By Richard Friedman
Professor, Clinical Psychiatry
Director, Psychopharmacology Clinic
Weill Cornell Medical College
There is a reason why the sun makes us happy, why we are drawn towards people with sunny dispositions, and why so many of us are deeply affected by the seasons: sunlight has a biologically profound effect on our mood.
As the days shorten, millions begin to feel depressed, withdrawn and sluggish—sleeping and eating more and having more sex. Come spring and summer, these symptoms vanish, only to return the following autumn.
I just described seasonal depression, which affects about 10 percent of adults living in northern latitudes, and only about 1.5 percent of those in southern regions like Florida.
People with seasonal depression behave a lot like hibernating animals in the winter. It turns out that our brains track seasonal sunlight patterns with melatonin, a chemical turned on by darkness and off by light. Experiments show that people with seasonal depression have a longer duration of nocturnal melatonin secretion in the winter than in the summer, just like other mammals with seasonal hibernating behavior.
Those who don’t have a seasonal change in mood show no seasonal fluctuation in melatonin secretion. The likely reason is exposure to industrial light, which can suppress melatonin. By keeping artificial light constant during the year, we can suppress the “natural” variation in melatonin experienced by those with seasonal depression.
There was probably once a survival advantage, a few hundred thousand years back, to slowing down and conserving energy—sleeping and eating more—in winter. Could people with seasonal depression be the unlucky descendants of those well-adapted hominids?
Perhaps, but no one with seasonal depression has to wait for spring and summer to feel better. My colleague Dr. Normal Rosenthal, a professor of clinical psychiatry
at the Georgetown Medical School, showed conclusively that artificial bright light in the early morning is a powerful, fast, and effective treatment for seasonal depression.
So we can trick your brain—somewhat—with artificial light, if you’ve got seasonal depression, into thinking it’s a kind of perpetual spring and summer, even with the waning of sunlight in the fall and winter.
Still, it’s hard to beat the medicinal effect of sunshine.
Through the Lens
By Alan Friedman
So I say to the sun, “Go ahead…make my day.” And it does and will continue to do so for five billion years.
I know a little about the cosmos. I know that our sun is a totally average yellow star and the earth a pale blue, rocky dot just like a billion other planets. So let’s concentrate on what is special. Of the countless stars in the sky, the sun is the only one I will ever see up close and personal. It is large enough in my small telescope to reveal an incredible wealth of features—a rotating, constantly changing nuclear furnace.
As I take pictures
of its earthward face, I ponder the magic of my ordinariness. How I get to swim in lakes with liquid water. How our moon and sun are balanced at just the right distance so each appears the same size in our sky. And when they line up just right, give us the solar eclipse and a fleeting glimpse of the outer atmosphere of our neighborhood star.
In its brilliance, the sun defies more than a momentary glimpse. But today, with safe solar filters available to the amateur astronomer on a budget, I can photograph and share the workings of the distant universe from my own backyard. How cool is that?! (For more on Alan Friedman's photography, check out this SciFri article
By Les Johnson
Author, scientist, and NASA technologist
Not only does the sun power Earth and those of us who reside here, but it also provides or has provided power for most of our past, present, and future spacecraft exploring the solar system. Photovoltaic arrays have provided electrical power for robotic and human spacecraft since the earliest days of the Space Age, with the flight of the USA’s Vanguard 1 in 1958. The International Space Station’s solar arrays generate up to 90 kilowatts of power for the astronauts who have resided there continuously for nearly 15 years. Using the sun to provide power for our spacecraft is well understood and in wide use.
Only now are we beginning to think more broadly about the sun and how it can be used to provide spacecraft propulsion as well as power. Some spacecraft use their generated solar power to drive electric propulsion systems for station-keeping and for moving from place to place. Electric propulsion uses electric and magnetic fields to accelerate propellant instead of chemical combustion upon which traditional rocket engines rely. This makes electric propulsion systems much more efficient than chemical rockets (up to 10 times as efficient!) and has enabled the Dawn Spacecraft to visit two main belt asteroids—a feat that would have been impossible with less efficient, conventional chemical rockets.
In 2010, the Japanese Aerospace Exploration Agency (JAXA), entered the record books by using sunlight to directly provide propulsion for their IKAROS spacecraft without first generating electrical power. Taking advantage of an interesting property of light—the fact that photons have momentum—the IKAROS spacecraft deployed a large, lightweight reflective sail which used the momentum transferred to it from reflected sunlight to navigate within the inner solar system. Using these solar sails, it is theoretically possible to navigate throughout the inner solar system without using any rocket propellant. NASA and the space advocacy group, The Planetary Society, plan to fly spacecraft propelled by solar sails within the next few years.
The sun is also sending a continuous stream of plasma (a mixture of charged particles, mostly positively charged protons and negatively charged electrons) outward and into the farthest reaches of the solar system. An innovative group of space scientists and engineers are now proposing that a spacecraft equipped with multiple, very long, positively charged wires sail this solar wind as yet another means of navigating through space. Since positive charges repel each other, the positively charged wires of the spacecraft would be repelled by the solar wind protons, dragging the spacecraft along with them for the ride. Since the solar wind is traveling at speeds up to 900 kilometers per second, spacecraft equipped with these electric sails could attain speeds higher than is possible with convention or electric propulsion, or even solar sails driven by sunlight.
As we learn more about the sun, people are finding more and more ways to use it as a resource for enhancing and enabling our exploration of the solar system. Given the innovative ideas emerging for using sunlight and the solar wind for propelling our spacecraft, I suspect the sun, which dominates virtually every aspect of life within the solar system, has yet more to teach us.