Posted on by Fraser Cain

Big Galaxies, Older Stars

Galaxy cluster Abell 3266. Image credit: NOAO Click to enlarge
A comprehensive survey of more than 4,000 elliptical and lenticular galaxies in 93 nearby galaxy clusters has found a curious case of galactic ?downsizing.?

Contrary to expectations, the largest, brightest galaxies in the census consist almost exclusively of very old stars, with much of their stellar populations having formed as long ago as 13 billion years. There appears to be very little recent star formation in these galaxies, nor is there strong evidence for recent ingestion of smaller, younger galaxies.

By contrast, the smaller, fainter galaxies studied by the NOAO Fundamental Plane Survey are significantly younger?their stars were formed as little as four billion years ago, according to new results from the survey team to be published in the September 10, 2005, Astrophysical Journal.

These findings are based on a sample more than five times larger than previous efforts. The results of the survey contrast sharply with conventional hierarchical model of galaxy formation and evolution, where large elliptical galaxies in the nearby universe formed by swallowing smaller galaxies with young stars; this theory predicts that, on average, the stars in the largest elliptical galaxies should be no older than those in the smallest ones.

?This sample probes the largest and richest galaxy clusters in the nearby universe, out to a distance of about a billion light-years from Earth,? says Jenica Nelan, lead author of the study. ?Our analysis shows that there is a clear relationship between mass and age in these red galaxies, meaning that the stars in the biggest, oldest galaxies that we studied formed early in the history of the Universe. On average, the smaller galaxies have one-tenth the mass of the larger ones, and are only about half their age.?

?The term ?downsizing? essentially means that when the Universe was young, the star formation activity occurred in large galaxies, but as the Universe aged, the ?action? stopped in the larger galaxies, even as it continued in smaller galaxies,? says Michael Hudson of the University of Waterloo, Ontario, Canada, principal investigator for the NOAO Fundamental Plane Survey.

The new study is based on thousands of spectra obtained by the Fundamental Plane Survey team over dozens of nights at the WIYN 3.5-meter telescope at Kitt Peak National Observatory, southwest of Tucson, AZ, and the National Science Foundation?s Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, east of La Serena, Chile. With some painstaking work, these spectra can reveal the average age of the stars that make up a galaxy.

?Although we cannot directly see these galaxies as they were in the past, their stars are a kind of ?fossil record? that can be used to unearth their histories,? Hudson explains. ?It appears that the older galaxies are much less of a ?melting pot? than had been thought, and that their star formation activity turned off somehow while they were being put together.?

The evolutionary history of elliptical galaxies and lenticular galaxies (which have a central bulge and a disk, but no evidence of spiral arms) is not well understood. Their colors appear to be ?redder? than typical spiral galaxies. The largest ellipticals are the reddest of all, but until this work it has not been clear whether this property results primarily from being older in age, as the survey found, or from having a higher proportion of heavy chemical elements (metallicity content).

?These so-called red galaxies contain the bulk of the stellar mass in the nearby universe, but we know little about their formation and evolution,? says co-author Russell Smith of the University of Waterloo. ?It was thought that all of the red galaxies were made of stars that formed very early, and are now quite old. Our results show that while this is true for the large galaxies, the smaller ones formed their stars comparatively recently in the history of the Universe. We predict that as new surveys look deeper and hence further into the past, they should see fewer faint red galaxies?

An image of galaxy cluster Abell 3266 taken by survey team members at the Gemini South telescope as part of their follow-up work is available above.

Lead author Jenica Nelan completed this work while earning her doctorate at Dartmouth College; she is now an astronomer at Yale University.

Co-authors of this paper include Hudson and Smith of the University of Waterloo; Gary Wegner of Dartmouth College; John R. Lucey, Stephen A. W. Moore, and Stephen J. Quinney of the University of Durham, and Nicholas B. Suntzeff of NOAO?s Cerro Tololo Inter-American Observatory.

The Fundamental Plane Survey is one of 18 projects granted long-term access to observing nights at the telescope of the National Optical Astronomy Observatory (NOAO) under the NOAO Survey Program.

See here for more information:
www.noao.edu/gateway/surveys/programs.html and astro.uwaterloo.ca/~mjhudson/nfp

Original Source: NOAO News Release

Posted on by Fraser Cain

Cracked Features on Enceladus Are Very Young

Infrared mapping spectrometer image of Enceladus. Image credit: NASA/JPL/University of Arizona Click to enlarge
The Cassini spacecraft has discovered the long, cracked features dubbed “tiger stripes” on Saturn’s icy moon Enceladus are very young — between 10 and 1,000 years young.

These findings support previous results showing the moon’s southern pole is active. The pole had episodes of geologic activity as recently as 10 years ago. These cracked features are approximately 130 kilometers long (80 miles), spaced about 40 kilometers (25 miles) apart and run roughly parallel to one another.

The cracks act like vents. They spew vapor and fine ice water particles that have become ice crystals. This crystallization process can be dated, which helped scientists pin down the age of the features.

