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

Posted on by Fraser Cain

Earth’s Core Rotates Faster Than Its Crust

Earth. Image credit: NASA Click to enlarge
Scientists have ended a long debate by proving that Earth’s core rotates faster than its surface.

Their research measured differences in the time it took seismic waves generated by nearly identical earthquakes to travel through Earth’s inner core.

According to geologists Jian Zhang of the Lamont-Doherty Earth Observatory (LDEO), Xiaodong Song of the University of Illinois at Urbana-Champaign and other co-authors of a paper in the Aug. 26 issue of the journal Science, Earth’s iron core is rotating approximately 1 degree per year faster than the rest of the planet.

“Whether the Earth’s core spins faster than its surface has been a hotly debated topic,” says Robin Reichlin, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “These new observations provide compelling support that it does.”

The scientists studied waveform doublets–earthquakes that are detected at the same seismic recording station in two different places, at two different times. A Sept. 2003, earthquake in the Atlantic Ocean near the South Sandwich Islands that was also detected in Ala., provided a near-exact match with one that had occurred in Dec.1993.

The seismograms were almost identical for shocks that had traveled only in the mantle and outer core. But seismic waves that had traveled through the inner core looked slightly different: they had made the trip through the Earth faster in 2003 than in 1993.

“The similar seismic waves that passed through the inner core show changes in travel times,” says Song. “The only plausible explanation is the faster rotation of the inner core.”

In all, the geologists analyzed 18 “doublets” from the South Sandwich Islands that were detected at Ala. seismic stations between 1961 and 2004.

“For decades, people thought of the Earth’s interior as changing very slowly over millions of years,” said scientist Paul Richards of LDEO, a co-author of the paper. “These results show that we live on a remarkably dynamic planet. They also underscore the fact that we know more about the moon than we know about what’s beneath our feet. Now we need to understand what is driving this difference.”

In addition to Zhang, Song and Richards, co-authors of the paper are Illinois graduate students Yingchun Li and Xinlei Sun and research scientist Felix Waldhauser. The work was also funded by the Natural Science Foundation of China.

Original Source: NSF News Release