Posted on by Fraser Cain

Fresh Crater on Rhea

Image credit: NASA/JPL/SSI
Rhea has been heavily bombarded by impacts during its history. In this Cassini image the moon displays what may be a relatively fresh, bright, rayed crater near Rhea’s eastern limb. Rhea is 1,528 kilometers (949 miles) across.

This view is centered on the side of Rhea that faces away from Saturn as the moon orbits. The image was taken in visible light with the Cassini spacecraft narrow angle camera on Nov. 10, 2004, at a distance of 3.6 million kilometers (2.2 million miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 86 degrees. North is up. The image scale is 21 kilometers (13 miles) per pixel. The image has been magnified by a factor of two and contrast enhanced to aid visibility of surface features.

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 team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Magnetic Fields Could Shape Nebulae

Planetary nebulae are expanding gas shells that are ejected by Sun-like stars at the end of their lifetimes. Sun-like stars spend most of their lifetime burning hydrogen into helium. At the end of this hydrogen fusion phase, these stars increase their diameter by about a factor of 100 and become “red giant stars”. At the end of the red giant phase, the outer layers of the star are blown away. The ejected gas continues to expand out from the remaining central star, which later evolves into a “white dwarf” when all nuclear fusion has ceased. Astronomers believe that a planetary nebula forms when a fast stellar wind that comes from the central star catches up a slower wind produced earlier when the star ejected most of its outer layers. At the boundary between the two winds, a shock occurs that produces the visible dense shell characteristic of planetary nebulae. The gas shell is excited and lighted up by the light emitted by the hot central star. The light from the central star is able to light up the planetary nebula for some 10,000 years.

The observed shapes of planetary nebulae are very puzzling: most of them (about 80%) are bipolar or elliptical rather than spherically symmetric. This complexity has lead to beautiful and amazing images obtained with modern telescopes. The pictures below compare planetary nebulae with bipolar (left) and spherical (right) shapes.

The reason why most planetary nebulae are not spherical is not well understood. Several hypotheses have been considered so far. One of them suggests that the strange shapes of planetary nebulae might be due to some centrifugal effect that results from the fast rotation of red giants. Another theory is that the symmetry of the star’s wind may be affected by a companion star. However, the most recent and convincing theories explaining the shapes of the nebulae involve magnetic fields.

The presence of magnetic fields would nicely explain the complicated shapes of planetary nebulae, as the ejected matter is trapped along magnetic field lines. This can be compared to iron filings trapped along the field lines of a bar magnet – a classic demonstration in high school physics classrooms. Since strong magnetic fields at the surface of the star also exert pressure on the gas, matter can more easily leave the star at the magnetic poles where the magnetic field is strongest.

There are several ways magnetic fields can be created in the vicinity of planetary nebulae. Magnetic fields can be produced by a stellar dynamo during the phase when the nebula is ejected. For a dynamo to exist, the core of the star must rotate faster than the envelope (as is the case in the Sun). It is also possible that the magnetic fields are fossil relics of previous stages of stellar evolution. Under most circumstances, the matter in stars is so highly electrically conductive that magnetic fields can survive for millions or billions of years. Both mechanisms, combined with the interaction of the ejected matter with the surrounding interstellar gas, would be able to shape the planetary nebulae.

Until recently, the idea that magnetic fields are an important ingredient in the shaping od planetary nebulae was a purely theoretical claim. In 2002, the first indications of the presence of such magnetic fields were found. Radio observations revealed magnetic fields in circumstellar envelopes of giant stars. These circumstellar envelopes are indeed progenitors of planetary nebulae. However, no such magnetic field has ever been observed in the nebulae themselves. To obtain direct clue of the presence of magnetic fields in planetary nebulae, astronomers decided to focus on the central stars, where the magnetic fields should have survived.

This first direct evidence has now been obtained. For the first time, Stefan Jordan and his team detected magnetic fields in several central stars of planetary nebulae. Using the FORS1 spectrograph of the 8-m class Very Large Telescope (VLT, European Southern Observatory, Chile), they measured the polarization of the light emitted by four of these stars. The polarization signatures in the spectral lines make it possible to determine the intensity of the magnetic fields in the observed stars. In the presence of a magnetic field, atoms change their energy in a characteristic way; this effect is called the Zeeman effect and was discovered in 1896 by Pieter Zeeman in Leiden (Netherlands). If these atoms absorb or emit light, the light becomes polarized. This makes it possible to determine the strength of the magnetic field by measuring the strength of the polarization. These polarization signatures are usually very weak. Such measurements require very high quality data that can only be obtained using 8-meter class telescopes such as the VLT.