“There appears to be a continual supply of fresh, crystalline ice at the tiger stripes, which could have been very recently resurfaced,” said Dr. Bonnie Buratti. She is a team member of the Cassini visual and infrared mapping spectrometer at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Enceladus is constantly evolving and getting a makeover.”

This finding is especially exciting because ground-based observers have seen tiny Enceladus brighten as its south pole was visible from Earth. Cassini allows scientists to see close up that the brightening is caused by geologic activity. When NASA’s Voyager 2 spacecraft flew over the moon’s north pole in 1981, it did not observe the tiger stripes.

Cassini’s visual and infrared mapping spectrometer shows water ice exists in two forms on Enceladus: in pristine, crystalline ice and radiation-damaged amorphous ice.

When ice comes out of the “hot” cracks, or “tiger stripes,” at the south pole, it forms as fresh, crystalline ice. As the ice near the poles remains cold and undisturbed, it ages and converts to amorphous ice. Since this process is believed to take place over decades or less, the tiger stripes must be very young.

“One of the most fascinating aspects of Enceladus is that it is so very small as icy moons go, but so very geophysically active. It’s hard for a body as small as Enceladus to hold onto the heat necessary to drive such large-scale geophysical phenomena, but it has done just that,” said Dr. Bob Brown. Brown is a team leader for the visual and infrared mapping spectrometer at the University of Arizona, Tucson. “Enceladus and its incredible geology is a marvelous puzzle for us to figure out.”

Adding to the already mounting evidence for an active body is the correlation of results from multiple instruments. Cassini’s cameras provided detailed images of the south polar cap, in which the tiger stripe fractures were found to be among the hottest features.

The timing of the craft’s ion and neutral mass spectrometer and the cosmic dust analyzer observations seems to indicate the vapor and fine material are originating from the “hot” polar cap region. These data also indicate the production of water vapor and ejection of fine material are connected, as they are in a comet. This suggests that vapor and dust-sized icy material are coming from the tiger stripes.

Enceladus is on a short list of bodies in our solar system where scientists have found internal activity. The others are the volcanoes on Jupiter’s moon Io and geysers on Neptune’s moon Triton.

Data for these measurements were taken during Cassini’s closest flyby on July 14, 2005. The spacecraft came within 175 kilometers (109 miles) of the surface of Enceladus. Enceladus is 500 kilometers (314 miles) across and has the most reflective surface in the solar system.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington.

For information about the Cassini-Huygens mission on the Web, visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov . For information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/index.html .

Original Source: NASA News Release

Posted on by Fraser Cain

Will the Universe Expand Forever?

The SuperNova/Acceleration Probe, SNAP. Image credit: Berkeley Lab Click to enlarge
What is the mysterious dark energy that’s causing the expansion of the universe to accelerate? Is it some form of Einstein’s famous cosmological constant, or is it an exotic repulsive force, dubbed “quintessence,” that could make up as much as three-quarters of the cosmos? Scientists from Lawrence Berkeley National Laboratory (Berkeley Lab) and Dartmouth College believe there is a way to find out.

In a paper to be published in Physical Review Letters, physicists Eric Linder of Berkeley Lab and Robert Caldwell of Dartmouth show that physics models of dark energy can be separated into distinct scenarios, which could be used to rule out Einstein’s cosmological constant and explain the nature of dark energy. What’s more, scientists should be able to determine which of these scenarios is correct with the experiments being planned for the Joint Dark Energy Mission (JDEM) that has been proposed by NASA and the U.S. Department of Energy.

“Scientists have been arguing the question ‘how precisely do we need to measure dark energy in order to know what it is?'” says Linder. “What we have done in our paper is suggest precision limits for the measurements. Fortunately, these limits should be within the range of the JDEM experiments.”

Linder and Caldwell are both members of the DOE-NASA science definition team for JDEM, which has the responsibility for drawing up the mission’s scientific requirements. Linder is the leader of the theory group for SNAP ? the SuperNova/Acceleration Probe, one of the proposed vehicles for carrying out the JDEM mission. Caldwell, a professor of physics and astronomy at Dartmouth, is one of the originators of the quintessence concept.

In their paper in Physical Review Letters Linder and Caldwell describe two scenarios, one they call “thawing” and one they call “freezing,” which point toward distinctly different fates for our permanently expanding universe. Under the thawing scenario, the acceleration of the expansion will gradually decrease and eventually come to a stop, like a car when the driver eases up on the gas pedal. Expansion may continue more slowly, or the universe may even recollapse. Under the freezing scenario, acceleration continues indefinitely, like a car with the gas pedal pushed to the floor. The universe would become increasingly diffuse, until eventually our galaxy would find itself alone in space.

Either of these two scenarios rules out Einstein’s cosmological constant. In their paper Linder and Caldwell show, for the first time, how to cleanly separate Einstein’s idea from other possibilities. Under any scenario, however, dark energy is a force that must be reckoned with.

