Gazing up at the Man in the Star?

Using a suite of four telescopes, astronomers have captured an image of Altair, one of the closest stars to our own and a fixture in the summer sky.

While astronomers have recently imaged a few of the enormous, dying, red-giant stars, this is the first time anyone has seen the surface of a relatively tiny hydrogen-burning star like our own sun.

"The galaxy is shaped by the effects of relatively rare but powerful hot, rapidly rotating stars," says John Monnier of the University of Michigan, the lead author on the study that will appear on Science Express on May 31, 2007. "These stars have more in common with Altair than our own sun and understanding Altair will allow us to better understand how these influential stars scattered throughout the galaxy operate."

Monnier was part of an international team of astronomers that captured the image using four of the six telescopes at a facility on Mt. Wilson, Calif., operated by the Center for High Angular Resolution Astronomy (CHARA) at Georgia State University in Atlanta with partial support from the National Science Foundation (NSF).

The CHARA telescopes were able to make the breakthrough observation because they were outfitted with a novel system to clean up some of the distortions from Earth's atmosphere, a technology called the Michigan Infrared Combiner, developed with NSF support at the University of Michigan in Ann Arbor. Recent advances in fiber optic telecommunication technology made this new combiner possible.

"For looking at optical or infrared wavelengths of light, the CHARA telescope array has the world's longest spacing between telescopes and therefore the greatest ability to zoom in on the stars," adds Hal McAlister, CHARA director and a professor of astronomy at Georgia State.

Until now, astronomers could gather tremendous amounts of data from stars, but could not capture images of what the stars looked like. Even to the largest telescopes, stars looked like the points of light we all see when we peer up into the night sky.

Using the telescopes as an interferometer--a multi-telescope system that combines information from small, distantly spaced telescopes to create a picture as if taken from one large telescope--the researchers captured infrared lightwaves as if from a giant telescope 265 meters by 195 meters in dimension (100 times the size of the mirror on NASA's Hubble telescope and roughly 25 times the resolution).

"Without the interferometer, the ability to obtain such detailed images would not be possible with today's existing telescopes--or even the planned 30-meter telescopes," says Julian Christou, one of the NSF officers overseeing the research. "The critical component of the CHARA system is the beam combiner which allows the light from the individual small telescopes to be mixed together, which up to now had only been successfully used with radio telescopes such as the Very Large Array near Socorro, N.M."

The discovery is helping to answer questions about stars while raising others, particularly when researchers compare long-standing models to the new observations.

For example, Altair is a speedily spinning "rapid rotator", just like Vega, one of Altair's partners (with the slow-spinning supergiant Deneb) in the Summer Triangle in the night sky.

Altair spins so quickly, about 300 kilometers per second at its equator, that it's shape is distorted: the star is a full 22 percent wider than it is tall. The new telescope measurements confirmed the oblong shape, yet showed slightly different surface temperature patterns than what models predicted.

Altair is one of the closest stars in our neighborhood, only about 15 light years away, and the researchers hope to image Vega as well as more distant stars in the future.

"Imaging stars is just the start.We are going to next apply this technology to imaging extrasolar planets around nearby stars," said Ming Zhao, an astronomy graduate student at Michigan who carried out the detailed stellar modeling.

NSF supported this research through awards 0606958 and 0352723, along with a number of awards totaling nearly $6.5 million to help construct CHARA.

For additional information, see the press releases at the University of Michigan (http://www.umich.edu/news/) and Georgia State University (http://www2.gsu.edu/~wwwexa/news/).

Additional graphics are available at: http://www.astro.lsa.umich.edu/~monnier/Local/altair2007.html

Sheeez people. If you wish to worship yourselves go for it but stop addressing me k?

No, that's not OK. You threw down the gauntlet, and cannot call foul when someone picks it up. If you don't want to be addressed, and in particular called on the ignorance you spout, the internet is not for you.

Beyond that, there may be people reading who also don't know the answers to the questions you raise, but who actually do want to know what they are. For their benefit, and not for yours, I offer the following:

Q: What the sun is made out of?

