Posted on by Fraser Cain

What’s Up This Week – September 26 – October 2, 2005

M2. Image credit: Doug Williams/REU Program NOAO/AURA/NSF. Click to enlarge.
Monday, September 26 – Tonight our journey might seem like a simple one, but the rewards are great. First you must start by identifying bright Beta Aquarii about a fist’s width above the northeastern most corner star of Capricornus. Continue northward about another five degrees, because I’m going to introduce you to the M2.

First seen by Maraldi in 1746 and later cataloged by Messier in 1760, the M2 is easily seen in both binoculars and small telescopes. The awesome globular cluster is around 50,000 light years away, putting it far more distant than the M13, and it’s positioned in the general direction of our own galaxy’s southern pole. Containing at very least 100,000 stars, including red and yellow giants, even small optics will immediately pick up on the M2’s strong, bright core and larger scopes will resolve out an impressive amount of the fainter members. It’s a good one!

Tuesday, September 27 – Tonight’s destination is not an easy one, but if you have a 6″ or larger scope, you’ll fall in love a first sight! Let’s head for Eta Pegasi and slightly more than 4 degrees north/northeast for the NGC 7331.

This beautiful, 10th magnitude, tilted spiral galaxy is very much how our own Milky Way would appear if we could travel 50 million light years away and look back. Very similar in both structure to ourselves and the “Great Andromeda”, this particular galaxy gains more and more interest as scope size increases – yet it can be spotted with larger binoculars. At around 8″ in aperture, a bright core appears and the beginnings of wispy arms. In the 10″ to 12″ range, spiral patterns begin to emerge and with good seeing conditions, you can see “patchiness” in structure as nebulous areas are revealed and the western half is deeply outlined with a dark dustlane. But hang on… Because the best is yet to come!

Wednesday, September 28 – Tonight return to the NGC 7331 with all the aperture you have. What we are about to look at is truly a challenge and requires dark skies, optimal position and excellent conditions. Now breathe the scope about one half a degree south/southwest and behold one of the most famous galaxy clusters in the night.

In 1877, French astronomer – Edouard Stephan was using the first telescope designed with a reflection coated mirror when he discovered something a bit more with the NGC 7331. He found a group of nearby galaxies! This faint gathering of five is better known as “Stephan’s Quintet” and its members are no further apart than our own Milky Way galaxy.

Visually in a large scope, these members are all rather faint, but their proximity is what makes them such a curiosity. The Quintet is made up of five galaxies numbered NGC 7317, 7318, 7318A, 7318B, 7319 and the largest is 7320. Even with a 12.5″ telescope, this author has never seen them as much more than tiny, barely there objects that look like ghosts of rice grains on a dinner plate. So why bother?

What our backyard equipment can never reveal is what else exists within this area – more than 100 star clusters and several dwarf galaxies. Some 100 million years ago, the galaxies collided and left long streamers of their materials which created star forming regions of their own, and this tidal pull keeps them connected. The stars within the galaxies themselves are nearly a billion years old, but between them lay much younger ones. Although we cannot see them, you can make out the soft sheen of the galactic nucleii of our interacting group.

Enjoy their faint mystery!

Thursday, September 29 – Tonight let’s relax a little bit and have a look at a superb open cluster that stays superb no matter if you use small binoculars or a big telescope. Of whom do I speak so highly? M34…

Easily found on Perseus west border by scanning between Beta Perseii (Algol) and Gamma Andromeda (Almach), the M34 was discovered by Messier in 1764. Containing around 80 members, the central knot of stars is what truly makes it beautiful. At around 1400 light years away, this stellar collection is believed to be around 10 million years old. While binocular users are going to be very happy with this object, scopists are going to appreciate the fact that there is a double right in the heart of M34. This fixed pair is around magnitude 8 and separated by about 20″.

Friday, September 30 – Today in 1880, Henry Draper must have been up very early indeed when he took the first photo of the Great Orion Nebula (M42). Although you might not wish to set up equipment before dawn, you can still use a pair of binoculars to view this awesome nebula! You’ll find Orion high in the southeast for the Northern Hemisphere, and the M42 in the center of the “sword” that hangs below its bright “belt” of three stars.