Says Linder, “Because dark energy makes up about 70 percent of the content of the universe, it dominates over the matter content. That means dark energy will govern expansion and, ultimately, determine the fate of the universe.”

In 1998, two research groups rocked the field of cosmology with their independent announcements that the expansion of the universe is accelerating. By measuring the redshift of light from Type Ia supernovae, deep-space stars that explode with a characteristic energy, teams from the Supernova Cosmology Project headquartered at Berkeley Lab and the High-Z Supernova Search Team centered in Australia determined that the expansion of the universe is actually accelerating, not decelerating. The unknown force behind this accelerated expansion was given the name “dark energy.”

Prior to the discovery of dark energy, conventional scientific wisdom held that the Big Bang had resulted in an expansion of the universe that would gradually be slowed down by gravity. If the matter content in the universe provided enough gravity, one day the expansion would stop altogether and the universe would fall back on itself in a Big Crunch. If the gravity from matter was insufficient to completely stop the expansion, the universe would continue floating apart forever.

“From the announcements in 1998 and subsequent measurements, we now know that the accelerated expansion of the universe did not start until sometime in the last 10 billion years,” Caldwell says.

Cosmologists are now scrambling to determine what exactly dark energy is. In 1917 Einstein amended his General Theory of Relativity with a cosmological constant, which, if the value was right, would allow the universe to exist in a perfectly balanced, static state. Although history’s most famous physicist would later call the addition of this constant his “greatest blunder,” the discovery of dark energy has revived the idea.

“The cosmological constant was a vacuum energy (the energy of empty space) that kept gravity from pulling the universe in on itself,” says Linder. “A problem with the cosmological constant is that it is constant, with the same energy density, pressure, and equation of state over time. Dark energy, however, had to be negligible in the universe’s earliest stages; otherwise the galaxies and all their stars would never have formed.”

For Einstein’s cosmological constant to result in the universe we see today, the energy scale would have to be many orders of magnitude smaller than anything else in the universe. While this may be possible, Linder says, it does not seem likely. Enter the concept of “quintessence,” named after the fifth element of the ancient Greeks, in addition to air, earth, fire, and water; they believed it to be the force that held the moon and stars in place.

“Quintessence is a dynamic, time-evolving, and spatially dependent form of energy with negative pressure sufficient to drive the accelerating expansion,” says Caldwell. “Whereas the cosmological constant is a very specific form of energy ? vacuum energy ? quintessence encompasses a wide class of possibilities.”

To limit the possibilities for quintessence and provide firm targets for basic tests that would also confirm its candidacy as the source of dark energy, Linder and Caldwell used a scalar field as their model. A scalar field possesses a measure of value but not direction for all points in space. With this approach, the authors were able to show quintessence as a scalar field relaxing its potential energy down to a minimum value. Think of a set of springs under tension and exerting a negative pressure that counteracts the positive pressure of gravity.

“A quintessence scalar field is like a field of springs covering every point in space, with each spring stretched to a different length,” Linder said. “For Einstein’s cosmological constant, each spring would be the same length and motionless.”

Under their thawing scenario, the potential energy of the quintessence field was “frozen” in place until the decreasing material density of an expanding universe gradually released it. In the freezing scenario, the quintessence field has been rolling towards its minimum potential since the universe underwent inflation, but as it comes to dominate the universe it gradually becomes a constant value.

The SNAP proposal is in research and development by physicists, astronomers, and engineers at Berkeley Lab, in collaboration with colleagues from the University of California at Berkeley and many other institutions; it calls for a three-mirror, 2-meter reflecting telescope in deep-space orbit that would be used to find and measure thousands of Type Ia supernovae each year. These measurements should provide enough information to clearly point towards either the thawing or freezing scenario ? or to something else entirely new and unknown.

Says Linder, “If the results from measurements such as those that could be made with SNAP lie outside the thawing or freezing scenarios, then we may have to look beyond quintessence, perhaps to even more exotic physics, such as a modification of Einstein’s General Theory of Relativity to explain dark energy.”

Original Source: Berkeley Lab News Release

Posted on by Fraser Cain

Enceladus Compared to the United Kingdom

Saturn’s moon Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
Saturn’s moon Enceladus is only 505 kilometers (314 miles) across, small enough to fit within the length of the United Kingdom, as illustrated here. The intriguing icy moon also could fit comfortably within the states of Arizona or Colorado.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Asteroid Dust Could Influence the Weather

The asteroid’s dust trail. Image credit: Sandia National Laboratories. Click to enlarge
Dust from asteroids entering the atmosphere may influence Earth?s weather more than previously believed, researchers have found.

In a study to be published this week in the journal Nature, scientists from the Australian Antarctic Division, the University of Western Ontario, the Aerospace Corporation, and Sandia and Los Alamos national laboratories found evidence that dust from an asteroid burning up as it descended through Earth?s atmosphere formed a cloud of micron-sized particles significant enough to influence local weather in Antarctica.