A: It's mostly a plasma of hydrogen and helium, plus carbon, oxygen, nitrogen and other elements.

Q: How do you know it's a plasma?

A: Because we can measure the temperature of the sun's surface, by the shape of the blackbody curve. It's around 6000 Kelvin. That's enough to render any of those elements into a plasma.

Q: How do you know what elements make up the plasma?

A: We know it because of the spectral lines in the light from the sun. The frequencies tell us what atoms are present, and their brightness tells us how much.

Q: How do you know what each those lines are?

A: Because we measured them in the laboratory beforehand. There was an exception to this, however: there was a series of lines in the solar spectrum that had never been seen before. The frequencies of those lines matched what theory predicted for the missing element 2 of the Periodic Table. They named this newly discovered element "Helium" after the sun, where it was discovered. Only later was it found on Earth.

Q: How do you know that the material between the Earth and the Sun isn't responsible for the spectral lines?

A: For one thing, the intervening material isn't bright enough; the sun puts out a lot of light, in case you hadn't noticed. But more importantly, we can measure the stuff between the Earth and the sun. Take Venus, for example. We know the chemical composition of its atmosphere because we've sent probes down into it and measured it. We can also measure its spectral lines from Earth. The two agree, so that's a firm foundation. Fair enough? Well, we can also use Venus to probe what's between the Earth and the sun: as Venus swings around its orbit, sometimes it's on the near side of the sun, and sometimes it's on the far side. As it passes behind the sun, we're looking right past the edge of the sun, through all the intervening material. By observing the changes in the spectrum of Venus, as we see it from Earth, we can measure that intervening material.

Q: But still, wouldn't it be more reliable to have a sample of the sun that you could measure directly in the lab?

A: Not really, because if we had it in the lab, we'd determine its composition by the same spectrographic technique. A spectrum at arm's length is no better than one at 100 million miles. That said, we do have such samples. The sun blows off huge bubbles of its own material out into space, all the time. We have probes out there that collect samples and analyze them.

Q: How do you know that hydrogen fusion powers the sun?

A: Really, it's the only power source we know about that can actually do the job. The sun puts out a lot of power. The only other source we know about that can do that is gravitational collapse, but first, the sun would cool too rapidly, and second, that would be inconsistent with what we see in other stars in the sky. More importantly, however, we can measure those fusion reactions directly by the neutrinos that come out of the sun.

Q: How do those neutrinos tell you what reactions are going on in the sun?

A: They tell us that by their energies. Different nuclear reactions produce neutrinos of different energies. The neutrinos from the sun indicate proton fusion into helium, catalyzed by Beryllium and Boron.

Q: How do you know that those neutrinos come from the sun, and not from elsewhere in space?

A: Because we can tell what direction the neutrinos are coming from. In fact, we have enough of them to produce a neutrino image of the sun.

Q: Isn't there a solar neutrino deficit, where they don't observe as many neutrinos as theory predicts?

A: Not anymore. The Sudbury Neutrino Observatory resolved that problem. Previous detectors were only sensitive to one type of neutrino, but if you measure all of the neutrinos coming from the sun, the number is in accordance with what is predicted by the standard solar model.

"I don’t know why Joseph Lockyer’s voyage is not more well known. I can only suppose it is due to persecution of news reporters and scientists by the solar phlogiston contingent ..."

There are those factors, of course, but I tend to think it has more to do with the fact that most of the official papers were written in French, and submitted to the French Academie. (Note: To really appreciate the flavor of the expedition, it is necessary to read the original documents, in French of course, as no acceptable translation has been provided.)

News of the expedition was then swept up in a bit of confusing unpleasantness following the turn of the previous century, and world respect never quite got back to what it was for the French.

Then there is the matter of the Chinese involvement. For "serious" scientists and astronomical researchers, anything Chinese was considered a pale imitation of the real thing, including their scientific efforts.

It may also have somehow been shunted into the realm of the unbelievable because of the involvement of Janssen's acquaintance, Jules Verne. His stature as a scientific researcher may ironically have been diminished by his fame as a science-fiction writer.

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