Abengoa's solar power tower, PS10, near Seville, Spain. It is capable of supplying 11 megawatts, or approximately 5,500 households worth of power.Photo: afloresm

Comprised of one or two tall narrow towers surrounded by an enormous field of shimmering mirrors beaming sunlight back up from ground level, these power plants work by essentially the same principle you might have exploited as a child in using a magnifying glass and a hot sunny day to burn holes in the leaves of a backyard playground. A magnifying glass focuses sunlight from a round disk into a single bright dot. A solar power tower's field of mirrors focuses light onto a single water tank high in the air. The concentrated light boils the water, and the steam is used to generate electricity.

In other parts of the world the concept of the solar power tower has gained dazzling momentum as well. Last April, the Spanish company Abengoa commenced operation of a new power tower of its own, dubbed PS20. The power output is still a pittance compared to some of the largest fossil fuel or nuclear plants, but at 20 MW it is currently the largest power tower in existence.

The surge of excitement recently in solar power towers may be grounded on more than hype. Other solar technologies tend to be limited in their promise by cost. Caitlin Cieslik-Miskimena, an eSolar press contact, said that many of the components employed in the company are relatively cheap. She noted, for example, that the mirrors used to collect the Sierra Sun Tower's light are "just a step above a bathroom mirror" in quality. Because they are relatively small, they can also be manufactured to be flat, which is considerably less expensive than the parabolic mirrors used in some other designs.

Nevertheless, solar power towers are just one design in a rich assortment of ideas that people have had for harnessing solar energy. Photovoltaic cells are already used ubiquitously to energize calculators, solar-powered cars, and many satellites, and rapid advances continue to be made in this area. A less flashy form of solar thermal power known as SEGS (Solar Energy Generating Systems) uses curved mirrors to heat long troughs of water. The largest solar power plants in the world today are based on this method. Some companies are even proposing that we exploit solar energy by heating air beneath what amounts to a gigantic clear skirt. (Visit this link for a wild virtual tour of one such proposed plant.)

Time will ultimately tell which (if any) of these will turn out to be commercially viable options as the future marches toward us. Still, we are certain to have a wide array of ideas to explore.

Depiction of Galileo demonstrating his astronomical telescope.

(Almost as famous as this act of opening our eyes to wonders we'd never witnessed, Galileo was tried by the Inquisition for pointing out that there were more things in heaven than were imagined by Church doctrine–but that's another story altogether…)

It's an intriguing fact that, beyond the Sun merely being a bright disk, the Moon a not-so-bright and slightly mottled disk, the stars pinpoints of light and the planets pinpoints of light that move, everything we have learned about the universe and the objects in it we have learned in the last four centuries, since the invention of the telescope and Galileo's putting it to it's most famous use: astronomy.

Galileo saw on the Moon craters, mountains, and valleys, and likened the "uneven, rough… depressions and bulges" to Earth's geographical features. Venus was revealed to undergo lunar-like phases, which provided controversial insight into the layout of the Solar System. Jupiter had four small "star-like" moons that moved around it–which defied Church doctrine holding that everything in the universe goes around the Earth. And Saturn possessed jug-handle-like protrusions, whatever those were!

It may be difficult to imagine what Galileo was feeling when he made these discoveries of things we take for granted. How exciting to peer through that celestial peephole and discover that the Moon is another world, and that there are worlds out there that had never been seen or imagined before. Sure, new discoveries about Mars keep rolling in, and we're finding a new extrasolar planet about every month–but the excitement about these discoveries is tempered by the fact that we already suspected things like these as possibilities. For Galileo, the magnified astronomical sky was practically a blank canvass.

Back to IYA 2009–what's going on? Who's promoting this, and what is being done to celebrate?

