Everyday Thinking

Milky Way only has two spiral arms, not four

For decades, astronomers have been blind to what our galaxy, the Milky Way, really looks like. After all, we sit in the midst of it and can't step outside for a bird's eye view.

Now, new images from NASA's Spitzer Space Telescope are shedding light on the true structure of the Milky Way, revealing that it has just two major arms of stars instead of the four it was previously thought to possess.

"Spitzer has provided us with a starting point for rethinking the structure of the Milky Way," said Robert Benjamin of the University of Wisconsin, Whitewater, who presented the new results at a press conference today at the 212th meeting of the American Astronomical Society in St. Louis, Mo. "We will keep revising our picture in the same way that early explorers sailing around the globe had to keep revising their maps."

Since the 1950s, astronomers have produced maps of the Milky Way. The early models were based on radio observations of gas in the galaxy, and suggested a spiral structure with four major star-forming arms, called Norma, Scutum-Centaurus, Sagittarius and Perseus. In addition to arms, there are bands of gas and dust in the central part of the galaxy. Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms.

Read the full article here.

(Image: NASA/JPL-Caltech)

Meteor shower alert!

ETA AQUARID METEOR SHOWER:  If you see a meteor flit across the sky tonight, it could be a piece of Halley's Comet. Earth is crossing a stream of dusty debris from Halley and this is causing the annual eta Aquarid meteor shower. Sky watchers in the tropics and southern hemisphere (where the shower is most intense) could see as many as 70 meteors per hour during the dark hours before dawn on Monday, May 5th, and Tuesday, May 6th.  The show is diminished at northern latitudes where rates may be 15 meteors per hour or less.  Check http://spaceweather.com for sky maps and more information.

Our local forecast calls for mostly clear skies overnight with lows in the 30s. It could be perfect for a little skywatching.

Earth's magnetic field does strange things to the moon

Behold the full Moon. Ancient craters and frozen lava seas lie motionless under an airless sky of profound quiet. It's a slow-motion world where even a human footprint may last millions of years. Nothing ever seems to happen there.

Right?

Wrong. NASA-supported scientists have realized that something does happen every month when the Moon gets a lashing from Earth's magnetic tail.

"Earth's magnetotail extends well beyond the orbit of the Moon and, once a month, the Moon orbits through it," says Tim Stubbs, a University of Maryland scientist working at the Goddard Space Flight Center. "This can have consequences ranging from lunar 'dust storms' to electrostatic discharges."

(Above: The full moon inside Earth's magnetic tail, March 2008.)

Yes, Earth does have a magnetic tail. It is an extension of the same familiar magnetic field we experience when using a Boy Scout compass. Our entire planet is enveloped in a bubble of magnetism, which springs from a molten dynamo in Earth's core. Out in space, the solar wind presses against this bubble and stretches it, creating a long "magnetotail" in the downwind direction: diagram.

Anyone can tell when the Moon is inside the magnetotail. Just look: "If the Moon is full, it is inside the magnetotail," says Stubbs. "The Moon enters the magnetotail three days before it is full and takes about six days to cross and exit on the other side."

It is during those six days that strange things can happen.

During the crossing, the Moon comes in contact with a gigantic "plasma sheet" of hot charged particles trapped in the tail. The lightest and most mobile of these particles, electrons, pepper the Moon's surface and give the Moon a negative charge.

On the Moon's dayside this effect is counteracted to a degree by sunlight: UV photons knock electrons back off the surface, keeping the build-up of charge at relatively low levels. But on the nightside, in the cold lunar dark, electrons accumulate and voltages can climb to hundreds or thousands of volts.

Walking across the dusty charged-up lunar terrain, astronauts may find themselves crackling with electricity like a sock pulled out of a hot dryer. Touching another astronaut, a doorknob, a piece of sensitive electronics—any of these simple actions could produce an unwelcome zap.

"Proper grounding is strongly recommended," advises Stubbs.

The ground, meanwhile, may leap into the sky. There is compelling evidence (see, e.g., the Surveyor 7 image below) that fine particles of moondust, when sufficiently charged-up, actually float above the lunar surface. This could create a temporary nighttime atmosphere of dust ready to blacken spacesuits, clog machinery, scratch faceplates (moondust is very abrasive) and generally make life difficult for astronauts.

