May. 07, 2015

What Does the Sun Do? Solar Experts Respond

by Julie Leibach

Click to enlarge images
As part of this installment of Science Club—called #ExplaintheSun—we asked scientists and other individuals with a solar interest to answer the question: What does the sun do? Their responses highlight a variety of starring roles in everything from space weather to energy production. Got an answer to add? Take to the comments, or tweet a description using the hashtag #ExplaintheSun. 
Astronomical Insight
By Dean Regas
Outreach astronomer, Cincinnati Observatory
Co-host of the syndicated PBS program "Star Gazers"
The sun teaches.
The repetition of the sun rising, setting, and rising again became the primary cycle to life on Earth. Call that a “day.” Our prehistoric ancestors imprinted this pattern into our very nature. The first rays of light at sunrise made a welcome sight and led to a day of hunting, gathering, and farming. Ancient observers monitored the way light fell at different times of the day and how cast shadows moved, shortened, and lengthened. As the sun set, they noted the emergence of different animals and wondered how long it would be before the sun would return. After a few thousand days, they comprehended the sun’s longer pattern—call that a “year”—and from then on, every day of every year, the first astronomers could predict when and where the morning sun would rise and the evening sun would set. The sun taught us to be scientists.
Energizing the World
By Ernest Moniz
United States Secretary of Energy
What does the sun do? Let’s talk sun and energy. First, the sun’s surface temperature—you know, it’s about 10,000 degrees Fahrenheit, so it’s a big energy source, driven by fusing together hydrogen. We’re trying to harness that fusion process on Earth, but it’s very hard and expensive. In the meantime, we use the light from the sun here on Earth to make energy directly. In one hour, the solar energy hitting Earth is enough to meet the world’s energy needs for about a year. Solar energy technology is making great strides, and we think it will be a major source of carbon-free electricity in the years ahead as the costs keep falling, and energy storage allows us to use the electricity even when the sun is not shining.
Space Weather Instigator
By Douglas Biesecker
NOAA/NWS/Space Weather Prediction Center
The sun causes weather in space, but if that’s all there was to it, then only astronauts would need to worry about it. However, this weather in space, called space weather, is really describing the sun’s variable impact on Earth. The visible manifestation of space weather is the aurora. When you are hearing reports of aurora, recognize that the same storm is felt by operators of the electric power grid, commercial and private airlines, and precision GPS users such as surveyors, oil drillers, and farmers. Solar flares from the sun, primarily from bursts of x-rays, cause problems for airlines, and also ships at sea, that depend on high-frequency radio transmitters. (Don’t worry, our atmosphere protects us from the x-rays.) Huge clouds of material (plasma) and magnetic field erupt from the sun, and when these clouds, known as coronal mass ejections, hit the Earth they not only cause the aurora, but also put the electric power grid at risk and can make GPS unreliable.
The NOAA/NWS/Space Weather Prediction Center monitors the sun and forecasts space weather. Providing power grid operators, airlines, GPS users, emergency managers, and many others with space weather forecasts helps to ensure the lights stay on and other impacted users can take actions to minimize the threat.
A Photosynthetic Perspective
By Barbara A. Ambrose, Ph.D.
Cullman Associate Curator, Plant Genomics
The New York Botanical Garden
The sun provides energy. Plants transform the sun’s energy into stored chemical energy during photosynthesis. This is an amazing process in which plants take carbon dioxide, water, and the sun’s photons, and produce carbohydrates and oxygen. These carbohydrates are the stored chemical energy that allows plants to grow and develop into the food we eat and the flowers we enjoy. Plants have evolved for hundreds of millions of years to harness the energy of the sun efficiently and effectively, something we humans have yet to perfect. What’s really cool is that a byproduct of this reaction is oxygen—the air we need to breathe.
Spreading Joy
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
Solar Photographer


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.)
(Em)powered Exploration
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.



About Julie Leibach

Julie is the managing editor of She is a huge fan of sleep and chocolate. Follow her @julieleibach.

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