NASA is promoting it, and many different organizations (including Chabot and the Eastbay Astronomical Society) are participating in a number of ways: star parties, special programs, special events, and good old fashioned put-your-eye-to-this-telescope-and-gawk public observing activities.
Honestly, there's nothing like looking through a telescope–and it doesn't have to be a large one. I don't doubt that I first became inspired into astronomy when, as a child, my family would take me to Chabot Observatory to look through the telescopes.

When the new Chabot Space & Science Center reopened the telescopes after the move to our present site, I found all of the childhood wonder flooded back when I put my eye to the eyepiece to regard Saturn. There's an excitement that simply can't be achieved by looking at photographs. You just have to experience it for yourself, as Galileo did four centuries ago…

Depiction of a major alignment of
the five visible planets in 1059 BCE.

Photo By Ben Burress

There are some pretty good "lineups" coming soon to skies above you.

First of all, "lineups," or alignments, go on in the heavens all the time, though most often they are alignments of objects too faint to easily notice, if at all. With that said, this summer holds some significant alignments of some of the brightest objects in the sky.

First on my hit list is the upcoming Saturn-Mars "near-miss". Though these two planets are not coming physically close to each other (the closest actual distance they come to each other is about 750 million miles), they will align so closely along the same line of sight that on July 11^th they will appear only ¾ of a degree apart-that's not much greater than the width of a Full Moon. The best time to see this pairing is after sunset on the evenings of July 10, 11, and 12, over the western horizon.

The next big ticket alignment is on August 1^st, when the Moon and the Sun occupy the same spot in the sky-the event we call a Total Solar Eclipse. As it happens, we won't be able to see this eclipse directly from the United States, as it will only be visible in Asia. However, NASA will be broadcasting live coverage of the eclipse from Northern China. We'll be showing NASA's broadcast in our planetarium at Chabot Space and Science Center, in case you'd care to come up and enjoy the spectacle. Don't let the fact that the live event goes on around 4:00 AM keep you away…it's worth getting up for!

A bit further out on the calendar is the September alignment of three planets: Venus, Mars, and Mercury. In the dusky twilight of mid-September evenings the three will be gathering. The closest grouping of the trio is on September 11^th, when they will be within about three degrees of each other-close enough that you can just about cover all three with your thumb. Mercury and Mars won't be very bright in the twilight-but Venus, bright enough to spot easily, can help guide your eye to the other two. Using a pair of binoculars will help a lot-but make sure you don't point them that way until after the Sun sets….

In ancient times (and in some cases not so ancient times), different cultures around the world have viewed alignments like these in different ways. Eclipses-both solar and lunar-were regarded by many cultures as bad omens, or bad occurrences (such as the Sun being devoured by a celestial animal-dragon, dog or other-in the case of a solar eclipse).

Planetary alignments were also given special consideration, sometimes being regarded as auspicious (for good or bad-usually the latter). One major alignment of the five visible planets (February 26, 1953 BCE) was believed to have "mandated" the creation of the Hsia Dynasty in China-the first great Chinese Dynasty. (Then, four centuries later, Mars, Mercury, Jupiter and Saturn apparently conspired to bring down that same dynasty-at least, their alignment on December 20, 1576 BCE was interpreted as an indicator of the dynasty's corruption, and it was overthrown by a revolt of believers…).

However you regard the lining up of celestial bodies (astronomically, astrologically, or aesthetically), these alignments are pleasing to watch, and times to reflect upon the constant and cyclic movement among the heavens. Enjoy….

Magnetic activity on March 27th; white indicates N
magnetic poles, black S. Credit: ESA/SOHO/NASA.

A few blogs back I wrote about the 11-year cycle of ups and downs in solar activity–the Solar Cycle –and how over the last year or so the baton was supposedly passed from Cycle 23 to Cycle 24. But there has been an occurrence on the Sun that suggests we may be in somewhat of a gray zone….

For the past two or three years, the Sun has been downright boring. We set up our Sunspotter telescopes for visitors and try very hard to make what we see seem interesting–"See that perfectly blank circle of light? That’s the Sun! Really it is!"

