Watch Out for Solar Sail Flares   
       
   February 1, 2011: It's a calm and peaceful night. Stars twinkle in the velvety   
   darkness overhead as a distant plane blinks silently on the horizon. You could   
   almost hear a pin drop.   
   [...]   
   A camera in Finland caught NanoSail-D flaring on Jan. 30th. The streak of   
   light was almost three times brighter than a 1st-magnitude star. Credit: Esko   
   Lyytinen. [details] That is, until the flare.   
       
   High overhead, out of the darkness, a bright light surges into view. For 5 to   
   10 seconds it outshines the brightest stars in the sky, mimicking a supernova,   
   perhaps even casting faint shadows at your feet. The silence is broken by your   
   own excited shouts.   
       
   Could this happen to you?   
       
   "It could, if you happen to be outside when NanoSail-D flies by," says Dean   
   Alhorn of the Marshall Space Flight Center in Huntsville, AL. "We think the   
   spacecraft could produce this kind of display from time to time when sunlight   
   glints off the reflective fabric of its solar sail."   
       
   On Jan. 21st, NanoSail-D unfurled a 10 m2 sail 650 km above Earth's surface,   
   becoming the first solar sail to orbit our planet. For the next few months it   
   will skim the top of the atmosphere, slowly descending in a test of 'drag   
   sails' as a means of de-orbiting space junk. If all goes as planned, the   
   spacecraft will disintegrate like a meteor in April or May of 2011, dispersing   
   harmlessly more than 1100 km high.   
       
   Meanwhile, sky watchers should be alert for flares.   
       
   Many people have already seen Iridium flares--brilliant flashes of sunlight   
   glinting off the flat antennas of Iridium communication satellites. Some   
   Iridium flares are so bright, they can be seen in broad daylight. NanoSail-D   
   could be even brighter.   
   [...]   
   The reason for Iridium flares. Credit: SeeSat-L. [more information]   
       
   "The surface area of our sail is six times greater than that of a single   
   Iridium antenna," points out Alhorn. "Plus, we're closer to Earth. It all adds   
   up to a much brighter flash."   
       
   As NanoSail-D gets closer to Earth, it could theoretically produce flashes of   
   light 10 to 100 times (2.5 to 5 astronomical magnitudes) brighter than the   
   planet Venus. That's the sort of thing you can see even through city lights.   
       
   In between flares, however, the sail is fairly dim. Internationally-recognized   
   satellite tracking expert Ted Molczan describes what he and others have been   
   seeing:   
       
   "NanoSail-D can be a challenging object to spot, but by no means impossible.   
   At its faintest, it has been invisible even in large binoculars, but at its   
   brightest, it has been seen easily with the un-aided eye. The great variation   
   in brightness is due to its shape; it is a large, thin sheet of highly   
   reflective material. Seen edge-on, it is faint, but seen face-on at a   
   favorable sun-angle, it may rival the brightest stars."   
       
   NanoSail-D flyby predictions may be found in several places on the web:   
   Heavens-Above, Spaceweather.com, and Calsky among others. These sites will   
   tell you when the sail will soar overhead--but not when it will flare. The   
   orientation of the sail isn't known precisely enough for that.   
       
   "Because it is impossible to predict exactly when NanoSail-D will be bright,   
   observers can increase their chance of success by watching over a period of   
   least several minutes," says Molczan. "A plot of its predicted path on a star   
   chart, with annotations of the time at intervals of one minute or so, will   
   help the observer stay focused on the satellite's approximate position as it   
   moves across the sky. Observe with the unaided eye, or binoculars with a wide   
   field of view, like 7x50s."   
   [...]   
   A conjunction of the Moon and NanoSail-D over Buenos Aires, Argentina,   
   photographed by Enzo De Bernardini on Jan. 27th. On this occasion, the sail   
   was not visible to the unaided eye. De Bernardini used a 3-inch refracting   
   telescope to capture the 7th-magnitude streak. [more]   
       
   The brightest flares are likely to occur when the spacecraft is near the   
   horizon. Former NanoSail-D principal investigator Mark Whorton (previously at   
   NASA, now at Teledyne) explains why:   
       
   "Early in the mission NanoSail-D will be tumbling, so it really doesn't matter   
   where it is in the sky. Flashes might occur almost anywhere along its path.   
   But later in the mission it will be aerodynamically stabilized: the flat   
   surface of the sail will face forward, much like the sail on a terrestrial   
   sailing ship. That means you will see it edge on (dim) when it is directly   
   overhead and face on (bright) when it is closer to the horizon."   
       
   So check the predictions, go outside and take a look. Says Alhorn, "You might   
   see something worth shouting about."   
       
   BONUS: To encourage amateur astronomers to monitor the sail, NASA and   
   Spaceweather.com have joined forces to stage a photo contest. Cash prizes   
   ranging from $100 to $500 are being offered for best images of NanoSail-D   
   submitted between now and the time the sail disintegrates. High-resolution   
   telescopic images of the spacecraft, wide-angle shots of NanoSail-D soaring   
   overhead, and lucky-shots of flares are all eligible. Visit nanosail.org for   
   complete details.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   NanoSail-D -- home page   
       
   Solar Sail Stunner -- Science@NASA   
       
   NanoSail-D tracking sites:Heavens Above, Spaceweather.com, Calsky   
       
   NanoSail-D Photo Contest   
       
   A Brief History of Solar Sails -- Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.59   
    * Origin: NCS BBS (1:3828/7)