Four central stars of planetary nebulae were observed by the team and magnetic fields were found in all of them. These four stars were chosen because their associated planetary nebulae (named NGC 1360, HBDS1, EGB 5, and Abell 36) are all non-spherical. Therefore, if the magnetic field hypothesis to explain the shapes of planetary nebulae is correct, these stars should have strong magnetic fields. These new results show that it is indeed the case: the strengths of the detected magnetic fields range from 1000 to 3000 Gauss, that is about one thousand times the intensity of the Sun’s global magnetic field.

These new observations published by Stefan Jordan and his colleagues support the hypothesis that magnetic fields play a major role in shaping planetary nebulae. The team now plans to search for magnetic fields in the central stars of spherical planetary nebulae. Such stars should have weaker magnetic fields than the ones just detected. These future observations will allow astronomers to better quantify the correlation between magnetic fields and the strange shapes of planetary nebulae.

In the few past years, polarimetric observations with the VLT have led to the discovery of magnetic fields in a large number of stellar objects in late evolutionary stages. In addition to improving our understanding of these beautiful planetary nebulae form, the detection of these magnetic fields allows science to take a step forward towards the clarification of the relationship between magnetic fields and stellar physics.

Original Source: NASA Astrobiology Story

Posted on by Fraser Cain

Giant Star Generates a Massive Amount of X-Rays

Beta Ceti is a bright, giant star with a hot corona that radiates about 2,000 times more X-ray power than the Sun. Scientists suspect that this X-ray activity is somehow related to its advanced stage of evolution called core helium burning. During this stage, the core of the star is very hot (more than a hundred million degrees Celsius) and converting helium to carbon via nuclear fusion reactions.

Using the theory of how stars evolve, we can reconstruct the history of Beta Ceti, a star with a mass of about 3 Suns. Over the first billion years of its existence, Beta Ceti was powered by nuclear fusion reactions converting hydrogen to helium in the core.

After the hydrogen in the core was exhausted, the central region of the star contracted until hydrogen gas around the helium core became hot and dense enough for hydrogen fusion reactions to ignite there. This powerful new energy source caused the outer regions of the star to expand greatly and cool. At this point Beta Ceti became a red giant. During the red giant phase, Beta Ceti would have been a very weak X-ray source.

After about 10 million years, the core of the star contracted and heated to more than 100 million degrees, enabling helium fusion reactions to occur there. In this core helium burning stage, which will last 100 million years or more, the overall diameter of the star has shrunk to about 20 times that of the Sun and the surface temperature has increased, so it is no longer a red giant star.

Original Source: Chandra News Release

Posted on by Fraser Cain

Spirit Completes a Year on Mars

NASA lit a birthday candle today for its twin Mars Exploration Rovers, Spirit and Opportunity. The Spirit rover begins its second year on Mars investigating puzzling rocks unlike any found earlier.

The rovers successfully completed their three-month primary missions in April. They astound even their designers with how well they continue operating. The unanticipated longevity is allowing both rovers to reach additional destinations and to keep making discoveries. Spirit landed on Jan. 3 and Opportunity Jan. 24, 2004, respectively.

“You could have cut the tension here with a knife the night Spirit landed,” said NASA Administrator Sean O’Keefe. “Just remembering the uncertainty involved with the landing emphasizes how exciting it is for all of us, since the rovers are still actively exploring. The rovers created an amazing amount of public interest and have certainly helped advance the Vision for Space Exploration,” he said. The twin Mars explorers have drawn the most hits to NASA Web sites – – more than 9 billion in 2004.

Dr. Charles Elachi, director of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., said, “Little did we know a year ago that we’d be celebrating a year of roving on Mars. The success of both rovers is tribute to hundreds of talented men and women who have put their knowledge and labor into this team effort.”

“The rovers are both in amazingly good shape for their age,” said JPL’s Jim Erickson, rover project manager. “The twins sailed through the worst of the martian winter with flying colors, and spring is coming. Both rovers are in strong positions to continue exploring, but we can’t give you any guarantees.”

Opportunity is driving toward the heat shield that protected it during descent through the martian atmosphere. Rover team members hope to determine how deeply the atmospheric friction charred the protective layer. “With luck, our observations may help to improve our ability to deliver future vehicles to the surface of other planets,” Erickson said.

Spirit is exploring the Columbia Hills within the Gusev Crater. “In December, we discovered a completely new type of rock in Columbia Hills, unlike anything seen before on Mars,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers’ science payloads.