(Above: In 1968, on many occasions, NASA's Surveyor 7 moon lander photographed a strange "horizon glow" after dark. Researchers now believe the glow is sunlight scattered from electrically-charged moondust floating just above the lunar surface.)

Stranger still, moondust might gather itself into a sort of diaphanous wind. Drawn by differences in global charge accumulation, floating dust would naturally fly from the strongly-negative nightside to the weakly-negative dayside. This "dust storm" effect would be strongest at the Moon's terminator, the dividing line between day and night.

Much of this is pure speculation, Stubbs cautions. No one can say for sure what happens on the Moon when the magnetotail hits, because no one has been there at the crucial time. "Apollo astronauts never landed on a full Moon and they never experienced the magnetotail."

The best direct evidence comes from NASA's Lunar Prospector spacecraft, which orbited the Moon in 1998-99 and monitored many magnetotail crossings. During some crossings, the spacecraft sensed big changes in the lunar nightside voltage, jumping "typically from -200 V to -1000 V," says Jasper Halekas of UC Berkeley who has been studying the decade-old data.

Above: In 1968, on many occasions, NASA's Surveyor 7 moon lander photographed a strange "horizon glow" after dark. Researchers now believe the glow is sunlight scattered from electrically-charged moondust floating just above the lunar surface.

"It is important to note," says Halekas, "that the plasma sheet (where all the electrons come from) is a very dynamic structure. The plasma sheet is in a constant state of motion, flapping up and down all the time. So as the Moon orbits through the magnetotail, the plasma sheet can sweep across it over and over again. Depending on how dynamic things are, we can encounter the plasma sheet many times during a single pass through the magnetotail with encounters lasting anywhere from minutes to hours or even days."

"As a result, you can imagine how dynamic the charging environment on the Moon is. The Moon can be just sitting there in a quiet region of the magnetotail and then suddenly all this hot plasma goes sweeping by causing the nightside potential to spike to a kilovolt. Then it drops back again just as quickly."

The roller coaster of charge would be at its most dizzying during solar and geomagnetic storms. "That is a very dynamic time for the plasma sheet and we need to study what happens then," he says.

What happens then? Next-generation astronauts are going to find out. NASA is returning to the Moon in the decades ahead and plans to establish an outpost for long-term lunar exploration. It turns out they'll be exploring the magnetotail, too.

(Written by Dr. Tony Phillips, Science@NASA)

The vanishing rings of Saturn

Saturn: jewel of the solar system, taker of breaths, ringed beauty. Even veteran astronomers can't help but gasp when they see her through a small telescope.

Red Alert: Saturn's rings are vanishing.

Around the world, amateur astronomers have noticed the change; Saturn's wide open rings are rapidly narrowing into a thin line. Efrain Morales Rivera sends these pictures taken through a backyard telescope in Aguadilla, Puerto Rico:

"The rings have narrowed considerably in the last year," he reports. "The Cassini division (a dark gap in the rings) is getting hard to see."

Four hundred years ago, the same phenomenon puzzled Galileo. Peering through a primitive spy glass, he discovered Saturn's rings in 1610 and immediately wrote to his Medici patrons: "I found another very strange wonder, which I should like to make known to their Highnesses…." He was dumbfounded, however, when the rings winked out little more than a year later.

What happened?

The same thing that's happening now: we're experiencing a "ring plane crossing." As Saturn goes around the sun, it periodically turns its rings edge-on to Earth—once every 14-to-15 years. Because the rings are so thin, they can actually disappear when viewed through a small telescope.

Click here to read the full article.

Extreme Weather on Venus

Venus Express has revealed a planet of extraordinarily changeable and extremely large-scale weather. Bright hazes appear in a matter of days, reaching from the south pole to the low southern latitudes and disappearing just as quickly. Such ‘global weather’, unlike anything on Earth, has given scientists a new mystery to solve.

The cloud-covered world of Venus is all but a featureless, unchangeable globe at visible wavelengths of light. Switch to the ultraviolet and it reveals a truly dynamic nature. Transient dark and bright markings stripe the planet, indicating regions where solar ultraviolet radiation is absorbed or reflected, respectively.