While you’re out, take advantage of some very beautiful sky scenery. To the west, Mars dominates the sky as the brightest object and the Pleiades so nearby doubles the pleasure. More? Then look east and catch Saturn’s act and it still remains very close to the “Beehive”. All of these can be see with the unaided eye and make getting up early a pleasure!

Saturday, October 1 – In 1897, the world’s largest refractor (40″) debuted at the dedication of the University of Chicago’s Yerkes Observatory. Also today in 1958, NASA established by an act of Congress. More? In 1962, the 300-foot radio telescope of the National Radio Astronomy Observatory (NRAO) went live at Green Bank, West Virginia. It held its place as the world’s second largest radio scope until it collapsed in 1988.

One this universal date, viewers in Alaska will have the opportunity to watch the very last of the Moon occult Sigma Leonis. Be sure to check this IOTA webpage for times and locations.

For those of you who have waited on the weekend to enjoy dark skies, then let’s add another awesome galaxy to the collection. Tonight set your sights towards Alpha Pegasi and drop due south less than 5 degrees to pick up NGC 7479.

Discovered by William Herschel in 1784. this tantalizing 11 magnitude barred spiral galaxy has had a supernova in its nucleus as recently as 1990. While the 16th magnitude event is no longer visible, smaller telescopes will easily pick out bright core and elongation of the central bar. Larger aperture will find this one a real treat as the spiral arms curl both over and under the central structure, resembling a ballet dancer “en pointe”.

Congratulations! You’ve just observed Caldwell 44.

Sunday, October 2 – Do I always save the best for last? You bet. And tonight it’s my favourite galaxy structure – edge-on.

The NGC 7814 is easy enough to find. Just head towards Gamma Pegasi and look in your finderscope for a star that is around 3 degrees to the northwest. At low power you will see the galaxy to the southeast of this star as a scratch of light. Up the power in both aperture and magnification and enjoy! This galaxy has a deeply concentrated nucleus and a very prominent dissecting dark dustlane.

By the way… It’s Caldwell 43. 😉

Here’s hoping that all of you have clear, dark skies! Until next week? May all your journeys be at light speed…. ~Tammy Plotner

Posted on by Mark Mortimer

Report from Toronto’s Lunar Conference

Paul Campbell took this amazing picture of the Moon. Image credit: Paul Campbell. Click to enlarge.
ILEWG is a public forum sponsored by the world’s space agencies to support “international cooperation towards a world strategy for the exploration and utilization of the Moon – our natural satellite”. An example objective is the ready and free sharing of data to any and all parties. This allows for judicious review and most importantly avoids duplication. Also, by coordinating onboard experiments beforehand, agencies can avoid duplicating research and wasting scarce funding. Given the costs and risks associated with each expedition, together with the scarcity of public funds, avoiding duplication is a necessary goal.

Exploring the Moon never stopped after the Apollo program. However, researchers have had to fight for funding on an equal basis with every other government department. In consequence, the number of missions have been few and far between. Now, only one satellite, Smart-1, orbits the Moon. This will change. For returning to the Moon, setting up a base, and then continuing on to Mars, we will need to know more of the Moon to minimize the cost and maximize the benefit. The Holy Grail for lunar exploration is water ice. Finding sufficient, recoverable quantities would greatly facilitate a human presence (as in drinking water) and further exploration (as in rocket fuel production). Without water ice, we either use brute force to raise sufficient quantities out of Earth’s gravity well or invent new techniques. Both these represent signficantly greater challenges. Nevertheless, the researchers at ILEWG are well aware of their knowledge gaps and are actively preparing missions to fill these in.

Yet the ILEWG participants aren’t accepting the status quo with NASA being the only player in town. In addition to other national space agencies, there were many individuals and corporations who were promoting their own style of space exploration and utilization. Lunar telescopes, mines and tourist hotels were just some opportunities deemed potential. To facilitate these ventures, conference attendees were treated to lectures on property rights, the common heritage of humankind and investment financing. For instance, without any arbitration medium, imagine sitting at your new observatory on the moon only to feel blasting from a nearby mining operation! These additional conference contributors, and their ability to think outside the box, demonstrate the desire and ability of the big, independent players at ILEWG.