Jumbled textures of specimens dubbed “Wishstone” and “Wishing Well” look like the product of an explosion, perhaps from a volcano or a meteor impact. These rocks are much richer in phosphorus than any other known Mars rocks. “Some ways of making phosphates involve water; others do not,” Squyres said. “We want to look at more of these rocks to see if we can distinguish between those possible histories.”

NASA’s next Mars mission, the Mars Reconnaissance Orbiter, is due to launch in August. “As great as the past year has been, Mars launch opportunities come along like clockwork every 26 months,” said Dr. Firouz Naderi of JPL, manager of NASA’s Mars Exploration Program. “At every one of them in the foreseeable future, we intend to go to Mars, building upon the findings by the rovers.”

NASA Chief Scientist Dr. Jim Garvin said, “Mars lures us to explore its mysteries. It is the most Earth-like of our sister planets, and many believe it may hold clues to whether life ever existed or even originated beyond Earth. The rovers have shown us Mars had persistently wet, possibly life-sustaining environments. Beyond their own profound discoveries, the rovers have advanced our step-by- step program for examining Mars. We will continue to explore Mars robotically, and eventually with human explorers.”

Images and additional information about the rovers and their discoveries are available on the Internet at http://www.nasa.gov/vision/universe/solarsystem/mer_main.html and http://marsrovers.jpl.nasa.gov/home/index.html.

JPL has managed the Mars Exploration Rover project since it began in 2000. JPL is a division of the California Institute of Technology in Pasadena.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Close Up Images of Iapetus

NASA’s Cassini spacecraft successfully flew by Saturn’s moon Iapetus at a distance of 123,400 kilometers (76,700 miles) on Friday, Dec. 31. NASA’s Deep Space Network tracking station in Goldstone, Calif., received the signal and science data that day beginning at 11:47 p.m. Pacific Standard Time.

Iapetus is a world of sharp contrasts. The leading hemisphere is as dark as a freshly-tarred street, and the white, trailing hemisphere resembles freshly-fallen snow.

Friday’s flyby was the first close encounter of Iapetus during the four-year Cassini tour. The second and final close flyby of Iapetus is scheduled for 2007. Next up for Cassini is communications support for the European Space Agency’s Huygens probe during its descent to Titan on Jan. 14.

The Huygens probe successfully detached from the Cassini orbiter on Dec. 24. The data gathered during the descent through Titan’s atmosphere will be transmitted from the probe to the Cassini orbiter. Afterward, Cassini will point its antenna to Earth and relay the data through NASA’s Deep Space Network to NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and on to the European Space Agency’s Space Operations Center in Darmstadt, Germany, which serves as the operations center for the Huygens probe mission. Two of the instruments on the probe — the camera system and the gas chromatograph/mass spectrometer — were provided by NASA.

Raw images from the Iapetus flyby are available at: http://saturn.jpl.nasa.gov/multimedia/images/raw. More information on the Cassini-Huygens mission is available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The European Space Agency built and managed the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Starbirth in NGC 6946

Like the annual New Year?s fireworks display, astronomers at Gemini Observatory are ushering in 2005 with a striking image that dazzles the eye with stellar pyrotechnics.

In the image, the face-on spiral galaxy NGC 6946 is ablaze with colorful galactic fireworks fueled by the births and deaths of multitudes of brilliant, massive stars. Astronomers suspect that massive stellar giants have been ending their lives in supernova explosions throughout NGC 6946 in rapid-fire fashion for tens of millions of years.

?In order to sustain this rate of supernova activity, massive, quickly evolving stars must form or be born at an equally rapid rate in NGC 6946,? said Gemini North Associate Director, Jean-Ren? Roy. ?Its stars are exploding like a string of firecrackers!?

Astronomers speculate that if just a million years of this galaxy?s history were compressed into a time-lapse movie lasting a few seconds, there would be nearly constant outbursts of light as new stars flare into view, while old ones expire in spectacular explosions. Over the past century, eight supernovae have exploded in the arms of this stellar metropolis, occurring in 1917, 1939, 1948, 1968, 1969, 1980, 2002, and 2004. This makes NGC 6946 the most prolific known galaxy for supernovae during the past 100 years.

By comparison, the average rate for such catastrophic stellar outbursts in the Milky Way is about one per century, and only four have been recorded over the last thousand years. The last known supernova went off in our galaxy in the constellation Ophiuchus in 1604.

Yet, it is the ubiquitous occurrence of starbirth throughout NGC 6946 and not its supernovae that lend this galaxy its blazingly colorful appearance. For reasons not completely understood, it experiences a much higher rate of star formation than all the large galaxies in our local neighborhood. The prodigious output of stellar nurseries in this galactic neighbor eventually leads to accelerated numbers of supernova explosions.