Micron-sized particles are big enough to reflect sunlight, cause local cooling, and play a major role in cloud formation, the Nature brief observes. Longer research papers being prepared from the same data for other journals are expected to discuss possible negative effects on the planet?s ozone layer.

?Our observations suggest that [meteors exploding] in Earth?s atmosphere could play a more important role in climate than previously recognized,? the researchers write.

Scientists had formerly paid little attention to asteroid dust, assuming that the burnt matter disintegrated into nanometer-sized particles that did not affect Earth?s environment. Some researchers (and science fiction writers) were more interested in the damage that could be caused by the intact portion of a large asteroid striking Earth.

But the size of an asteroid entering Earth?s atmosphere is significantly reduced by the fireball caused by the friction of its passage. The mass turned to dust may be as much as 90 to 99 percent of the original asteroid. Where does this dust go?

The uniquely well-observed descent of a particular asteroid and its resultant dust cloud gave an unexpected answer.

On Sept. 3, 2004, the space-based infrared sensors of the U.S. Department of Defense detected an asteroid a little less than 10 meters across, at an altitude of 75 kilometers, descending off the coast of Antarctica. U.S. Department of Energy visible-light sensors built by Sandia National Laboratories, a National Nuclear Security Administration lab, also detected the intruder when it became a fireball at approximately 56 kilometers above Earth. Five infrasound stations, built to detect nuclear explosions anywhere in the world, registered acoustic waves from the speeding asteroid that were analyzed by LANL researcher Doug ReVelle. NASA?s multispectral polar orbiting sensor then picked up the debris cloud formed by the disintegrating space rock.

Some 7.5 hours after the initial observation, a cloud of anomalous material was detected in the upper stratosphere over Davis Station in Antarctica by ground-based lidar.

?We noticed something unusual in the data,? says Andrew Klekociuk, a research scientist at the Australian Antarctic division. ?We?d never seen anything like this before ? [a cloud that] sits vertically and things blow through it. It had a wispy nature, with thin layers separated by a few kilometers. Clouds are more consistent and last longer. This one blew through in about an hour.?

The cloud was too high for ordinary water-bearing clouds (32 kilometers instead of 20 km) and too warm to consist of known manmade pollutants (55 degrees warmer than the highest expected frost point of human-released solid cloud constituents). It could have been dust from a solid rocket launch, but the asteroid?s descent and the progress of its resultant cloud had been too well observed and charted; the pedigree, so to speak, of the cloud was clear.

Computer simulations agreed with sensor data that the particles? mass, shape, and behavior identified them as meteorite constituents roughly 10 to 20 microns in size.

Says Dee Pack of Aerospace Corporation, ?This asteroid deposited 1,000 metric tons in the stratosphere in a few seconds, a sizable perturbation.? Every year, he says, 50 to 60 meter-sized asteroids hit Earth.

Peter Brown at the University of Western Ontario, who was initially contacted by Klekociuk, helped analyze data and did theoretical modeling. He points out that climate modelers might have to extrapolate from this one event to its larger implications. ?[Asteroid dust could be modeled as] the equivalent of volcanic eruptions of dust, with atmospheric deposition from above rather than below.? The new information on micron-sized particles ?have much greater implications for [extraterrestrial visitors] like Tunguska,? a reference to an asteroid or comet that exploded 8 km above the Stony Tunguska river in Siberia in 1908. About 2150 square kilometers were devastated, but little formal analysis was done on the atmospheric effect of the dust that must have been deposited in the atmosphere.

The Sandia sensors? primary function is to observe nuclear explosions anywhere on Earth. Their evolution to include meteor fireball observations came when Sandia researcher Dick Spalding recognized that ground-based processing of data might be modified to record the relatively slower flashes due to asteroids and meteoroids. Sandia computer programmer Joe Chavez wrote the program that filtered out signal noise caused by variations in sunlight, satellite rotation, and changes in cloud cover to realize the additional capability. The Sandia data constituted a basis for the energy and mass estimate of the asteroid, says Spalding.

The capabilities of defense-related sensors to distinguish between the explosion of a nuclear bomb and the entry into the atmosphere of an asteroid that releases similar amounts of energy ? in this case, about 13 kilotons ? could provide an additional margin of world safety. Without that information, a country that experienced a high-energy asteroid burst that penetrated the atmosphere might provoke a military response by leaders who are under the false impression that a nuclear attack is underway, or lead other countries to assume a nuclear test has occurred.

Original Source: Sandia National Labs

Posted on by Fraser Cain

South Ozone Hole Returns

Ozone forecast for 1 September. Image credit: KNMI/ESA Click to enlarge
This season’s Antarctic ozone hole has swollen to an area of ten million square kilometres from mid-August – approximately the same size as Europe and still expanding. It is expected to reach maximum extent during September, and ESA satellites are vital for monitoring its development.

