Astronomy Picture of the Day 12-13-03

Explanation: Only a few stars can be found within ten light-years of our lonely Sun, situated near an outer spiral arm of the Milky Way galaxy. But if the Sun were found within one of our galaxy's star clusters, thousands of stars might occupy a similar space. What would the night sky look like in such a densely packed stellar neighborhood? When Roger Hopkins took this picture at the Montezuma National Wildlife Refuge in the Finger Lakes region of western New York, USA, he was struck by this same notion. Appropriately, he had photographed a flock of starlings against the backdrop of a serene sunset. He then manipulated the image so that the black bird silhouettes were changed to white. The final picture dramatically suggests the tantalizing spectacle of approaching night in crowded skies above a cluster star world.

Ah, the wonders of Photoshop. ;-)

Sunstorm electron clouds surrounding Earth studied
UNIVERSITY OF CALIFORNIA-SAN DIEGO NEWS RELEASE
Posted: December 12, 2003

Using an orbiting camera designed to block the light from the sun and stars, an international team of solar physicists has been able for the first time to directly image clouds of electrons surrounding Earth that travel from the sun during periods of solar flare activity.

These electron clouds, a part of the solar atmosphere that extends millions of miles from the sun, cause geomagnetic storms that can disrupt communications satellites, expose high-flying aircraft to excess radiation and even damage ground-based power-generating facilities.

The images taken by this new camera, which will be discussed at a scientific session and news conference at the fall meeting in San Francisco of the American Geophysical Union, should allow space weather forecasters to substantially improve their predictions of geomagnetic storms.

"Until now, we didn't have a good way to view the clouds of electrons that pass Earth from coronal mass ejections," said Bernard V. Jackson, a solar physicist at the University of California, San Diego. "We are living inside the solar atmosphere, but up until now had no way to view it, so space forecasters couldn't be certain whether an ejection from the sun would affect the Earth one to five days later or harmlessly pass us by. Now that we can see these clouds as they travel through space outward from the sun, we can map their trajectories."

The orbiting camera, known as the Solar Mass Ejection Imager, was built by scientists and engineers at UCSD, the Air Force Research Laboratory, University of Birmingham in the United Kingdom, Boston College and Boston University. The instrument was launched in January by the Air Force and has provided the team of scientists with numerous images of coronal mass ejections, which can be seen in the images because of the faint scattering of sunlight from the clouds of electrons.

To the surprise of the scientists, the images also revealed the existence of high-altitude auroras, extending more than 500 miles above the Earth's surface. Such auroras had previously been reported by space-shuttle astronauts, but their observations were questioned because air molecules were not thought to exist in sufficient quantity at that altitude to produce such light displays.

Bright auroras seen from the surface of our planet in the high northern and southern latitudes are caused by pulses of charged particles, mostly electrons, from the sun that overload the Earth's lower radiation belt and are discharged into the atmosphere, colliding with air molecules in the atmosphere in shimmering displays of colorful light known as the northern (or southern) lights. Auroras typically extend from 60 miles above Earth's surface to several hundred miles. But at 500 miles above the Earth's surface, the density of air molecules is not enough to permit auroras-or so scientists have long believed.

"It's a mystery," said Jackson of UCSD's Center for Astrophysics and Space Sciences. "This is far higher than anyone had ever expected. It may be that nitrogen from the ionosphere is ejected into the higher altitudes during a coronal mass ejection."

The auroras were first noted by Andrew Buffington, another UCSD solar physicist, while combing through data taken by the Solar Mass Ejection Imager. In a series of image frames taken four seconds apart during a coronal mass ejection in late May, Buffington detected a bright source of light, 100 times brighter than the scattering of sunlight from the electrons. Similar sequences were seen during subsequent mass ejections by Buffington and Boston College scientists Don Mizuno and Dave Webb.

"We've observed high-altitude auroras during all of the coronal mass ejection events that engulfed Earth since the instrument became operational," says Jackson. "In fact, the last big event in late October had a lot of auroras associated with it. But we still don't understand the process that is causing them."

He said researchers at the Air Force Research Laboratory are presently studying the data to come up with some possible explanations. The project was financed by the U.S. Air Force, National Aeronautics and Space Administration, National Science Foundation and the University of Birmingham.

AP article, same stuff, I think. Wow!

High-Altitude Auroras Stump Scientists

Thu Dec 11, 3:48 AM ET

Add Science - AP to My Yahoo!

By ANDREW BRIDGES, AP Science Writer

SAN FRANCISCO - A military satellite has detected auroras, those shimmering displays of colorful light, at altitudes far higher above Earth than previously known, confirming anecdotal reports from astronauts that scientists had dismissed.

Known as the northern or southern lights, the auroras typically seen from the ground have been known to extend from about 60 miles to a few hundred miles above the planet's surface.

Now, cameras on the Air Force's Coriolis satellite launched early this year are also spotting auroras above 500 miles. How they are produced at such heights is still a mystery.

"It's a relatively new aspect of this phenomenon no one has seen at this altitude," said David Webb, a research physicist at Boston College.

Details were presented Wednesday at the fall meeting of the American Geophysical Union.

Pulses of charged particles, mostly electrons, produce auroras when they are flung off by the sun and collide with molecules in the Earth's atmosphere.

Previously, scientists believed the effect was limited to lower altitudes where the atmosphere is more dense. High above Earth, they believed, there simply weren't enough air molecules to create the effect.

As a result, astronauts' reports of seeing auroras weren't believed, said Bernard V. Jackson, a solar physicist at the University of California, San Diego.

But something is there, scientists now say, and in sufficient quantities to create the newly spotted high-altitude auroras.

One theory is that the explosions of particles from the sun eject nitrogen from the ionosphere to much higher altitudes, Webb said.

Scientists first noticed the high-altitude auroras while looking at pictures from a trio of cameras included in the $10 million Solar Mass Ejection Imager. The experimental instrument was launched in January.

In images taken during a massive solar eruption in May, scientists observed a brightening that nearly swamped the instrument's cameras.

Great question. You have stumbled upon Olbers' Paradox.

A detailed description of Olbers' paradox allows you to conclude that if the universe

(a) were big enough so that every line of sight ended in a star,

(b) were infinitely old,

(d) if several other simple assumptions were satisfied,

then the entire night sky would be roughly as bright as the surface of our sun!

Therefore, the simple observation that the night sky is dark allows us to say something very profound about our universe: it cannot be infinitely big, infinitely old and static all at the same time! Many people used to believe that the universe was this way, and it turns out that all they would have had to do to convince themselves otherwise was think carefully about a simple question that every child asks: "Why is the sky dark at night?" This is definitely an argument for the old adage that there's no such thing as a stupid question! As it turns out, we still don't know whether the universe is infinitely big (but most of us think not), but we do have a good grasp on the age of the universe and we do know that it is expanding, and of the two, it is the finite age of the universe which seems to provide the main explanation for Olbers' paradox.

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