Starbirth regions exist in most galaxies, particularly in spirals, and are obvious as clouds of predominantly hydrogen gas called H II regions. These areas coalesce over millions of years to form stars. Young, hot, massive stars formed in these regions emit copious amounts of ultraviolet radiation, which strip the electrons from hydrogen atoms in which they are embedded. When these ionized hydrogen atoms re-associate with electrons they radiate in a deep red color (at a wavelength of 656.3 nanometers) as the electrons transition back to lower energy levels.

This Gemini image of NGC 6946 utilizes a selective filter specifically designed to detect the radiation emanating from the starbirth regions. Additional filters help to distinguish other details in the galaxy, including clusters of massive blue stars, dust lanes, and a yellowish core where older more evolved stars dominate.

NGC 6946 lies between 10 and 20 million light-years away on the border between the constellations of Cepheus and Cygnus, and was discovered by Sir William Herschel (1738-1822) on September 9, 1798. It continues to fascinate astronomers, who estimate that it contains about half as many stars as the Milky Way. They often use it to study and characterize the evolution of massive stars and the properties of interstellar gas. As viewed in the new Gemini optical image, we see only the ?tip of the iceberg? of this galaxy. Its optical angular diameter is about 13 arcminutes, but viewed at radio wavelength at the frequency of neutral hydrogen (1420 Mhz or 21-cm line), it extends considerably more than the angular diameter of the Moon.

Original Source: Gemini News Release

Posted on by Fraser Cain

What’s Up This Week – Jan 3 – Jan 9, 2005

Monday, January 3 – For those of you who were brave enough to fight the cold this morning to look for the annual Quandrantid meteor shower? Bravo! But if bad skies or arctic temperatures kept you from viewing, you still have another opportunity because this unusual meteor shower peaks over a period of two days.

The Quadrantid meteor shower has been known to be an incredibly concentrated display – at times producing between 50 to 120 meteors in the northern hemisphere. It is infrequently observed simply because of low temperatures in the north and bad positioning in the south. Another reason we do not known much about this shower is the short period of time that it is active. The peak can only last a few hours! The meteoroid stream itself is vast, but very accurate predictions are difficult thanks to complex streams perturbed by Jupiter’s gravity. The precise source of the Quadrantid meteor wasn’t even discovered until December 2003! Just slightly over a year ago, Peter Jenniskens of NASA Ames Research Center found evidence that tied the Quadrantids to an extinct comet now known as asteroid 2003 EH1. Historical observations reveal this comet was visible some 500 years ago, but may have suffered some type of impact that caused it to break up. Because we hit this “debris stream” at a perpendicular angle, we are “in and out” rather quickly – making precise calculations difficult at best.

The Quadrantids are named for a constellation that no longer exists on modern star atlases – Quadrans Muralis. In 1922, the International Astronomical Society removed it (along with several others) from the overburdened sky maps leaving only 88 officially designated constellations. So where do you look? The accepted radiant for the Quadrantids has now been assigned to Bootes, but the stream kept its original name to help distinguish it from another annual January shower – the Bootids. Even though the constellation might be gone, your chances are still good of catching one of these “frosty meteors”! The hours after local midnight will be best as we move into January 4. Although the waning Moon will decrease the number you may see, be sure to watch for “colors” in the display. As meteors burn up in our atmosphere, they produce colors thanks to their chemical spectra and the Quadrantids are known to range from blue to green. Best of luck!

Tuesday, January 4 – Heads up for Africa and southwestern Australia! It’s your turn for an astronomical event as the Moon will occult Jupiter for your location in the early morning hours. (see? i haven’t forgotten you!) Timing is absolutely critical for this type of observation, so please visit this IOTA page for the precise path and list of times for your area. For those of us who will only see the Moon and Jupiter separated by less than 7 degrees, we wish you clear skies!

For sky watchers around 40 degrees north, this morning will mark the latest sunrise of the year. Why not take advantage this morning before beginning your busy day and have a look at the simple beauty of the ecliptic plane? To the east and down low on the horizon will be Mercury and Venus, above them (about 17 degrees to the west) will be tiny Mars. Almost overhead, and just slightly south will be Jupiter and west of it will be the Moon. Continue your visual journey to the far west as Saturn completes this lovely arc.