However, even though great thinkers and doers were present, this doesn’t guarantee a lunar ‘gold rush’ happening any time soon. After all, if there were quick riches to be made, we would have had colonies already turning the lunar regolith into Swiss cheese. Instead, we’ve had to rely on public funds, i.e. taxpayer’s dollars. And unless some unforeseen magic appears, we will need a huge amount of this money to build a suitable infrastructure to reliably establish a human presence on the Moon’s surface. This showcases one omission from ILEWG. Very little attention was given to promoting lunar and space activities to the general public. Given the incessant demand for public funds that comes from every quarter, there needs to be solid and continual vindication for lunar base allocations. Alongside the great thinkers and doers, we need exuberant public relations experts to sell this endeavour.

Without the public’s interest, we will neither establish lunar colonies nor ever move off of Earth. The preponderance of technical data and investigations at the ILEWG conference demonstrate that we have the technical ability. But where is the justification? There is precious little economic justification. The monetary cost and consumption of Earth’s natural resources for people to live and work on the Moon is far greater than the equivalent cost of doing business on Earth. Further, the Moon has no unique qualities, after all, the Moon’s surface is very similar to the Earth’s. So, though service and resource providers may facilitate lunar colonies, they will not economically create such a colony.

But I am a believer. We need to step off of Earth and give ourselves a future that encompasses more than this one planet. We know our planet’s environment changes drastically. We know large asteroids regularly pummel the Earth’s surface. We know our Sun’s radiation fluctuates and the Sun itself will undergo a final tumultuous collapse. Restricting our children to the confines of the Earth’s surface is an artificial limiter that prevents our species from being the best it can be. We can do better. So get involved, talk to people, remind them that space is still a new harsh environment onto which we have barely stepped. Make them believe in a future more challenging and rewarding than simply lying on the ground at night wondering what the shiny dots above might be.

Whether, homesteaders, governments or organizations are the instigators, the Moon is our stepping stone off the Earth. The organization ILEWG is helping coordinate research and exploration amongst nations to quicken the building of our society off world. The gravity well that is Earth will remain for as long as the Earth so let’s acknowledge this, not as a barrier, but as a test to our civilization. Let’s work together and pass this test and decide our future, or we will stay moribund on Earth waiting for the future to decide our fate.

Written by Mark Mortimer

Posted on by Fraser Cain

ESA Picks an Asteroid to Move

Computer animation of Don Quijote and its asteroid target. Image credit: ESA. Click to enlarge.
Based on the recommendations of asteroid experts, ESA has selected two target asteroids for its Near-Earth Object deflecting mission, Don Quijote.

Don Quijote is an asteroid-deflecting mission currently under study by ESA?s Advanced Concepts Team (ACT). Earlier this year the NEO Mission Advisory Panel (NEOMAP), consisting of well-known experts in the field, delivered to ESA a target selection report for Europe?s future asteroid mitigation missions, identifying the relevant criteria for selecting a target and picking up two objects that meet most of those criteria. The asteroids? temporary designations are 2002 AT4 and 1989 ML.

With this input and the support of ESA?s Concurrent Design Facility (CDF) experts, the Advanced Concepts Team has now completed an extensive assessment of suitable mission architectures, launch strategies, propulsion system options and experiments.

The current scenario envisages two spacecraft in separate interplanetary trajectories. One spacecraft (Hidalgo) will impact an asteroid, the other (Sancho) will arrive earlier at the target asteroid, rendezvous and orbit the asteroid for several months, observing it before and after the impact to detect any changes in its orbit.

Industrial studies are now about to start; it will be down to European experts to propose alternative solutions for the design of the low-cost NEO precursor mission. This will be the first step towards the development of a means to tackle asteroid impacts ? one of the few natural disasters that our technology can prevent.

A near miss?
While the eyes of the world were on the Asian tsunami last Christmas, one group of scientists were watching uneasily for another potential natural disaster ? the threat of an asteroid impact.

On 19 December 2004 MN4, an asteroid of about 400 m, lost since its discovery six months earlier, was observed again and its orbit was computed. It immediately became clear that the chances that it could hit the Earth during a close encounter in 2029 were unusually high. As the days passed the probability did not decrease and the asteroid became notorious for surpassing all previous records in the Torino and Palermo impact risk scales – scales that measure the risk of an asteroid impact just as the Richter scale quantifies the size of an earthquake.

Only after earlier observations of the object were found and a more accurate trajectory was computed did it become clear that it would not impact the Earth ? at least not in 2029. Impacts on later dates, though unlikely, have not been totally ruled out. It is extremely difficult to tell what will happen unless we come up with a better way to track this or other NEOs and if necessary take steps to tackle them.

