Contrail for more information.
At least two types of rockets are launched from Vandenberg:
- Satellites launched into near-polar Earth orbits by rockets such as the Delta, and
- Missiles launched into very-low Earth orbits that end with impacts into islands in the South Pacific, such as a Minuteman II missile.
Many satellites are launched near times of dusk or dawn in order to position the satellite at the terminator between day and night. This gives us observers the great advantage of being able to see the firing of the engines and the separation of the rocket stages against a dark sky, followed by the contrails of the exhaust. The precession of near-polar orbits can keep the satellite at the terminator for long periods of time.
Contrary to what most people think, the contrails in general do not look like they were formed from a rocket! The upper-level winds, with typical speeds around 100 mph, quickly blow the contrails into corkscrews or spirals. It takes only 5 minutes for 100 mph winds to move a given spot on the contrail 5 miles away from the rocket's path. Since the contrails can persist for an hour, there is plenty of time for the wind to play with the contrail.
Further, wind direction, as well as speed, varies dramatically at different altitudes and locations. Watch weather satellite picture loops and you will often be able to see high clouds moving in different directions than the lower clouds. This change of wind direction with height causes the corkscrew shapes that always make observers think that the rocket has blown up, which it never has if you are seeing the contrail from Fallbrook! (Rockets are blown up at much lower altitudes than those which produce the contrails visible to us.)
Launches that occur when the sun is just below the horizon are especially spectacular:
- The lowest part of the contrail is almost never seen due to the "haze/smog" layer and possibly darkness.
- The next level up is usually red, because it is illuminated by sunshine that has gone through the maximum amount of the Earth's atmosphere, just like at sunset (since it is sunset for that part of the contrail).
- The upper part is usually white, illuminated by full sunshine.
- Above that, the contrail doesn't exist because the rocket is too high for the hot water vapor exhaust to produce condensation clouds (the "con" in "contrail") or too far from the observer to see.
Finally, once in a great while ("a small number out of more than 1,700 missiles" according to Vandenberg Air Force Base), an extra added bonus of a "twilight phenomenon" occurs. This spectacular event features the colors of the rainbow (specifically, green, blue, white and rose-colors) emanating from the top of the contrail. It is created when unburned missile propellant and water freezes in the upper atmosphere, and those frozen crystals are illuminated at the right angle by the sun, which must be below the horizon by 30-60 minutes of time.
MSLS LAUNCH SUCCESSFUL January 16, 1997 Release Number 97-0107 - NEWS RELEASE Vandenberg Air Force Base (if it still on-line) has a bit more about the twilight phenomenon. The Minuteman II missile launch of 23 June 1997 was the last spectacular contrail with twilight phenomenon that I know of. See Hayne Palmour's beautiful picture from the NCT 6/24/97, B1.
Satellite launches are often announced in advance, so if you really really want to see one, see Brian Webb's Vandenberg launch schedule, and then check the Vandenberg Launch Update Line at 805-606-1857 as the launch nears.
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Copyright © 1997-2003 by Tom Chester.
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Last update: 9 February 2003.