Venus Express watches the behaviour of the planet’s atmosphere with its Venus Monitoring Camera (VMC). It has seen some amazing things. In July 2007, VMC captured a series of images showing the development of the bright southern haze. Within days, the high-altitude veil continually brightened and dimmed, moving towards equatorial latitudes and back towards the pole again.

Such global weather suggests that fast dynamical, chemical and microphysical processes are at work on the planet. During these episodes, the brightness of the southern polar latitudes increased by about a third and faded just as quickly, as sulphuric acid particles coagulate.

Read the full article here.

Lecture: "Searching for Extraterrestrial Life" at Ithaca College

Luke Keller — an assistant professor of physics at Ithaca College and a member of a NASA team studying the formation of planetary systems — will give a presentation, “Searching for Extraterrestrial Life: Molecules, UFOs, and Little Green Men,” on Tuesday, Feb. 19. Free and open to the public, the talk will begin at 7:30 p.m. in the Emerson Suites, Phillips Hall.

“In the past decade, astronomers have identified over one hundred planets orbiting stars other than the sun,” Keller said. “What are those worlds like and is it likely that they host living organisms?”

Astronomers have also observed organic molecules in interstellar space, Keller added, and many of them orbiting young stars that are probably just now forming planetary systems. How do these systems compare to our own solar system as it was forming? Are distant planetary systems anything like our own? If intelligent life has evolved elsewhere in the galaxy, could extra-terrestrials travel between stars?

“Might they have tried to communicate with us or visit us?” Keller asked. “We can explore these questions by applying some very simple principles of physics, biology, and chemistry. Come join the discussion!”

Part of the college’s Physics Café series, Keller’s talk is also an event in the annual Winter Recess Teacher’s Festival, sponsored by the Ithaca Visitors Bureau.

The Physics Café is a campus-wide lecture series sponsored by the college’s Department of Physics. The goal is to grab and hold the attention of science and nonscience majors by offering talks on exciting and accessible current topics in physics. Past Café lectures have featured the time-warping properties of black holes, the communication abilities of elephants, remote sensing of archaeological sites, and string theory. Informal talk-back sessions with the speaker follow the presentation.

For more information on the series, contact Beth Ellen Clark Joseph, associate professor of physics, at bclark@ithaca.edu or (607) 274 3968.

Touching the Invisible Sky

Images from NASA telescopes are jewels of the space program, marvelous to behold. But how do you behold them when you can't see?

The answer lies between the covers of a new NASA-funded book written in Braille, Touch the Invisible Sky.

In a forward to the volume, blind mountain climber Erik Weihenmayer writes, "Sight ... is only one of the many tools with which to experience the marvels of the world." Touch the Invisible Sky uses Braille, large type print, and tactile diagrams of celestial images observed by space telescopes Hubble, Chandra, and Spitzer to reveal the cosmos to the blind and seeing-impaired.

Many of the pictures in the book show the cosmos at wavelengths that no human eye can see--e.g., infra-red, ultraviolet and x-rays. "By showing these images, we remind readers that most of the universe and its beauty is hidden for all of our eyes unless we use special telescopes," says Doris Daou, a NASA astronomer who co-authored the book along with Noreen Grice and Simon Steele.

According to Kathleen Lestition, who coordinates Education and Outreach for the Chandra X-ray Center, "The Touch the Invisible Sky project began as a small mission grant, but NASA is making this book a national resource, distributing copies of the book at no cost to schools of the blind around the US, the Library of Congress, several blind technology and training centers, and state libraries that have astronomy collections."

Science@NASA asked two blind readers to review the book. Until age 15, Tim Hendel could see light and dark, colors, shadows, and large objects such as the sun and moon. He could not read print but learned to read Braille. Deborah Saylor was born totally blind and also reads Braille. Hendel and Saylor live in Huntsville, Alabama, and have been space enthusiasts since childhood. Both experienced Touch the Invisible Sky and shared their comments.