Most world experts agree that this capability is now within our reach. A mission like ESA?s Don Quijote could provide a means to assess a threatening NEO and take concrete steps to deflect it away from the Earth.

But every good performance needs rehearsing and in order to be ready for such a threat, we should try our hardware on a harmless asteroid first. Don Quijote would be the first mission to make such an attempt. The big question was: which asteroid and what should it be like?

Looking for the perfect target
The NEO population contains a confusing variety of objects, and deciding which physical parameters are most relevant for mitigation considerations is no trivial task. But the NEOMAP experts took on the challenge and in February 2005 provided ESA with their recommendations on the asteroid selection criteria for ESA?s deflection rehearsal.

People might wonder whether performing a deflection test, such as that planned for Don Quijote, represents any risk to our planet. What if things go wrong? Could we create a problem, rather than learn how to avoid one?

Experts world-wide say the answer is no. Even a very dramatic impact of a heavy spacecraft on a small asteroid would only result in a minuscule modification of the object?s orbit. In fact the change would be so small that the Don Quijote mission requires two spacecraft ? one to monitor the impact of the other. The second spacecraft measures the subtle variation of the object?s orbital parameters that would not be noticeable from Earth.

Target objects can also be selected so that all possible concerns are avoided altogether, by looking into the way the distance between the asteroid?s and the Earth?s orbits changes with time. If the target asteroid is not an ?Earth crosser?, as is the case with NEOs in the ?Amor? class (which have orbits with perihelion distance well in excess of 1 AU), testing a deflection manoeuvre represents no risk to the Earth.

Other considerations related to the orbit of the target asteroid are also important, especially the change of orbital velocity that is required by the spacecraft to ?catch up? with the target asteroid ? the so-called ?delta V?. This should be sufficiently small to minimise the required amount of spacecraft propellant and enable the use of cheaper launchers, but high enough to allow the same spacecraft to be used with a number of possible targets.

Navigation and deflection measurements requirements set some heavy constraints on the target selection. The shape, density, and size are all important factors, but are often poorly known. A spacecraft orbiting an asteroid needs to know about the object?s gravitational field in order to navigate. The ?impactor spacecraft? must know the position of the centre of mass to define the point it is aiming for.

Asteroids come in all sort of flavours, but as far as composition is concerned two main types dominate. Our still rudimentary knowledge of the abundance of asteroids of different types in the near-Earth asteroid population indicates that the next hazardous asteroid is more likely to be a ?C-type?, than an ?S-type?. C-types have dark surfaces with a carbonaceous spectral signature, while S-types have brighter surfaces, their spectra matching closely that of silicates. The surface properties of the target asteroid -and in particular the percentage of light that it reflects – are a critical factor in the final phase of the impactor spacecraft navigation. The brighter it looks the easier it is to aim at. However for a rehearsal the target should not be too easy.

ESA has selected asteroids 2002 AT4 and (10302) 1989 ML as mission targets because they represent best compromise among all the (sometimes conflicting) selection criteria. A decision on which of the two will become the final destination of both Sancho and Hidalgo spacecraft will be made in 2007.

Don Quijote ? the knight errant rides again
The phase of internal studies on the Don Quijote mission is now over, and it is time for the space industry to suggest suitable design solutions. ESA has made an open invitation to European space companies to submit proposals on possible designs. The selection of the most promising ones will take place towards the end of the year. In early 2006, two teams should start working on their interpretations of this technology demonstration mission. A year later, once the results are available, ESA will select the final design to be implemented, and then Don Quijote will be ready to take on an asteroid!

Additional Notes
Don Quijote is a NEO deflection test mission based entirely on conventional spacecraft technologies. It would comprise two spacecraft – one of them (Hidalgo) impacting an asteroid at a very high relative speed while a second one (Sancho) would arrive earlier at the same asteroid and remain in its vicinity before and after the impact to measure the variation on the asteroid?s orbital parameters, as well as to study the object.

