Date: November 14, 2011
Title: Countdown for Upcoming Solar Eclipses
Podcaster: Jay Pasachoff
Link: App for information on the Sun: www.3dsun.org
Description: Noted astronomer Dr. Jay Pasachoff talks about the upcoming solar eclipses through 2017.
Bio: Jay Pasachoff, Chair of the International Astronomical Union’s Working Group on Eclipses, is Field Memorial Professor of Astronomy at Williams College. He has viewed 53 solar eclipses, and is an expert on both their use for scientific observations and their use for public education. Pasachoff is past president of the International Astronomical Union’s Commission on Education and Development and Chair-Elect of the Historical Astronomy Division of the American Astronomical Society. He received the Education Prize of the American Astronomical Society. Pasachoff is the author of textbooks on astronomy and of the Field Guide to the Stars and Planets, and co-author of Nearest Star: The Surprising Science of Our Sun and, on a more technical level, The Solar Corona. His research at the two eclipses of 2012 is supported in part by a grant from the National Science Foundation.
Sponsor: This episode of “365 Days of Astronomy” has been sponsored by the Physics Department at Eastern Illinois University: “Caring faculty guiding students through teaching and research” at www.eiu.edu/~physics/.
The countdown is ticking towards the next total solar eclipse of the sun. On November 13th, 2012, the shadow of the moon will sweep across the Earth, but only limited parts of that path will be accessible. Many people therefore are planning to go to the only place where the eclipse will cross land, in Northeastern Australia.
When the path of the shadow leaves land, early in the morning, on November 13th, it will have the sun only about 12 degrees high in the sky, so further back in the Australian outback is less desirable. We eclipsers will therefore be clustered along the coast of Australia and Queensland in places like the city of Cairns and about an hour north in the city of Port Douglas.
There have been a series of eclipses that have recently been observed with wonderful coordination between ground based observing and the great satellites in space.
NASA now has aloft the Solar Dynamics Observatory, which is sending down phenomenal amounts of data. It takes eight images every twelve seconds through different filters that reveal the sun at high resolution. Those pictures in the extreme ultraviolet reveal aspects of the solar corona, because we don’t see the ultraviolet like that on Earth. It doesn’t come through the Earth’s atmosphere so we need the eclipse results to coordinate with the space results.
In 2012, the rainforest at the edge of Port Douglas has not been entirely cut back and between the city of Fort Douglas and the hotels and the view of the eclipse 12 degrees high in the sky, there are some feet or meters of tall trees. So people have been told to go onto the beach which is not a desirable thing to do if you have fancy cameras or telescopes. Therefore my own group has actually hired a house on a hill, about fifteen miles north of Fort Douglas. It has a sweeping view over the shore and over the ocean so we do expect to be able to see the shadow of the moon sweep in beautifully and then the eclipse itself in the sky.
We do want to correlate with not only the Solar Dynamics Observatory’s images but also the STEREO images that are taken from a pair of spacecraft, STEREO. STEREO AHEAD, also known as the STEREO A, and STEREO BEHIND, known as STEREO B. Those two spacecraft are now halfway around the sun in orbits that are close to the Earth’s orbit so they view the sun from quite different angles, and actually together with the views from the Earth, we now see the sun all the way around.
We, therefore, are never again going to be surprised by a big sunspot or a big active region that comes around from the far side. There’s a wonderful app for an iPad or iPhone, http://3dsun.org/ , in fact, that allows you to see the whole sun any day and move around it just by sliding your finger around the screen.
We are now in a rising phase of the sunspot cycle. The sunspot cycle, as many people know, is an eleven-year cycle, but really, it varies quite a lot between about eight years and twelve years. In 2008 and 2009, we had the deepest minimum we had in about a hundred years with no sunspots at all on the sun for about 75% of the time a year before the 2009 eclipse.
When there are very few sunspots on the sun, that means there are very few active sites on the sun, and that in turn means there are very few streamers in the corona. The streamers that there are, are close to the equator of the sun, and therefore at sunspot minimum. The shape of the corona looks overall pretty out of round, pretty elliptical.