About a week ago, the tedium was suddenly broken by a train of sunspots that rotated into view on Sun’s disk. Five–count'em– five sunspots! Finally, something to actually look at! And in the eyepiece of our Coronado Hydrogen-Alpha filter telescope there were filaments and plage! What are filaments and plage? Exactly! People wanted to know….

Then came the weird part: these were not Cycle 24 sunspots (I am not the Dread Pirate Roberts…); they were refugees from the supposedly defunct Cycle 23. While the distinction may be a fine point that doesn’t worry most of our visitors, it can still be a good talking point.

So, why were these five sunspots fingered as old solar trekkers rather than members of the next generation? It all comes back to what a solar cycle is–and sunspots, flares, prominences, and plage are merely details: manifestations of the Sun's magnetic convulsions. The Sun, like the Earth, generates an enveloping magnetic field–a big donut with a north and a south magnetic pole. On smaller scales there are plenty of twists and swirls and knots in the field caused by local "hot spots" of magnetic activity–which are what produce features like sunspots in the first place.

At solar maximum–the peak of activity of a solar cycle–the Sun's magnetic poles flip over, or reverse. In fact, it's this reversal that really lets us know when a solar maximum has arrived. (Earth's magnetic field also reverses polarity periodically–although this only happens every 200,000 years, on average.)

At the beginning of a solar cycle, new sunspot activity can be found at high solar latitudes, and as the cycle progresses, activity migrates toward the equator. On a finer nuance, the magnetic polarity of sunspots–which can be N or S, and are usually paired up, like the two ends of a bar magnet –are typically oriented east-to-west on the Sun's surface, one leading to the other as the Sun rotates. Which type of pole (N or S) leads and which trails depends on the overall magnetic "flip" state of the Sun's magnetic field.

To round out this report, the five surprise sunspots of yesterweek were lined up close to the Sun's equator, and the orientation of their magnetic poles bespoke their affiliation with the outgoing magnetic administration (Cycle 23). So far, only a single, high-latitude, reverse-polarity sunspot observed last January has signaled Cycle 24 .

Who knows? Maybe the magnetic candidates of Cycle 24 are still holding primaries, caucuses, and debates and have yet to begin some serious campaigning…

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.

Illustration of a blast of solar wind impacting
Earth's protective magnetic field. Credit: NASA

Did you know that the Sun also has an atmosphere, and that the Earth is inside it? In fact, the Sun's envelope of gases extends well beyond the orbit of Pluto, out to the regions of the solar system where the 3-decade-old Voyager spacecraft are only now reaching.

"Space weather" refers to the conditions in space caused by the outflow of electrically charged gases (plasma) coming from the Sun—what we call the "solar wind." The term "space weather" may conjure images of cosmic tornadoes, astral lightning bursts, and some Star Trek version of a galactic hurricane– but actual space weather is nothing so Earthly and familiar.

First of all, the "air" in space is nothing like the atmosphere we draw our breath from. Earth air, at the surface, is made of nitrogen, oxygen, argon, carbon dioxide, water vapor, and other trace elements, and is relatively dense. "Space air" is mostly hydrogen– ionized hydrogen at that (meaning stripped of its electrons and so electrically charged; the separated electrons are also blowing along in the solar wind).

Second, the gases of the solar wind are extremely rarified. Despite the talk of a solar atmosphere, solar wind, and space weather, space within the solar system is still almost a complete vacuum. At Earth's distance from the Sun, the average density of the solar wind is somewhere between 6 and 9 atoms (mostly hydrogen) per cubic centimeter. If you spread out the gas contained in an ordinary party balloon to this same thinness, it would fill a volume of space over 10 miles across!

Third, the solar wind, for all its sparseness, blows fast! Depending on conditions of space weather, the flow of solar wind past the Earth can speed along anywhere from 200 to 900 kilometers per second! Earth's fastest winds slug along at only a few hundred kilometers per HOUR.