Asteroid 2004 MN has now been given an official designation, (99942) Apophis. Recent observations using Doppler radar using Arecibo radio telescope in Puerto Rico have reduced the impact probability during future encounters to very small levels, though they have not totally ruled out an Earth impact. In 2029, the asteroid will have the closest approach ever witnessed for an object of this size, swinging by the Earth at a distance of around 32,000 kilometres. Its trajectory will be well within the geosynchronous orbit used by most telecommunications and weather satellites, and the object will be visible to the naked eye. Further radar measurements are expected in 2013.

Original Source: ESA News Release

Posted on by Fraser Cain

Delta Launches New GPS Satellite

Boeing Delta II rocket launching new GPS satellite. Image credit: Boeing. Click to enlarge.
A Boeing [NYSE: BA] Delta II launch vehicle today successfully delivered the first of the modernized Block IIR Global Positioning System (GPS) satellites to space for the U.S. Air Force.

The Delta II rocket carrying the GPS IIR-14 (M) spacecraft lifted off from Space Launch Complex 17A at Cape Canaveral Air Force Station, Fla., yesterday at 11:37 p.m. EDT. Following a nominal 24-minute flight, the rocket deployed the satellite to a transfer orbit.

“We are honored to be the United States Air Force’s choice to launch the GPS satellites and proud to have delivered the first modernized spacecraft to its targeted orbit. Tonight’s success is a direct result of the hard work and dedication of Boeing’s Delta team,” said Dan Collins, vice president, Boeing Expendable Launch Systems.

The Boeing Delta II 7925-9.5 configuration vehicle used for this mission featured a Boeing first stage booster powered by a Pratt & Whitney Rocketdyne RS-27A main engine and nine Alliant Techsystems (ATK) solid rocket boosters. An Aerojet AJ10-118K engine powered the storable propellant restartable second stage. A Thiokol Star-48B solid rocket motor propelled the third stage prior to spacecraft deployment. The rocket also flew with a nine-and-a-half-foot diameter Boeing payload fairing.

A redundant inertial flight control assembly built by L3 Communications Space & Navigation provided guidance and control for the rocket that enabled a precise deployment of the satellite.

The GPS IIR-14 (M) mission also marked the 100th flight of the Delta II using the ATK 40-inch diameter version solid rocket motors.

Boeing provides launches for the GPS program aboard Delta II vehicles and has a planned GPS manifest through at least 2007.

The GPS network supports U.S. military operations conducted from aircraft, ships, land vehicles and by ground personnel. Additional use includes mapping, aerial refueling and rendezvous, geodetic surveys, and search and rescue operations.

GPS provides military and civilian users three-dimensional position location data in longitude, latitude and elevation as well as precise time and velocity. The satellites orbit the earth every 12 hours, emitting continuous navigation signals. The signals are so accurate, time can be figured to within one millionth of a second, velocity within a fraction of a mile-per-second and location to within 100 feet.

The new GPS IIR-14 (M) is the first of the modernized GPS satellites that incorporates various improvements to provide greater accuracy, increased resistance to interference and enhanced performance for users.

A unit of The Boeing Company, Boeing Integrated Defense Systems is one of the world’s largest space and defense businesses. Headquartered in St. Louis, Boeing Integrated Defense Systems is a $30.5 billion business. It provides network-centric system solutions to its global military, government and commercial customers. It is a leading provider of intelligence, surveillance and reconnaissance systems; the world’s largest military aircraft manufacturer; the world’s largest satellite manufacturer and a leading provider of space-based communications; the primary systems integrator for U.S. missile defense; NASA’s largest contractor; and a global leader in sustainment solutions and launch services.

Original Source: Boeing News Release

Posted on by Mark Mortimer

Book Review: The Dancing Universe

To understand physics is to understand the motion of the objects surrounding our everyday lives. Studying wheels that turn on the ground is simple. Studying galaxies that spin is another thing altogether. However, the principles of a galaxy’s motion and that of a wheel are amazingly similar. Sometimes all we need do is build an imaginary scenario in our minds to postulate one truth, once given another.

Gleiser really promotes this idea of mental model building in his book as he chronologically steps through 3000 years of history. Further, by placing the reader beside the historical figure, he gives a feel for the real person. He does this by locating the person geographically, identifying supporters and detractors, and adding descriptions of any relevant tools. For example, Philolaus of Croton, around 450 BC, lived in Southern Italy but was encouraged by an unfriendly mob to move to Greece. Using Pythagorean principles, he postulated a framework of celestial objects that explained day and night on Earth. In so doing he was the first to place the sun at the centre of the universe. Philolaus had no tools at hand, but he did live with a collection of like minded thinkers. In a style like this, Gleiser not only shows the contributions of many people but he also shows how society’s collective knowledge replaced the belief that god(s) were responsible.

