There are so many different kinds of light or electromagnetic radiation out there, and to see them as clearly as we see the visual world, you need a special instrument for each one. Radios decode invisible radio waves sent from a transmitter into music and news. A room filled with people slowly heats up from infrared radiation or heat radiating from our bodies. You’ll need a special infrared detector to actually see that heat, otherwise you’ll have to do with feeling sweaty. Our eyes detect the colors of the rainbow, which occupies a small section of the electromagnetic spectrum. Visual light has a wavelength of about 1/50,000 of an inch. That’s the distance between one crest to the next as light travels from here to there in the shape of a very regular, repeating wave. We see light’s rainbow colors and not radio waves or X-rays, because our eyes evolved on a planet around a star, and stars emit most of their light in the visual portion of the spectrum. We are attuned to the sun.
UV light waves are two orders of magnitude shorter than the rainbow spectrum, and gamma rays are only 4 billionths of an inch or as long as subatomic particles. Light of short wavelength has a higher frequency, meaning its waves are packed together more tightly. Since we cannot deny the laws of physics, scientists long ago determined that light’s energy is proportional to its frequency. The higher the frequency, the more energy. No one’s ever going to get a sunburn standing in front of a radio antenna bathing in long wavelength-low frequency radio light, but too much exposure to short wavelength-higher frequency ultraviolet light from the sun will literally burn your skin tissues. Thankfully, our atmosphere and ozone layer protects us from much of the sun’s UV light as well as higher frequency (and more damaging) X-ray and gamma ray light.
To see all the universe has to offer in terms of light, scientists, working with engineers, develop and loft space-based telescopes above the atmosphere into Earth orbit, where they’re free to study stars, galaxies and black holes in their wavelength of choice. Things invisible to the eye suddenly stare you in the face when viewed in, literally, a different light. Infrared light penetrates the dusty cocoons surrounding newborn stars, allowing us to catch them right at birth. X-rays and gamma rays are shot into space by highly energetic events like gamma ray bursts or when matter gets sucked down into the maw of a black hole.
Just this week, NASA announced that its Fermi Gamma-ray Space Telescope detected a massive new structure in the Milky Way galaxy that may have created by an eruption from the supermassive black hole in the galactic core. Two gigantic bubbles, each 50,000 light years across, extend north and south of the galaxy’s center. If you could see them with your eyes, they’d span more than half the sky from the constellation Virgo (visible in spring) to Grus the Crane, a fall constellation. The structure’s shape and emissions suggest it was formed as a result of a large and relatively rapid energy release. Astronomers are considering two possibilities: jets of particles from the past powered by matter that fell into the Milky Way’s central black hole or the outflow of gas from a long-ago burst of star formation. Either one is exciting to contemplate. And neither would be known were it not for scientists opening a window on the gamma ray end of light’s grand spectrum.
A final observers’ note – if it’s clear by you this evening, you’ll see the first quarter moon make a nifty triangle with Jupiter and the bright star Fomalhaut (FOME-uh-low) in the southern fish or Piscis Austrinus. Fomalhaut is the brightest star so far discovered that’s orbited by an extrasolar planet.