This year’s hole is large for this time of year, based on results from the last decade: only the ozone holes of 1996 and 2000 had a larger area at this point in their development.

Envisat’s Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) routinely monitors ozone levels on a global basis, continuing a dataset of measurements stretching back to mid-1995, previously made by the Global Ozone Monitoring Experiment (GOME) aboard the earlier ESA spacecraft ERS-2.

ESA data form the basis of an operational near-real time ozone monitoring and forecasting service forming part of the PROMOTE (PROtocol MOniToring for the GMES Service Element) consortium, made up of more than 30 partners from 11 countries, including the Royal Dutch Meteorological Institute (KNMI).

As part of the PROMOTE service, the satellite results are combined with meteorological data and wind field models so that robust ozone and ultraviolet forecasts can be made. In a first for ESA, these results are being used by the World Meteorological Organisation (WMO) to compile their regularly-updated Antarctic Ozone Bulletin.

The precise time and range of Antarctic ozone hole occurrences are determined by regional meteorological variations. During the southern hemisphere winter, the atmospheric mass above the Antarctic continent is kept cut off from exchanges with mid-latitude air by prevailing winds known as the polar vortex. This leads to very low temperatures, and in the cold and continuous darkness of this season, polar stratospheric clouds are formed that contain chlorine.

The stratospheric ozone layer that protects life on Earth from harmful ultraviolet (UV) radiation is vulnerable to the presence of certain chemicals in the atmosphere such as chlorine, originating from man-made pollutants like chlorofluorocarbons (CFCs).

Now banned under the Montreal Protocol, CFCs were once widely used in aerosol cans and refrigerators. CFCs themselves are inert, but ultraviolet radiation high in the atmosphere breaks them down into their constituent parts, which can be highly reactive with ozone.

As the polar spring arrives, the combination of returning sunlight and the presence of polar stratospheric clouds leads to splitting of chlorine into highly ozone-reactive radicals that break ozone down into individual oxygen molecules. A single molecule of chlorine has the potential to break down thousands of molecules of ozone.

The PROMOTE atmospheric ozone forecast seen here has atmospheric ozone measured in Dobson Units (DUs), which stands for the total thickness of ozone in a given vertical column if it were concentrated into a single slab at standard temperature and atmospheric pressure ? 400 DUs is equivalent to a thickness of four millimetres, for example.

Developing out of the successful precursor Tropospheric Emission Monitoring Information Service (TEMIS), PROMOTE is a portfolio of information services covering the atmosphere part of the Earth System, operating as part of ESA’s initial Services Element of Global Monitoring for Environment and Security (GMES). This is a joint initiative between ESA and the European Commission to combine all available ground- and space-based information sources and develop a global environmental monitoring capability for Europe.

Original Source: ESA Portal

Posted on by Fraser Cain

What’s Up This Week – August 29 – September 4, 2005

M17. Image credit: Hillary Mathis, N.A. Sharp, REU program/NOAO/AURA/NSF. Click to enlarge.
Monday, August 29 – Let’s begin our week by looking at a pair of planets that are moving apart. Just before dawn, have a look at how far Mercury and Saturn have now separated. In one week’s time they have drawn about how far apart as Jupiter and Venus were on the 22nd. Now, let’s wait until sunset as we see that Jupiter and Venus have now moved within 3 degrees of each other. The bright pair of planets make for a wonderful photographic opportunity, and tomorrow they will be much closer!

Tonight let’s celebrate dark skies by aiming our binoculars and telescopes about a fist’s width north of the top of the teapot’s lid – Kaus Borealis. The object of our interest tonight has many names, but let’s start by calling it M17.

Discovered twice within months in 1764 – first by Swiss astronomer de Cheseaux and then Charles Messier – this bright nebula is often referred to as the “Omega”, or “Swan” nebula. This huge area of nebulosity will appear almost like a comet in binoculars and take on the shape of the figure “2” for small telescopes. Upon closer scrutiny with larger aperture, the viewer will note the area inside the curve could possibly contain obscuring dark dust. At a dark sky location, or with the application of a filter, you can see many long filaments that radiate out from the central structure. Unlike previous study M8, the M17 does not contain any type of star cluster, although you can see many of them glittering in the folds of nebula. It is estimated that perhaps only 35 of these stars are actually associated with the “Swan” and the illuminating stars appear to be hidden within the brighter portions of the nebula itself. While estimates in distance are unclear, it is believed the M17 is about 5,700 light years from our own galaxy. It’s awesome!

Tuesday, August 30 – For a very large portion of the United States and Mexico, you will have the opportunity to watch the Moon occult bright star Upsilon Geminorum in the early morning hours. Please check this IOTA webpage for details on times and locations in your area. Clear skies!

If you were clouded out at sunset last night, look again at the western horizon as Venus and Jupiter have moved to just 2.2 degrees apart. Take a picture. Tomorrow they will be even closer.

Don’t put away your binoculars just because you think this next study is beyond you… Just lift your sights three degrees higher than the “Omega” and tonight we’ll fly with the “Eagle”.