With plenty of time to spare before the Moon rises tonight, let’s try for a new Messier object. Located slightly more than 2 degrees northeast of Zeta Orionis and right on the celestial equator is a delightful area of bright nebula known as the M78 (NGC 2068). Often over-looked in favour of “the Great Orion Nebula”, this 8th magnitude diffuse area is easily captured with small scopes. Discovered by Mechain in 1789, the M78 is part of the vast complex of nebulae and star birth that comprise the Orion region. Fueled by twin magnitude 10 stars, the nebula almost appears to the eye to resemble a “double comet”. Upon close scrutiny, observers will note two lobes separated by a dark band of dust and each lobe bears its own designation – NGC 2067 to the north and NGC 2064 to the south. While studying, you will notice the entire area is surrounded by a region of absorption, making the borders appear almost starless! The M78 itself is filled with T Tauri type stars… But we’ll explore why these variables are incredible as we examine their prototype later this week.

Wednesday, January 5 – Tonight let’s take a journey just a breath above Zeta Tauri and spend some time with the most famous supernova remnant of all – the M1. Factually, we know the “Crab Nebula” to be the remains of an exploded star recorded by the Chinese in 1054. We know it to be a rapid expanding cloud of gas moving outward at a rate of 1,000 km per second, just as we understand there is a pulsar in the center. We also know it as first recorded by John Bevis in 1758, and then later cataloged as the beginning Messier object – penned by Charles himself some 27 years later to avoid confusion while searching for comets. We see it revealed beautifully in timed exposure photographs, its glory captured forever through the eye of the camera — but have you ever really taken the time to truly study the M1? Then you just may surprise yourself…

In a small telescope, the “Crab Nebula” might seem to be a disappointment – but do not just glance at it and move on. There is a very strange quality to the light which reaches your eye, even though at first it may just appear as a vague, misty patch. To small aperture and well-adjusted eyes, the M1 will appear to have “living” qualities – a sense of movement in something that should be motionless. This aroused my curiosity to study and by using a 12.5″ scope, the reasons become very clear to me as the full dimensions of the M1 “came to light”.

The “Crab” Nebula holds true to so many other spectroscopic studies I have enjoyed over the years. The concept of differing light waves crossing over one another and canceling each other out – with each trough and crest revealing differing details to the eye – is never more apparent than during study. To truly watch the M1 is to at one moment see a “cloud” of nebulosity, the next a broad ribbon or filament, and at another a dark patch. When skies are perfectly stable you may see an embedded star, and it is possible to see six such stars. It is sometimes difficult to “see” what others understand through experience, but it can be explained. It is more than just the pulsar at its center teasing the eye, it is the “living” quality of which I speak -TRUE astronomy in action. There is so much information being fed into the brain by the eye!

I believe we are all born with the ability to see spectral qualities, but they just go undeveloped. From ionization to polarization – our eye and brain are capable of seeing to the edge of infra-red and ultra-violet. How about magnetism? We can interpret magnetism visually – one only has to view the “Wilson Effect” in solar studies to understand. What of the spinning neutron star at its heart? We’ve known since 1969 the M1 produces a “visual” pulsar effect! We are now aware that about once every five minutes, changes occuring in the neutron star’s pulsation effect the amount of polarization, causing the light waves to sweep around like a giant “cosmic lighthouse” and flash across our eyes. For now, l’ll get down of my “physics” soapbox and just let it suffice to say that the M1 is much, much more than just another Messier. Capture it tonight!!

Thursday, January 6 – Since we’ve studied the “death” of a star, why not take the time tonight to discover the “birth” of one? Our journey will start by identifying Aldeberan (Alpha Tauri) and moving northwest to bright Epsilon. Hop 1.8 degrees west and slightly to the north for an incredibly unusual variable star – T Tauri.

Discovered by J.R. Hind in October 1852, T Tauri and its accompanying nebula, NGC 1555 set the stage for discovery with a pre-main sequence variable star. Hind reported the nebula, but also noted that no catalog listed such an object in that position. His observance also included a 10th magnitude uncharted star and he surmised that the star in question was a variable. On either account, Hind was right and both were followed by astronomers for several years until they began to fade in 1861. By 1868, neither could be seen and it wasn’t until 1890 that the pair was re-discovered by E.E. Barnard and S.W. Burnham. Five years later? They vanished again.

T Tauri is the prototype of this particular class of variable stars and is itself totally unpredictable. In a period as short as a few weeks, it might move from magnitude 9 to 13 and other times remain constant for months on end. It is about average to our own Sun in temperature and mass – and its spectral signature is very similar to Sol’s chromosphere – but the resemblance ends there. T Tauri is a star in the initial stages of birth!