Tim Hendel:

"Even though I've lived in Huntsville, which is nicknamed the 'Rocket City,' for twelve years, I had no idea what a space telescope looked like or how a star might be depicted on a map. There's not much information on this kind of thing in Braille, so I was thrilled to read Touch the Invisible Sky.

On page 4 is a depiction of all the wavelengths of the electro-magnetic spectrum, from radio to gamma-rays. It shows, in a way, that all humans are partially blind. No one can see gamma-rays! Yet the cosmos is bright and lively in these 'invisible' wavelengths.

I'm a ham radio operator, so I already had a good understanding of the radio part of the spectrum, but it's useful to see the entire spectrum shown on one diagram. I can show this diagram to some of my other blind friends to explain how the whole spectrum comes together and how astronomers use different kinds of telescopes to 'see' everything from radio waves to gamma-rays.

I knew that our sun emits light and heat, and I had a vague notion that there were other kinds of radiation that our sun and other stars emit. But looking at the diagrams in the book brought home to me just how little of the actual energy sent out by stars can be seen with the eyes or felt on the skin."

Deborah Saylor:

"I moved to Huntsville a few years ago. After all these years of living here in the Rocket City and hearing about the space industry, I'm finally able to appreciate space exploration in the same way everyone else does! So I am, to say the least, very excited about being able to see this book!

The thing that impressed me so much about Touch the Invisible Sky was the way the authors put things together so I could experience what people with sight are seeing. The diagrams helped me to see, but, through touch. The explanations of the diagrams were very helpful for getting the ideas across.

I like this book a lot, and I recommend it to others. It's really something!"

Touch the Invisible Sky ends with the following analogy: "Imagine that you could only hear sound from the middle three keys on a piano and were asked to name a song.... Being able to study a star, nebula, or galaxy across the entire electromagnetic spectrum gives us the big picture, providing clues to unravel the greatest mysteries ...."

Saylor, a Van Cliburn finalist who plays entire piano concertos from memory, agrees: "The way to seek and learn the most is to develop as many ways of 'seeing' things as possible. And keep your sense of curiosity and wonder alive, always!"

That's exactly what scientists do as they journey through the cosmos, and now the blind can ride along.

(Story by Dauna Coulter; credit: Science@NASA)

Solar System's History Found In Grain Of Dust

Four years ago, NASA's Stardust spacecraft chased down a comet and collected grains of dust blowing off its nucleus. When the spacecraft Comet Wild-2 returned, comet dust was shipped to scientists all over the world, including University of Minnesota physics professor Bob Pepin. After testing helium and neon trapped in the dust specks, Pepin and his colleagues report that while the comet formed in the icy fringes of the solar system, the dust appears to have been born close to the infant sun and bombarded by intense radiation from these and other gases before being flung out beyond Neptune and trapped in the comet.

The finding opens the question of what was going on in the early life of the solar system to subject the dust to such intense radiation and hurl them hundreds of millions of miles from their birthplace.

The studies of cometary dust are part of a larger effort to trace the history of our celestial neighborhood.

"We want to establish what the solar system looked like in the very early stages," said Pepin. "If we establish the starting conditions, we can tell what happened in between then and now." One early event was the birth of Earth's moon, about 50 million years after the solar system formed.

Read the full article here.

(Image: Comet Wild 2, credit NASA)

The little rovers that could

Inch by power-conserving inch, drivers on Earth have moved the Mars rover Spirit to a spot where it has its best chance at surviving a third Martian winter -- and where it will celebrate its fourth anniversary (in Earth years) since bouncing down on Mars for a projected 90-day mission in January 2004.

Meanwhile, researchers are considering the implications of what Cornell's Steve Squyres, principal investigator for NASA's Mars Exploration Rover mission, calls "one of the most significant" mission discoveries to date: silica-rich deposits uncovered in May by Spirit's lame front wheel that provide new evidence for a once-habitable environment in Gusev Crater.

Read the full article here.

(Image courtesy of  NASA/JPL-Caltech)

NASA tests inflatable moon houses

NASA is thinking about what kind of moon base it wants to build. One option: inflatable houses. Banish thoughts of bouncy-bounces or pool toys from your mind. A high-tech inflatable building will be tested in the extreme environment of Antarctica starting in January.

Listen to the story originally aired on Weekend Edition.