Buzz Aldrin, Apollo astronaut and second to walk on the moon, demonstrates the ALFMED device astronauts used to record the cosmic rays that flashed inside their eyeballs during their journeys to the moon and back. Credit: NASA
With the 45th anniversary of the Apollo 11 moon landing approaching this weekend, let’s look back at a peculiar discovery made while astronauts Buzz Aldrin and Neil Armstrong left the safety of Earth for the lunar unknown.
Earth’s atmosphere and magnetic field protects us from cosmic rays, which are high-speed protons and other atomic nuclei that shoot across the galaxy like so many submicroscopic billiard balls. They pack a punch. The most powerful contain the same energy as a baseball traveling at 56 mph. Scientists believe cosmic rays originate from exploding supernovae.
En route to the moon in 1969 Buzz Aldrin reported seeing flashes in his eyes in the darkened cabin of the command module. Neil Armstrong noticed them too. Back in 1952, physicist Cornelius Tobias predicted that cosmic rays could interact with light-sensing cells in astronauts’ eyeballs to generate the perception of flashing lights.
Flash patterns observed by Apollo astronauts.
After Aldrin and Armstrong reported their experience, NASA asked future astronauts to be on the lookout for the same and report anything unusual. Later missions even included a special device called the ALFMED (Apollo Light Flash Moving Emulsion Detector), a helmet the astronaut wore to dark-adapt the eyes to better see the flashes. It also held film that recorded cosmic ray hits that were later correlated with the times flashes were seen.
The device conclusively proved that the flashes, dashed lines and occasional glowing puffs the space travelers reported were clearly caused by cosmic rays.
While not every Apollo astronaut saw them, most did and described them as white or colorless spots, stripes, streaks, explosions and multiple tracks. They occurred on average once every 2.9 minutes. For some, the flashes were so frequent it made getting to sleep a challenge.
A cosmic ray hit on the sensor in a camera appears as a segmented line. Credit: NASA/Don Petit
You don’t have to go all the way to the moon to experience this ocular light show. Free from the protection of the atmosphere, International Space Station (ISS) astronaut Don Petit saw them from Earth orbit, describing the flashes poetically as ‘fairies’:
“In space I see things that are not there. Flashes in my eyes, like luminous dancing fairies, give a subtle display of light that is easy to overlook when I’m consumed by normal tasks. But in the dark confines of my sleep station, with the droopy eyelids of pending sleep, I see the flashing fairies.”
It’s thought that as a cosmic ray passes through the retina it causes rod and cone cells to fire, creating the perception of light. According to Petit, a straight-on ray looks like a fuzzy dot, a ray at an angle, a segmented line. Some tracks even have branches like lightning that resemble sparks. Cosmic rays contribute most of the radiation received by astronauts on board the ISS. To date, no one has reached the dosage limit and had to return to a desk job on Earth.
You might think the hull of the space station would keep away cosmic rays, but they’re so tiny and so energetic they pass right through. They can affect electronics too, locking up computers and destroying pixel elements on a camera’s sensor. Petit says you can reboot the computers, but the effect on the sensors is cumulative. Over time, pictures become dotted with pixelly white ‘snow’. Time for a new CCD.
Artistic impression of cosmic rays entering Earth’s atmosphere. Primary rays strike the upper air and create rich showers of less energetic particles. Credit: Asimmetrie/Infn
Studies of cosmic rays on the eyes and bodies of astronauts continues right up through the present with the Alteino-Sileye3 detector used to monitor the radiation environment and light flash phenomenon in the space station.
Cosmic ray flashes remind me of the unexpected benefits of taking a trip to a far-away place. No one considered the possibility (except theoretically), yet by going, we not only discovered a new phenomenon but opened up a lively field of study.