Catching a Few Rays : Astronomers Attempt to Shed Light on Earth’s Climate by Studying the Sun
Most astronomers yearn for clear, dark nights and a mountaintop from which to scan the skies.
Gary Chapman, a professor of astronomy and physics at California State University, Northridge, longs for smoggy, sunny San Fernando Valley days.
And he is perfectly happy with the location of his white-domed observatory, tucked away on low ground among the power lines and ponds at the Los Angeles Reservoir west of Sylmar.
“Traditionally, if you’re an astronomer, you have to go far away, drive up a mountain and be cold and miserable,” Chapman said. In contrast, he has a 15-minute drive each morning from the CSUN campus to the observatory, which is at the end of a winding road, bordered by blooming azaleas, that cuts across Los Angeles Department of Water and Power property.
He can work during the day because the celestial object that he studies is the sun.
Chapman and a team of astronomers, undergraduates and technicians are doing research on the sun’s turbulent behavior that may help confirm, among other things, whether Earth is headed for a warm, destructive greenhouse effect.
Their work focuses on sunspots, dark blemishes on the sun’s blazing surface that materialize and disappear in a mysteriously regular cycle.
The powerful magnetic forces and radiation that accompany these solar storms can disrupt electronic communications and cause power failures on Earth, and may also influence Earth’s climate, said Chapman, who is the observatory’s director.
Ironically, the same stagnant, smoggy summer air that often makes it difficult to see the mountains ringing the San Fernando Valley actually can provide “ideal” conditions for observing the surface of the sun, about 93 million miles away, Chapman said.
The key is the atmospheric stability that comes with smoggy conditions. On clear, blustery days, the many layers of the atmosphere become turbulent. “Parts of a beam of light get tossed around,” Chapman said.
The smog can get too thick, however, lowering light levels at midday as much as 30% and closing down observations, Chapman said. But generally, smog acts like a filter on a camera, merely cutting back on the total amount of sunlight.
The San Fernando Observatory was donated to Cal State Northridge in 1976, seven years after it was built by an El Segundo research laboratory with close ties to the Air Force.
It was originally designed to study solar flares--bursts of radiation and particles that seem to be produced by sunspots and that are flung into space with the power of thousands of exploding hydrogen bombs--with the thought that the flares could imperil space missions. But, as the Air Force became less involved with manned space missions, the need for a solar observatory died.
The main building houses two telescopes--specially designed to withstand the sun’s intense heat--beneath a gleaming white dome supported by a central pillar and four leg-like struts. It resembles an overgrown version of the lunar lander from which Neil Armstrong took his moon walk in 1969.
Sunlight enters the telescopes and is focused by a series of mirrors and lenses. The largest telescope, 24 inches in diameter and about 15 feet long, can pick out features on the sun’s surface that are the size of Arizona.
“The absolute limit would be to see something the size of Los Angeles County,” Chapman said. Considering that an average sunspot is much larger than the entire planet Earth, something the size of Arizona is a fairly fine detail.
A few yards away, the aptly named “little dome” contains a third, smaller telescope that also records details of the sun digitally, so that they can be manipulated and analyzed by powerful computers back at the CSUN campus.
Viewed in the noonday sky, the sun appears to be as constant and unwavering as a brilliant spotlight. But its surface, when brought close by the telescopes, is a violent sea of gases that slowly roil and bubble as pockets of heat burst upward, fueled by thermonuclear reactions in the sun’s core.
Deep within the sun, unknown forces interact to create the equivalent of a massive electromagnet. Sunspots seem to occur where enormous concentrations of this magnetic energy--9,000 times greater than the magnetic force on Earth that directs a compass needle--emanate from the surface, Chapman said. The sun’s outer layers of gas are distorted by the magnetic field around sunspots, producing patterns similar to those seen when iron filings are sprinkled around a magnet.
The sunspots look like cavernous eddies, but they are actually dark only because they are cool, about 4,000 degrees cooler than the surrounding glowing gas. No one knows why they are cool, Chapman said.
Every 11 years, almost without exception throughout recorded history, the sun’s surface becomes pocked with sunspots. Sunspots also occur at other times, but most are clustered during these peaks, called solar maximums.
The last solar maximum came in 1980. Now is the season of the “quiet sun,” a period of relative calm that is used by astronomers to analyze the billions of bits of data collected in previous years, Chapman said.
A prime goal of Chapman--and his colleagues John Lawrence and Adrian Herzog--is to find any link between the cycle of sunspot activity and changes in climate here on Earth. The sun heats the land, water and air, setting in motion global weather patterns. Even a minor fluctuation in the total output of solar energy can have substantial consequences.
One key to this, Chapman said, is the study of the energy balance of sunspots. The cool sunspots are almost always surrounded by bright patches, called faculae, that are hotter than the surrounding gas. The CSUN astronomers are using computers to map and measure the bright and dark areas, which correspond to heat and cold, to see if they equal each other.
If the coolness of the sunspots is balanced by the extra heat in the faculae, the net effect of sunspot activity on Earth’s climate--even at solar maximum--is probably negligible, Chapman said. But if sunspots do reduce the sun’s total energy output, that could confirm some tentative climatic connections. Some scientists, for instance, have thought for years that there is a link between a 22-year cycle of drought in the Midwest and the 11-year sunspot cycle.
Accurate measurements of changes in the sun’s energy output are also needed to understand other subtle influences on Earth’s climate, including the possibility that the planet is undergoing progressive warming because of carbon dioxide and other gases added to the atmosphere by man--the greenhouse effect.
“You have to be able to separate solar changes from man-made changes,” Chapman said. “If man is mucking up the environment, how do you know it’s changing the climate of Earth if you can’t subtract out any solar factor?”
Data gathered by the San Fernando Observatory is being compared to that from other observatories and from the Solar Maximum Satellite, which was launched into orbit in 1980 to make long-term measurements of the total output of energy from the sun--everything from X-rays to ultraviolet light.
Even now, in the time of the quiet sun, there are three or more people at the observatory almost every day, recording several different types of images.