The chronological sequence gets a rough start as Gleiser begins by thoroughly assessing primitive philosophy. The first chapter delves into creation myths of long ago when people without much information tried to build a comprehension of their existence. With this, a reader may expect a strong leaning toward philosophy throughout. This is not the case, as aside from particular researchers involved with both physics and philosophy, the remaining contents fixates purely on the progress of physics. As expected, there are: the Greeks and their postulating, the trials between the Roman Catholic church and science, the empowerment of universities, and the transcendence of the individual. Some early researchers referred to may be unknown, but otherwise Gleiser includes all the big names.

This study of the main contributors turns out to be Gleiser’s actual intent. He uses this book as the text in a large physics class for non-science majors. Hence, though he alludes to the value of physics, he focuses on the people and their contributions. He likely has been doing this for some time as all his descriptions are extremely clear, simple and easy to follow. For instance, he uses the traditional means of describing special relativity; this being a person in a train and another at the station. Yet, he clearly describes the experimental basis for never having light at rest and thus needing light to have the same speed independent of the observer. No equations reside in the pages, nor pictures, though a few simple diagrams facilitate understanding. Because of this, Glacier’s non-science majors are likely very thankful.

However, Glacier short changes his students. Though his knowledge of physics and refined presentation skills comes across very well, he doesn’t tempt the students (or other readers) to deepen their understanding. For example, there is no push for them to spend more time wondering why the physical laws exist and are (apparently) universal. I liked the very brief discussion regarding the big bang and the time immediately before and after. Sadly, I didn’t really see any hooks that might draw in a reader. As such, this book is a great review and summary but does very little to encourage the advancement of knowledge, i.e., the making of new researchers.

The very word cosmology engenders visions of apparently unending borders. Going on a mission to explore where none have gone before seems like the only game in town. Marcelo Gleiser in his book The Dancing Universe provides some real background for those non-specialists who want to know more about the borders. And should society’s interest continue to grow, there just might come a time when people can travel to find if a border exists.

Review by Mark Mortimer

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

Posted on by Fraser Cain

Satellite Picture of Hurricane Rita

Hurricane Rita, taken on September 22. Image credit: ESA. Click to enlarge.
As Hurricane Rita entered the Gulf of Mexico, ESA’s Envisat satellite’s radar was able to pierce through swirling clouds to directly show how the storm churns the sea surface. This image has then been used to derive Rita’s wind field speeds.

Envisat acquired this Advanced Synthetic Aperture Radar (ASAR) image at 0344 UTC on 22 September (2345 on 21 September in US Eastern Daylight Saving Time), when Hurricane Rita was passing west of Florida and Cuba. The image was acquired in Wide Swath Mode with resolution of 150 metres. Envisat’s optical Medium Resolution Imaging Spectrometer (MERIS) is also being used to observe the storm during daylight, returning details of its cloud structure and pressure.

Notably large waves are seen around the eye of Hurricane Rita in the radar image. ASAR measures the backscatter, which is a measure of the roughness of the ocean surface. On a basic level, bright areas of the radar image mean higher backscatter due to surface roughness. This roughness is strongly influenced by the local wind field so that the radar backscatter can be used in turn to measure the wind.

So the Center for Southeastern Tropical Advanced Remote Sensing at the University of Miami used this ASAR image to calculate the speed of Hurricane Rita’s surface wind fields ? showing maximum wind speeds in excess of 200 kilometres per hour.

“The most detailed information about hurricane dynamics and characteristics are obtained from dedicated flights by hurricane hunter aircraft,” explains Hans Graber of CSTARS. “However these flight missions cannot always take place. Satellite remote sensing provides a critical alternative approach.

“It is critical for weather forecasters to obtain reliable characterization of the eye wall dimension and the radii of gale- tropical storm- and hurricane-force winds in order to provide skilful forecasts and warning. Satellite based observations will facilitate better understanding of hurricane evolution and intensification.

“Radar images penetrate through clouds and can easily detect the eye replacement cycle of hurricanes which are precursors to further intensification.”