So what exactly are T Tauri stars? They may be very similar in ways to our own Sun but they are far more luminous and rotate much faster. For the most part, they are located near molecular clouds and produce massive outflows of this material in accretion as evidenced by the variable nebula, NGC 1555. Like Sol, they produce X-ray emissions, but a thousand times more strong! We know they are young because of the spectra – high in lithium – which is not present at low core temperatures. T Tauri has not reached the point yet where proton to proton fusion is possible! Perhaps in a few million years T Tauri will ignite in nuclear fusion and the accretion disk become a solar system. And just think! We’re lucky enough to see them both…

Friday, January 7 – For mid-northern latitudes, this morning will be the last chance to see the crescent Moon (gosh, aren’t you crushed?) before it goes new. But for those living in northwestern America, the treat will be extra special as the Moon will occult Antares! Be sure to visit IOTA for precise times and locations.

Are your ready for a real weekend treat? Then look no further than the night sky above as Comet Machholz will be putting on one of the best shows of the year as it appears around 2 degrees west of the Plieades star cluster!

Near the ecliptic, and with a rough visual magnitude of slightly less than 2, the Plieades (M45) will appear brighter than Comet Machholz – but current information suggests that C/2004 Q2 will have achieved 4th magnitude by that time – making both easy unaided-eye objects. Average binoculars span a field of around 4 degrees, so both objects should fill the field of view! While watching, take the time to practice with size, distance and magnitude observations. The M45 spans approximately 1.2 degrees of sky – how does the size of the comet’s coma compare? Since the two are around 2 degrees apart, how long does the tail seem to span? The brightest of the major stars in the Plieades is 2.8 and the dimmest approximately 5.6 – by defocusing, how bright does Comet Machholz nucleus appear in comparison? You know what direction the M45 is from Machholz, which way does the twin tail appear to go?

Of course, you needn’t truly worry about any of this just to enjoy the view! I’ll race you there…

Saturday, January 8 – So are you ready for a real challenge? Then take advantage of dark sky time to head toward Orion. Tonight our aim is toward a single star – but there is much more hiding there than just a point of light!

Our goal is the eastern-most star in the “belt”, Zeta Orionis, or better known as Alnitak. At a distance of some 1600 light years away, this 1.7 magnitude beauty contains many surprises – the first being that Zeta is a triple system. Fine optics, high power and steady skies will be needed to reveal this challenge! Want more? Then look about 15′ east and you will see that Alnitak resides in a fantastic field of nebulosity which is illuminated by our tripartite star. The NGC2024 is an outstanding area of emission that holds a rough magnitude of 8 – viewable in small scopes but will require dark sky. So what’s so exciting about a fuzzy patch? Then look again, for this beauty is known as the “Flame”! Larger telescopes will deeply appreciate this nebula’s many dark lanes, bright filaments and unique shape! Still not enough? Then break out the big scopes and put Zeta out of the field of view to the north at high power and allow your eyes to re-adjust. When you look again, you will see a long, faded ribbon of nebulosity called IC434 to the south of Zeta that stretches for over a degree. The eastern edge of the “ribbon” is very bright and mists away to the west… But hold your breath and look almost directly in the center. See that dark notch with two faint stars south of it? You have now located one of the most famous of the Barnard dark nebula – B33.

You may exhale now. The B33 is also known as the “Horsehead Nebula”. The “Horsehead” is a very tough visual object – the classic chess piece shape only seen in photographs – but those of you who have large aperture can see a dark “node” that is improved with a filter. The B33 itself is nothing more than a small area comsically (about 1 light year in expanse) of obscuring dark dust, non-luminous gases, and dark matter – but what an incredible shape! If you do not succeed at first attempt? Do not give up. The “Horsehead” is one of the most challenging objects in the sky and has been observed with apertures as small as 150mm. Keep trying! This just might be your lucky “Knight”…

Sunday, January 9 – Tonight’s destination will be within our own solar system, but with good reason! As we know, all the orbits of the planets are tilted relative to our own Earth’s orbit. This means that each time a planet completes an orbit around the Sun, it must pass over our own orbital plane twice. One time it will move from above Earth’s orbit to below, and the next it will go in the opposite direction. Tonight, Saturn will cross Earth’s orbital plane from below to above and this action of passing is what is astronomically known as the “ascending node”. It is rather special because it will be another 29 years before Saturn completely orbits the Sun and achieves the “ascending node” again!