Small binoculars will have no trouble distinguishing the cluster of stars discovered by de Cheseaux in 1746, but larger binoculars and small telescopes from a dark sky site will also see a faint nebulosity to the region that was reported by Messier in 1764. This “faint light” will remind you highly of the reflection that is seen within the Pleiades, or “Rosette” nebula. While the most outstanding views of the “Eagle” nebula are in photographs, larger telescopes will have no problem picking out a vague cloud of nebula, encased stars and an unusual dark obscuration in the center which has always reminded this author as a “Klingon Bird of Prey”. While all of this is very grand, what’s really interesting is the little notch on the northeast edge of the nebula. This is easily seen under good conditions with scopes as small as 8″ and is undeniable in larger aperture. This tiny “notch” rocketed to worldwide fame when viewed through the eyes of the Hubble. It’s name? “The Pillars of Creation”.

Wednesday, August 31 – Tonight at sunset, return again to the western horizon to have a look at our bright planetary pairing. Just 24 hours before their closest approach, you will see brilliant Venus only one and a half degrees below the Mighty Jove. This is a picture-perfect moment of our solar system’s orbits, so be sure to watch and tomorrow night brings this pair even nearer together.

Tonight will be the peak of the Andromedid meteor shower. With the Moon in our favour and the constellation of Cassiopeia already risen, let’s take a break from our studies and watch the show. For those of you in the northern hemisphere, look for the lazy “W” of Cassiopeia to the northeast. This is the radiant – or relative point of origin – for this meteor stream. At times, this shower has been known to be spectacular, but let’s stick with an accepted fall rate of around 20 per hour. These are the offspring of Beila’s Comet and have a reputation for red fireballs with spectacular trains. Happy “trails” to you!

Thursday, September 1 – In 1859, solar physicist – Richard Carrington, who originally assigned sunspot rotation numbers – observed the first solar flare ever recorded. Naturally enough, an intense aurora followed the next day. 120 years later in 1979, Pioneer 11 makes history as it flies by the Saturn. We often take our progress in space for granted, but look at how much has been achieved in just our lifetimes. A great many of us were born well before space exploration started, and quite a few of us well remember 1979. As we tip our hats toward Saturn this morning, realize in just a short period of 25 years that we have gone from just flying past Saturn to actually having landed on one of its moons.

This is it. Mark your calendars for today and take your family out to view the visually most striking planetary pairing of the year! On the western horizon just after sunset, Venus and Jupiter will have now moved to just slightly over one degree apart. Don’t miss your opportunity to photograph or witness this stunning event!

Tonight we are going to take a journey once again toward an area which has intrigued this author since I first laid eyes on it with a telescope. Some think it difficult to find, but there is a very simple trick. Look for the primary stars of Sagitta just to the west of bright Albireo. Make note of the distance between the two brightest and look exactly that distance north of the “tip of the arrow” and you’ll find the M27.

Discovered in 1764 by Messier in a three and a half foot telescope, I discovered this 48,000 year old planetary nebula for the first time in a 4.5″ telescope. I was hooked immediately. Here before my eager eyes was a glowing green “apple core” which had a quality about it that I did not understand. It somehow moved… It pulsated. It appeared “living”.

For many years I quested to understand the 850 light year distant M27, but no one could answer my questions. I researched and learned it was made up of doubly ionized oxygen. I had hoped that perhaps there was a spectral reason to what I viewed year after year – but still no answer. Like all amateurs, I became the victim of “aperture fever” and I continued to study the M27 with a 12.5″ telescope, never realizing the answer was right there – I just hadn’t powered up enough.

Several years later while studying at the Observatory, I was viewing through a friend’s identical 12.5″ telescope and as chance would have it, he was using about twice the magnification that I normally used on the “Dumbbell”. Imagine my total astonishment as I realized for the very first time that the faint central star had an even fainter companion that made it seem to wink! At smaller apertures or low power, this was not revealed. Still, the eye could “see” a movement within the nebula – the central, radiating star and its companion.

Do not sell the “Dumbbell” short. It can be seen as a small, unresolved area in common binoculars, easily picked out with larger binoculars as an irregular planetary nebula, and turns astounding with even the smallest of telescopes. In the words of Burnham, “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth…”

Friday, September 2 – If you were clouded out last night, don’t worry. Both Venus and Jupiter are still making an awesome appearance on the western sunset horizon. Now separated by about a degree and a half, watch in the days ahead as the planets once again begin to distance themselves and slowly head away towards the Sun.

When skies are dark, it’s time for us to head directly between the two lower stars in the constellations of Lyra and grab the “Ring”.