Rita was a maximum Category Five on the Saffir-Simpson Hurricane Scale when the ASAR image was acquired. As it continues west through the Gulf of Mexico it has weakened to a still-dangerous Category Four. Rita is expected to make landfall on the Gulf coast during the morning of 24 September.

ERS-2 joins in Rita observations
The same day Envisat acquired its ASAR image of Rita, its sister spacecraft ERS-2 also made complementary observations of the hurricane’s underlying wind fields using its radar scatterometer.

This instrument works by firing a trio of high-frequency radar beams down to the ocean, then analysing the pattern of backscatter reflected up again. Wind-driven ripples on the ocean surface modify the radar backscatter, and as the energy in these ripples increases with wind velocity, so backscatter increases as well. Scatterometer results enable measurements of not only wind speed but also direction across the water surface.

What makes ERS-2’s scatterometer especially valuable is that its C-band radar frequency is almost unaffected by heavy rain, so it can return useful wind data even from the heart of the fiercest storms ? and is the sole scatterometer of this type currently in orbit.

The ERS-2 Scatterometer results for Hurricane Rita seen here have been processed by the Royal Netherlands Meteorological Institute (KNMI). They are also routinely assimilated by the European Centre for Medium-Range Weather Forecasting (ECMWF) into their advanced numerical models used for meteorological predictions.

“Scatterometer data from the ERS-2 platform provide high-quality wind information in the vicinity of tropical cyclones,” states Hans Hersbach of ECMWF. “For a Hurricane like Rita, the combination of such observations with [in-situ] dropsonde data enables the analysis system at ECMWF to produce an improved forecast.”

Another Envisat instrument called the Radar Altimeter-2 uses radar pulses to measure sea surface height (SSH) down to an accuracy of a few centimetres.

Near-real time radar altimetry is a powerful tool for monitoring a hurricane’s progress and predicting its potential impact. This is because anomalies in SSH can be used to identify warmer ocean features such as warm core rings, eddies and currents.

The US National Oceanic and Atmospheric Administration (NOAA) is utilising Envisat RA-2 results along with those from other space-borne altimeters to chart such regions of ‘tropical cyclone heat potential’ (TCHP) and improve the accuracy of Hurricane Rita forecasting.

Observing hurricanes
A hurricane is basically a large, powerful storm centred around a zone of extreme low pressure. Strong low-level surface winds and bands of intense precipitation combine strong updrafts and outflows of moist air at higher altitudes, with energy released as rainy thunderstorms.

Envisat carries both optical and radar instruments, enabling researchers to observe high-atmosphere cloud structure and pressure in the visible and infrared spectrum, while at the same time using radar backscatter to measure the roughness of the sea surface and so derive the wind fields just above it.

Those winds converging on the low-pressure eye of the storm are what ultimately determine the spiralling cloud patterns that are characteristic of a hurricane.

Additional Envisat instruments can be used to take the temperature of the warm ocean waters that power storms during the annual Atlantic hurricane season, along with sea height anomalies related to warm upper ocean features.

Original Source: ESA News Release

Here are some hurricanes pictures.

Posted on by Fraser Cain

Many Galaxies Found in the Early Universe

13 distant galaxies found in a sample of sky. Image credit: ESO. Click to enlarge.
It is one of the major goals of observational cosmology to trace the way galaxies formed and evolved and to compare it to predictions from theoretical models. It is therefore essential to know as precisely as possible how many galaxies were present in the Universe at different epochs.

This is easier to say than to do. Indeed, if counting galaxies from deep astronomical images is relatively straightforward, measuring their distance – hence, the epoch in the history of the universe where we see it [1] – is much more difficult. This requires taking a spectrum of the galaxy and measuring its redshift [2].

However, for the faintest galaxies – that are most likely the farthest and hence the oldest – this requires a lot of observing time on the largest of the telescopes. Until now, astronomers had thus to first carefully select the candidate high-redshift galaxies, in order to minimise the time spent on measuring the distance. But it seems that astronomers were too careful in doing so, and hence had a wrong picture of the population of galaxies.

It would be better to “simply” observe in a given patch of the sky all galaxies brighter than a given limit. But looking at one object at a time would make such a study impossible.

To take up the challenge, a team of French and Italian astronomers [3] used the largest possible telescope with a highly specialised, very sensitive instrument that is able to observe a very large number of (faint) objects in the remote universe simultaneously.

