Monday, July 20, 2009

Those Missing Sunspots: The Eclipse Chase

It iss our 2nd full day at our mountain aerie, where we're preparing for Wednesday’s eclipse (July 22 at 9:33 a.m. here in Tianhuangping, China, and 12 hours earlier, 9:33 p.m., on July 21 in New York). I’m here with a team of scientists and students to view and to do research about the solar corona. It's my 49th solar eclipse, and the 29th total eclipse. (A dozen of the others were annular, when a ring of everyday sunlight remains, and a few were merely partial.) We are coming up on the 50th anniversary of my first eclipse, which I saw as a freshman at Harvard under the guidance of the eclipse expert Donald Menzel.

We look at the sky carefully all day, watching the clouds come and go. At eclipse time yesterday, the sun was in a thin bank of clouds, through which we would have seen the corona; a fist’s width to the side, a quarter of the sky was pure blue. This morning (it is now 5:45 a.m., but we have been up for hours; the 12-hour time-zone change is brutal) we see blue sky and an overlay of clouds. But only 9:33 to 9:39 a.m. on Wednesday will count.

The longest total solar eclipse this century will begin on July 22 in India, sweeping east across China and into the Pacific Ocean. Blogging about the event for TierneyLab is Jay M. Pasachoff, a Williams College astronomer and veteran eclipse chaser who has planted himself and some colleagues on a mountain outside Hangzhou, China, to see and study the eclipse.

I just checked not only the weather outside my window (which overlooks dramatically deep valleys and wooded mountains) but also the space weather. “Space weather” is the current name for the relationship between the Sun and the Earth, since the Sun gives off particles in an outflow called the solar wind and bursts of X-rays and other radiation, affecting the Earth. Today’s monitoring at shows that there are no sunspots on the Sun — again. More detailed monitoring at shows that other images of the solar surface, in X-rays, magnetic field, hydrogen light and ultraviolet light, are all smooth rather than showing bright areas that mark the sunspot regions. Sunspots are places on the Sun where the magnetic field is thousands of times stronger than the average magnetic field. But there have been hardly any for about 2 years now; the Sun has been blank for more than 3 quarters of the time. This is very unusual, even for a low phase in the approximately 11-year sunspot cycle. And we've been in this low phase for at least 12 and a half years, getting to a worrisome point. Nobody knows why it is taken so long — or even definitively if sunspots will reappear.

Scientists are particularly interested because of work by the recently deceased astronomer Jack Eddy, who found a period in the early 1700’s where there were no sunspots for decades. That period corresponded to a cool period, at least in Europe, known as the Little Ice Age. Nowadays, scientists monitor the “total solar irradiance” (it used to be called the solar constant, but it turned out not to be constant). It's about 1/10 of a percent less at sunspot minimum than at sunspot maximum, which has to be taken into account in models of global warming. The effect is much too small compared with our human contributions to the atmosphere to be important for global warming calculations, but it should be included in the models.

Tianchi, the town near here, means “heavenly lake” (or high-altitude lake). We're at the end of a windy road with many hairpin turns, and we hope thus to be away from the bustle of downtown Hangzhou. (However, I have given a number of TV and newspaper interviews, and we hope that all 20 million people from Shanghai don’t decide to try to get here because the professional astronomers are here.)

Yesterday, my team unpacked a lot of the shipping containers we brought and set up the telescope mounts we have borrowed from the local Celestron telescope dealer through Lin Lan, a teacher at Hangzhou High School who runs a wonderful astronomy club there. Some of her students are with us, along with 5 of our Williams college and visiting undergraduates. I work on the scientific experiments here with Bryce Babcock, a physicist at Williams College who is a genius with electronics and computers. He is supervising 2 of our students, Katie DuPré and Yung Hsien Ng Tam (known as Caroline) in setting up and testing our 2 main systems, meant to search for oscillations in small loops of the solar corona. Our equipment is sensitive to very short periods, only about 1 variation per second, by taking images at 10 times per second through a very special filter that passes only light from million-degree coronal gas. So we should have 600 exposures per minute or over 3,300 exposures on each of 2 cameras. We therefore hope to have lots of data to study when we get back to Williamstown. Our hope is that our search for oscillations will distinguish among theories of how the solar corona gets to be millions of degrees.


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