So how does space weather—the changing conditions of the solar wind—affect us on Earth? How might you, personally, have experienced, directly or indirectly, the effects of the Sun's gentle breeze?

The most familiar phenomenon caused by space weather is Earth's beautiful auroras —the northern and southern lights. Interactions between the solar wind and Earth's magnetic field and electrically charged particles trapped in it excite atoms in the upper atmosphere to emit light. And it's not just a softly glowing night light: the most powerful auroras can generate up to a trillion Watts of power!

Solar wind "storms" can not only produce more active auroras, but can cause fluctuations in Earth's magnetic field whose effects can be felt on the ground. These "geomagnetic storms" usually pass unnoticed, perhaps causing a tiny change in the direction that compass needles point– but have also been known to overload electrical power grids and cause blackouts.

In the space around Earth, solar storms have been known to damage or disable satellites, and can put unprotected astronauts at risk. Space walks on the International Space Station are scheduled for times when space weather is – so to speak -"sunny and calm."

Thinking about space weather on Earth might seem like worrying over Atlantic hurricanes here in the Bay Area—but with more and more human activity taking place beyond the confines of our atmosphere, this is a very real and vital concern, and is taken very seriously.

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.

Extreme close-up of the Sun's visible surface,
showing 'bubbling' cells of convecting gas–each the size of
Northern California. credit: Hinode JAXA/NASA/PPARC

First things first: what is a solar cycle, and why is this one number 24? You've probably heard of sunspots and solar flares and disturbances in radio communications caused by solar activity, but had you noticed NOT hearing much about these things in the last two or three years?

The Sun exhibits a cyclic rise and fall in its level of magnetic activity. Being an enormous ball of roiling, circulating plasma (electrically charged gas), the Sun generates powerful magnetic fields in a way similar to how the circulating electricity in an electromagnet creates one.

Over the course of a solar cycle, the intensity and amount of magnetism generated by the Sun increases, like soup warming up on the stove, reaching a violent climax in which twisting, tangling magnetic fields break loose and release their energy in the form of solar flare explosions, coronal mass ejections, and tremendous heating of the solar atmosphere.

Sunspots are surface features formed by the presence of strong magnetic fields, and in general the number of sunspots that can be seen and counted indicate the level of magnetic activity on the Sun. For 400 years, since Galileo first started counting sunspots through his telescope, observers have kept track of sunspot counts, and over time a pattern in their number emerged. On average, the number of sunspot activity peaks every 11 years at a time called solar maximum.

I remember when I first started working at Chabot Space & Science Center, back in 1999/2000, during the last solar maximum. Using our Sunspotter telescopes on public observing days, in teacher workshops, and in my solar summer camp, we could easily count many sunspots-sometimes as many as 20 or more! Those were the days!

In the past two or three summers, however, it's a lucky week to spot just a single sunspot! Most of the time, the Sun's face has been a bland disk with few discernible surface features.

That status quo should start to change, now that we have allegedly reached solar minimum and are stepping onto the uphill slope toward the next maximum, which should happen sometime around 2011 or 2012. If you want to keep tabs on the rising solar activity, and you like lots of graphs and numbers and stuff like that, check out the Solar Cycle 24 website.

Oh, why is this Cycle 24? A 19^th Century astronomer who studied the then newly discovered sunspot cycle, Rudolf Wolf, established the cycle that spanned 1755 to 1766 as Cycle 1…and they've been counting up ever since.

But even in this "nap time" of the Sun, today's modern solar observatories and spacecraft, with their arrays of high-tech cameras and sensors, see plenty on the Sun to keep them busy.

Japan's Hinode spacecraft, launched in 2006, has returned libraries of amazing pictures and movies of solar flares, activity around sunspots, circulating hot gases, fine details of the life and times of magnetic fields…and all of this during solar minimum! I can't wait until the Sun really gets going and Hinode becomes like a camera-happy tourist in Tahiti….

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.