First discovered by French astronomer, Antoine Darquier in 1779, the “Ring” was cataloged later that year by Charles Messier as the M57. In binoculars the “Ring” will appear as slightly larger than a star, yet it cannot be focused to a sharp point. To a modest telescope at even low power, the M57 turns into a glowing donut against a wonderfully stellar backdrop. The average accepted distance to this unusual structure is believed to be around 1,400 light years and how you see the “Ring” on any given night is highly attributable to conditions. As aperture and power increase, so do details and it is not impossible to see braiding in the nebula structure with scopes as small as eight inches on a fine night, or to pick up the star caught on the edge in even smaller apertures.

Like all planetary nebula, seeing the central star is considered the ultimate of viewing. The central itself is a peculiar bluish dwarf which gives off a continuous spectrum and might very well be a variable. At times, this shy, near 15th magnitude star can be seen with ease with a 12.5″ telescope, yet be elusive to 31″ in aperture weeks later. No matter what details you may see, reach for the “Ring” tonight. You’ll be glad you did.

Saturday, September 3 – Tonight is New Moon and a great opportunity to have another look at all the things we’ve studied this week. However, I would encourage those of you with larger binoculars and telescopes to head for a dark sky location, because tonight we are going on a quest…

The quest for the holy “Veil”.

By no means is the Veil Nebula Complex an easy one. The brightest portion, NGC 6992, can be spotted in large binoculars and you can find it just slightly south of a central point between Epsilon and Zeta Cygnii. The NGC 6992 is much better in a 6-8″ scope however, and low power is essential to see the long ghostly filaments which span more than a degree of sky. About two and a half degrees west/southwest, and incorporating star 52 is another long narrow ribbon of what may be classified as a supernova remnant. When aperture reaches the 12″ range, so does the true breadth of this fascinating complex. It is possible to trace these long filaments across several fields of view. They sometimes dim and at other times widen, but like a surreal solar flare, you will not be able to tear your eyes away from this area. Another undesignated area lies between the two NGCs, and the whole 1,500 light year distant area spans over two and a half degrees. Sometimes known as the “Cygnus Loop”, it’s definitely one of the summer’s finest objects.

If you’re out after midnight, be sure to have a look at growing Mars. In 1976, the Viking 2 lander touched down on Mars – about 7 weeks after Viking 1. Both Spirit and Opportunity are still going strong, so don’t miss out on this year’s adventures to the Red Planet.

Sunday, September 4 – No luck at spotting Mercury just before dawn? Then grab your binoculars this morning and look bright Regulus on the horizon. You’ll find the speedy inner planet about one degree to Regulus’ north.

Skies will still be very dark tonight, Of course, studying some of the summer’s finest means that we’d be very remiss if we didn’t look at another cosmic curiosity – “The Blinking Planetary”.

Located a couple of degrees east of visible star Theta Cygnii, and in the same lower power field as 16 Cygnii, the NGC 6826 is often referred to as the “Blinking Planetary” nebula. Viewable in even small telescopes at mid to high power, you’ll learn very quickly how it came about its name. When you look directly at it, you can only see the central 9th magnitude star. Now, look away. Focus your attention on visual double 16 Cygnii. See that? When you avert, the nebula itself is visible. This is actually a trick of the eye. The central portion of our vision is more sensitive to detail and will only see the central star. At the edge of our vision, we are more likely to see dim light, and the planetary nebula appears. Located around 2,000 light years from our solar system, it doesn’t matter if the “Blinking Planetary” is a trick of the eye or not… Because it’s cool!

I hope you enjoy this week’s studies, because I thoroughly intend to do the same at the Black Forest Star Party! Let’s hope we all have clear skies. Now, I’m outta’ here until the Moon returns. Until then? May all your journeys be at light speed…~Tammy Plotner

Posted on by Mark Mortimer

Book Review: The Tunguska Fireball

The Tunguska fireball occured in 1908 in the further reaches of Russia. Bright lights, loud sounds and searing heat signalled this event. Cutting edge measuring devices detected anomalies as far away as Britian, while most people of Europe had the pleasure of seeing a fairy tale like night time sky. Years later, some ground explorers loped into action to find a remarkably wide- spread landscape of shattered trees and burnt surfaces. Further, the tress fell in a pattern as to suggest being blown down by an extremely powerful force. However, given the inhospitable climate of the region, the assessment was brief and decades separated subsequent investigators. Further, given the political climate of the times, almost 50 years passed before international researchers arrived. Nonetheless, with the fertile imagination with which humans are blessed, we have taken what information was available, together with our growing cadre of knowledge in astrophysics, to raise a plethora of rationale for this fireball.

Surendra Verma presents his compilation of the events and possible causes in a smoothly flowing and succintly detailed rendition. He begins by repeating the known facts and figures. People, times, and places fill out the background for the reader and stress the challenges in solving this mystery. Much seems to stem from the brevity of facts and the inaccesibility of the region. In a loosely chronological sequence, Verma pins together the details in a fashion more reminiscent of note taking than of novel writing. He appears to stay to the facts and takes little literary excess with hyperbole of either facts or reactions. However, the reader can easily make their own decuctions. For instance, I was fascinated to learn of the small amount of interest shown by the locals. Instead of acknowledging the fireball and learning from it, their response was to treat it as a sort of mythical situation that was better left alone. Nevertheless, given that there always seems to be some overly curious types, people did consider this event and Verma does bring their observations to the fore.