The astronomers made use of the VIsible Multi-Object Spectrograph (VIMOS) on Melipal, one of the 8.2-m telescopes of ESO’s Very Large Telescope Array. VIMOS can observe the spectra of about 1,000 galaxies in one exposure, from which redshifts, hence distances, can be measured. The possibility to observe two galaxies at once would be equivalent to using two VLT Unit Telescopes simultaneously. VIMOS thus effectively multiplies the efficiency of the VLT hundreds of times.

This makes it possible to complete in a few hours observations that would have taken months only a few years ago. With capabilities up to ten times more productive than competing instruments, VIMOS offers the possibility for the first time to conduct an unbiased census of the distant Universe.

Using the high efficiency of the VIMOS instrument, the team of astronomers embarked in the VIMOS VLT Deep Survey (VVDS) whose aim is to measure in some selected patch of the sky the redshift of all galaxies brighter than magnitude 24 in the red, that is, galaxies that are up to 16 million fainter than what the unaided eye can see.

In a total sample of about 8,000 galaxies selected only on the basis of their observed brightness in red light, almost 1,000 bright and vigorously star forming galaxies were discovered at an epoch 1,500 to 4,500 million years after the Big Bang (redshift between 1.4 and 5).

“To our surprise”, says Olivier Le F?vre, from the Laboratoire d’Astrophysique de Marseille (France) and co-leader of the VVDS project, “this is two to six times higher than had been found by previous works. These galaxies had been missed because previous surveys had selected objects in a much more restrictive manner than we did. And they did so to accommodate the much lower efficiency of the previous generation of instruments.”

While observations and models have consistently indicated that the Universe had not yet formed many stars in the first billion years of cosmic time, the discovery made by the scientists calls for a significant change in this picture.

Combining the spectra of all the galaxies in a given redshift range (i.e. belonging to the same epoch), the astronomers could estimate the amount of star formed in these galaxies. They find that the galaxies in the young Universe transform into stars between 10 and 100 times the mass of our Sun in a year.

“This discovery implies that galaxies formed many more stars early in the life of the Universe than had previously been thought”, explains Gianpaolo Vettolani, the other co-leader of the VVDS project, working at INAF-IRA in Bologna (Italy). “These observations will demand a profound reassessment of our theories of the formation and evolution of galaxies in a changing Universe.”

It now remains for astronomers to explain how one can create such a large population of galaxies, producing more stars than previously assumed, at a time when the Universe was about 10-20% of its current age.

Original Source: ESO News Release

Posted on by Fraser Cain

Chandra View of Tycho’s Remnant

Tycho’s Supernova as viewed by the Chandra X-Ray Observatory. Image credit: NASA. Click to enlarge.
In 1572, the Danish astronomer Tycho Brahe observed and studied the explosion of a star that became known as Tycho’s supernova. More than four centuries later, Chandra’s image of the supernova remnant shows an expanding bubble of multimillion degree debris (green and red) inside a more rapidly moving shell of extremely high energy electrons (filamentary blue).

The supersonic expansion (about six million miles per hour) of the stellar debris has created two X-ray emitting shock waves – one moving outward into the interstellar gas, and another moving back into the debris. These shock waves produce sudden, large changes in pressure and temperature, like an extreme version of sonic booms produced by the supersonic motion of airplanes.

According to the standard theory, the outward-moving shock wave should be about 2 light years ahead of the stellar debris. What Chandra found instead is that the stellar debris has kept pace with the outer shock and is only about half a light year behind.

The most likely explanation for this behavior is that a large fraction of the energy of the outward-moving shock wave is going into the acceleration of atomic nuclei to speeds approaching the speed of light. The Chandra observations provide the strongest evidence yet that nuclei are indeed accelerated and that the energy contained in the high-speed nuclei in Tycho’s remnant is about 100 times that observed in high-speed electrons.

This finding is important for understanding the origin of cosmic rays, the high-energy nuclei which pervade the Galaxy and constantly bombard the Earth. Since their discovery in the early years of the 20th century, many sources of cosmic rays have been proposed, including flares on the sun and similar events on other stars, pulsars, black hole accretion disks, and the prime suspect – supernova shock waves. Chandra’s observations of Tycho’s supernova remnant strengthen the case for this explanation.

Original Source: Chandra News Release