So what does that mean to those wishing to view Saturn tonight? Not much other than it is a “cool” astronomy fact. The best time to view Saturn is at opposition which won’t occur for about another year. The most interesting part about watching Saturn right now is the ring system. Like our Earth, Saturn tilts on its axis. Since the ring system is equatorial, our best views of the rings themselves come when Saturn is highly inclined. As luck would have it, Saturn is well placed right now for just such viewing. Right now, it’s saturnian winter for the Ring King’s northern hemisphere, so get thee out there an explore! Small telescopes at high power can make out the pencil slim line of the Cassini Division on a stable night, while larger telescopes can easily spot other ring divisions. Be sure to watch for Saturn’s many moons as well. Titan is easily visible to the smallest of scopes and even a 114mm can reveal as many as four others. Enjoy it tonight!

Is it gone yet? Yes! New Moon week is about to begin, so expect some more challenging objects for veteran observers next time. For those just beginning? Don’t worry. There will be plenty for you to explore as well! I would like to thank all of you who take time to write – you’ll never know how much I appreciate it! (and earthlink users? please check your rejected mail for answers to your questions.) Until next time, ask for the Moon but keep reaching for the stars!

Light speed… ~Tammy Plotner

Posted on by Fraser Cain

Cassini’s Route Past Iapetus

NASA’s Cassini spacecraft is set to cap off 2004 with an encounter of Saturn’s ying-yang moon Iapetus (eye-APP-eh-tuss) on New Year’s Eve.

This is Cassini’s closest pass yet by one of Saturn?s smaller icy satellites since its arrival around the ringed giant on June 30 of this year. The next close flyby of Iapetus is not until 2007.

Iapetus is a world of sharp contrasts. The leading hemisphere is as dark as a freshly-tarred street, and the white, trailing hemisphere resembles freshly-fallen snow.

Cassini will fly by the two-toned moon at a distance of approximately 123,400 kilometers (76,700 miles) on Friday, Dec. 31. This flyby brings to an end a year of major accomplishments and rings in what promises to be a year filled with new discoveries about Saturn and its moons.

“I can think of no better way than this to wrap up what has been a whirlwind year,” said Robert T. Mitchell, program manager for the Cassini mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “The new year offers new opportunities, and 2005 will be the year of the icy satellites.”

In 2005 Cassini will have 13 targeted encounters with five of Saturn’s moons. “We have 43 close flybys of Titan still ahead of us during the four-year tour. Next year, eight of our 13 close flybys will be of Titan. We will also have a number of more distant flybys of the icy satellites, and let’s not forget Saturn and the rings each time we come around,” said Mitchell.

With a diameter of about 1,400 kilometers (890 miles), Iapetus is Saturn’s third largest moon. It was discovered by Jean-Dominique Cassini in 1672. It was Cassini, for whom the Cassini-Huygens mission is named, who correctly deduced that one side of Iapetus was dark, while the other was white.

Scientists still do not agree on whether the dark material originated from an outside source or was created from Iapetus’ own interior. One scenario for the outside deposit of material would involve dark particles being ejected from Saturn?s little moon Phoebe and drifting inward to coat Iapetus. The major problem with this model is that the dark material on Iapetus is redder than Phoebe, although the material could have undergone chemical changes that made it redder after its expulsion from Phoebe. One observation lending credence to the theory of an internal origin is the concentration of material on crater floors, which implies that something is filling in the craters. In one model proposed by scientists, methane could erupt from the interior and then become darkened by ultraviolet radiation.

Iapetus is odd in other respects. It is the only large Saturn moon in a highly inclined orbit, one that takes it far above and below the plane in which the rings and most of the moons orbit. It is less dense than objects of similar brightness, which implies it has a higher fraction of ice or possibly methane or ammonia in its interior.

The last look at Iapetus was by NASA’s Voyager 1 and 2 spacecraft in 1980 and 1981. The Cassini images will be the highest resolution images yet of this mysterious moon. The Iapetus flyby by Cassini follows the successful release of the Huygens probe on December 24.

More information on the Cassini-Huygens mission is available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The European Space Agency built and managed the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments.

Cassini spacecraft targeted satellite encounters for 2005:

Titan: January 14, 2005
Titan: February 15, 2005
Enceladus: March 9, 2005
Titan: March 31, 2005
Titan: April 16, 2005
Enceladus: July 14, 2005
Titan: August 22, 2005
Titan: September 7, 2005
Hyperion: September 26, 2005
Dione: October 11, 2005
Titan: October 28, 2005
Rhea: November 26, 2005
Titan: December 26, 2005

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Your Interview with Dr. Jean-Pierre Lebreton

Just how dense is Titan’s atmosphere expected to be, and how did that influence the design of the probe? – Kepesk

The atmosphere of Titan is denser and thicker than that of the Earth. The surface pressure is 1.5 times that on Earth (1500 mbar). But because Titan gravity is 1/6 of Earth’s, the atmosphere is much more expanded. Huygens will brake at about 300 km altitude, while Earth re-entry vehicles brake at about 60 km altitude.