Now, we are in a rising phase of the sunspot cycle, so there are dozens of sunspots on the sun all the time. This means that there will be streamers at higher latitudes as well and the overall shape of the corona will look rounder. We are eager to see that higher shape at the eclipse in 2012.
I’ve been working with some colleagues from Greece who’ve been taking wonderful spectra of the corona. One thing that we can do with spectra is look at iron that is heated so high that it has lost 13 of its 26 electrons. It gives off a spectral line in the green, and also from iron that has lost 9 of its electrons, it gives off a spectral line in the red. By looking at the ratio of the intensities of those two spectral lines, we can tell the overall temperature of the corona.
Comparing what we saw in 2008 at the eclipse in Siberia, confirmed by what we saw through clouds in 2009 in China, and with the eclipse in 2010 that we observed from Easter Island, when the sunspot minimum was just about over, we could see that the temperature has increased since the sunspot minimum already because the higher temperature line, the iron fourteen line [Fe XIV], the so-called green line, was more intense at the later eclipse. We expect to see it intensify further in 2012.
After this total solar eclipse of November thirteenth, 2012, we’ll actually be back in the Australian outback, about six months after that for an annular eclipse in May 2013. An annular eclipse, you may recall, is when the moon in its elliptical orbit is a little further from the Earth than average and so it doesn’t look quite as big in the sky. An annulus, a ring of sunlight, thus remains. It’s fun to see, an annular eclipse, but one doesn’t get the daylight going away, becoming dark as night in the middle of the day as you do for a total eclipse, so one has to do a different type of thing if you want to do scientific research.
We are actually arranging to do such scientific research at the earlier annular eclipse which will take place in May 20th this year, before the total eclipse. That annular eclipse will begin in Japan, and go across the Pacific Ocean, hit the United States in Northern California, in Southern Oregon, and will sweep across Utah and New Mexico and Nevada and end up near Lubbock, Texas. The whole western United States, in the late afternoon, on May 20th, will have a partial eclipse, a pretty substantial partial eclipse, with almost all the sun obscured and it will last until sunset. We have arranged to use radio telescopes, such as the one at Goldstone, California and others that are at the Owens Valley in California and possibly also the Very Large Array of radio telescopes that is run by the National Radio Astronomy Observatory near Socorro, New Mexico.
There are many high precision observations in the ultraviolet and the visible from space but fewer high resolution observations are available in the radio part of the spectrum. So with these radio telescopes we can watch to see when exactly the moon covers the active regions on the sun that give off a lot of radio radiation since we know exactly where the advancing edge of the moon is. When those radio noise bursts get quiet, we know that the advancing edge of the moon has just covered them and when they come back again we know that the trailing edge of the moon has just uncovered them.
So we hope to get some high precision observations of the active regions that we now know will be on the sun at the time and be able to compare the details of those active regions with the direct observations in the ultraviolet.
There are eclipses of the sun about every year and a half for a total eclipse, and every year and a half for an annular eclipse and then sometimes for partial eclipses. In the year 2011, there are four partial eclipses, no total or annular eclipse. The next partial eclipse will be in a couple of weeks but will largely take place in the ocean off the coast of Antarctica and partial phases will be visible from the southern island of New Zealand, where I am going, and from part of Tasmania, southern part of Australia, and from the southern part of South Africa. And then some substantial fraction of the sun, up to about half, can be visible from those locations which I am looking forward to seeing.
Many people are looking forward, especially, to the August 21, 2017 eclipse that will cross the whole United States with a band of totality and which will have partial phases visible through, really, the whole United States. Not only continental United States but even Alaska and Hawaii. But just knowing that an eclipse will come nearer to us in five years will not be enough to keep a lot of amateur astronomers and just ordinary tourists, not to mention professional astronomers from the November 13th, 2012 total eclipse in Australia.
End of podcast:
365 Days of Astronomy
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