Once he has established this basis, Verma than treats us to the smorgasbord of hypotheses that arose. He doesn’t solve it himself, as suggested by the sub-title. Rather, he seems to have two other purposes. One is to demonstrate that many natural processes give rise to similar effects. People saw lights, heard explosions and felt heat. The source might have been asteroids, comets, nuclear explosions, anti-matter, mirror matter, black holes, aliens, and so on. The other purpose he provides is to discuss the natural processes themselves. These tidbits will keep the up and coming scientiest curious for many pages. Verma usually isolates each process in individual chapters. As an example, the chapter on asteroids discusses their typical composition, locations within in our solar system and frequency of striking planets. Occassional asides mention the possibility of a companion star for our sun that occasionaly redirects asteroids toward Earth. At the book’s end, Verma does sum up the data and selects his most likely suspect, just like the second last chapter in a mystery novel.

With the combination of scientific and historical background, Verma presents an easy to read treatise on both the fireball and on physical phenomena that could cause such a huge effect upon the flora and fauna on the Earth. Sometimes the description of the science seems to overshadow the event. For instance, a large section describes the extinction of dinosaurs. True, this extinction event, in ways, is just as mysterious as the fireball. However, asteroids and comets were already discussed. The discovery of the Chicxculub crater and its implications seems superlative to the main theme. Given the scarceness of data, there is no surprise on this relative emphasis on the science.

The fireball that blew into Russia’s north may be due to an understood physical event. However, as Surendra Verama shows us in his book Tunguska Fireball we are not exactly sure which event. Much in its history remains obscure, while each of many popular hypotheses rely on contradictory points. Nevertheless, as with any good mystery, there are lots of suspects and enough questions to keep contemplating and enjoy perusing within.

Review by Mark Mortimer

Read more reviews online, or purchase a copy from Amazon.com.

Posted on by Fraser Cain

Saturn’s Moon Pan

Moon Pan behind ring A. Image credit: NASA/JPL/SSI Click to enlarge
Cassini turns its gaze toward Saturn’s outer A ring to find the moon Pan coasting behind one of the thin ringlets which it shares with the Encke Gap. Pan is 26 kilometers (16 miles) across.
Understanding the influence of Saturn’s moons on its immense ring system is one of the goals of the Cassini mission. The study of the icy rings includes the delicate and smoky-looking F ring, seen here toward the upper right. The F ring exhibits bright kinks and multiple strands here.

Arching across the center of the scene, the outermost section of the A ring is notably brighter than the ring material interior to it.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 13, 2005, at a distance of approximately 2.3 million kilometers (1.5 million miles) from Saturn. The image scale is 14 kilometers (9 miles) per pixel on Pan.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Venus, Jupiter and the Moon Reunited Again

Similar close encounter last November. Image credit: Babak A. Tafreshi Click to enlarge
Something nice is happening in the sunset sky. Venus and Jupiter, the two brightest planets, are converging, and they’re going to be beautifully close together for the next two weeks.

Step outside tonight when the sun goes down and look west. If there are no trees or buildings in the way, you can’t miss Jupiter and Venus. They look like airplanes, hovering near the horizon with their lights on full blast. (Venus is the brighter of the two.) You can see them even from brightly-lit cities.

Try catching the pair just after sundown and just before the first stars appear. Venus and Jupiter pop into view while the sky is still twilight-blue. The scene has a special beauty.

When the sky darkens completely, look to the left of Jupiter for Spica, the brightest star in the constellation Virgo. Although it’s a bright star, Spica is completely outclassed by the two planets.

Venus and Jupiter are converging at the noticeable rate of 1o per day, with closest approach coming on September 1st when the two will be a little more than 1o apart. (How much is 1o? Hold your pinky finger at arm’s length. The tip is about 1o wide.)

When planets are so close together, not only do you notice them, you’ll have a hard time taking your eyes off them. They’re spellbinding.

There’s a biological reason for this phenomenon: In the back of your eye, near the center of the retina, lies a small patch of tissue called “the fovea” where cones are extra-densely packed. “Whatever you see with the fovea, you see in high-definition,” explains Stuart Hiroyasu, O.D., of Bishop, California. “The fovea is critical to reading, driving, watching television; it has the brain’s attention.” The field of view of the fovea is 5o. When two objects converge to, say, 1o as Venus and Jupiter will do, they can beam into your fovea simultaneously, signaling your brain?attention, please!

After September 1st, the two planets separate, but the show’s not over. On September 6th, with Jupiter and Venus still pleasingly close together, the slender crescent Moon will leap up from the sun’s glare and join the two planets. Together, they’ll form a compact triangle that will simply knock your socks off.

Feel like staring? Do.

Original Source: NASA News Release