Santa and His Sled
December 24, 2007
Viewing the Sun in H-alpha, a deep red color (656.3 nm wavelength) produced by neutral hydrogen, reveals ribbons of relatively cool gas standing above the hotter chromosphere -- the Sun's middle atmosphere. Ribbons (also called filaments) snake around the boundaries between regions of opposite magnetic polarity in the photosphere (visible surface) below the chromosphere. But just what's that straight ribbon?
Look closer and you'll see that it's a rare passage of an eight-reindeer-power sled (making a pre-Christmas check ride) between the Sun and the U.S. Air Force's Optical Solar Patrol Network (OSPAN) telescope, stationed at the National Solar Observatory atop Sacramento Peak, New Mexico. OSPAN is a semi-autonomous, remotely commandable patrol telescope designed for studies of solar activity in support of space weather specifications and forecasts. OK, this transit is actually a jetliner/sled (with the help of a little photo editing) and was observed on December 14, 2004, at 23:42 UT (4:42 p.m. Mountain Standard Time). The jet appears to be a Boeing 737. With an average length of almost 40 m (130 ft.), the scale on this image puts this 737 about 177 km (110 mi) away. It's seen here departing the El Paso, Texas, airport. While such transits aren't uncommon in urban areas, only ten or so aircraft passages a year are expected at remote Sacramento Peak, and only a few coincide with OSPAN's once-a-minute, 50 ms exposures.
Thanks to the ISOON team, Air Force Research Laboratory, for this image.