The probe was designed to brake as high as possible for allowing in-situ sampling of the atmosphere as high as possible (about 165 km). It required a large heat-shield.

The heat-shield design was influenced by the presence of methane in the atmosphere. Methane and nitrogen break apart in the shock layer that forms in front of the probe during the hypersonic entry and form the CN radical which is a strong emitter of violet radiation (during the entry, Huygens radiates as much as 1000 sun for about 30 sec). CN radiates a lot of heat on the heat-shield. The amount of radiation (heat flux) on Huygens heat shield is 3 to 4 times higher than if we would enter in a pure nitrogen atmosphere.

How did Titan “collect” so much organic material and get such a dense atmosphere? Did Titan “collect” the stuff or was the moon lucky and manage not to lose it? – baselle

This is a fundamental question. Answering it is a major scientific objective of the Cassini-Huygens mission. Most (if not all) of the organic matter in Titan’s atmosphere and on the surface comes from the chemical processing of methane. The origin of methane is one of the big mysteries that Huygens should help to solve.

What design considerations were made on the probe to help ensure it would survive a trip to Saturn that took it on flybys to a few other planets along the way? – dave_f

The main design considerations for Huygens long trip to Saturn were to ensure that the temperature of its batteries would be kept cool enough. Huygens is protected by a multi-layer insulation thermal blanket and protected from the sun by the orbiter high-gain antenna until we reached Jupiter. Regular (bi-annual) activations of Huygens during a few hours were designed to monitor its health and calibration and to activate movable instrument mechanisms for their maintenance.

Survived landing will be a bonus, not the goal, with this in mind, was there anything other than timing and synchronicity with the orbiter considered when choosing a “landing” site? – tiderider

Huygens is not a lander. So I prefer to talk about impact or touchdown site. The impact site was not specifically chosen. The main drivers were: i) the entry angle in the atmosphere, ii) the need to descend in the sunlit side of Titan, iii) a low to medium latitude descent, but away from the equator for best wind measurements, and iv) an optimized geometry for the radio link with the orbiter.

Supposing that remarkable observations where recorded by Huygens, how could such observations contribute to our understanding of the solar system evolution? – Keemah

The detailed in-situ measurements by Huygens will be combined with the several-year global observations by the Cassini orbiter during its planned 45+ (more if the mission is extended) Titan flybys in order to better understand the weather on Titan, the chemical composition of the atmosphere, the origin and fate of the methane. In-situ isotopic measurements are a key for understanding the origin and evolution of Titan’s atmosphere. Understanding why Titan has a thick atmosphere (the only moon in the solar system to have a substantial atmosphere) will allow testing theories of planetary formation and evolution.

Are there some atmospheric (or even surface) conditions expected to disturb data transmission from Huygens to Cassini? – Lamahe

The atmosphere is transparent to radio communication between Huygens and Cassini (at 2 GHz). Too large a swing under the parachute may disturb the communication for a few seconds but Huygens will transmit on two radio channels. Key data are transmitted on the two channels but delayed by 6 sec on one of the two channels. This delay will allow all important data to be recovered if the link is interrupted for a short time.

If all goes well, how soon will detailed information about what did the probe observe be made available to the public? Is there a period when certain scientists have exclusive access? – antoniseb

Information will be made available to the public within hours after the data are received on earth on 14th January. Scientists will make every effort to make as much information as possible to the public. But scientists will also publish their research results in scientific literature within months. All Huygens data will be made available to the wide scientific community and to the public at large through ESA and NASA Planetary data archives in 2006.

What advice would you give someone who’s willing to work in space research? – Ola D.

You need to get a good education is mathematics, physics and chemistry, but also in literature and history of sciences in order to be able to communicate your research results to the public. You also need to be motivated to embrace a research career as jobs are difficult to get and not always well paid. If you want to undertake planetary research you need patience and to be unselfish. It took more than twenty years to get to Saturn from mission idea to the arrival. It will take years and decades to analyze all the data that will be returned by Cassini-Huygens. A mission such as Cassini-Huygens goes across generations. Cassini-like missions to Uranus and Neptune will take longer. But it is so exciting to be involved in such voyages that I would encourage all school boys and girls to study sciences and take a chance. It’s worth it. One more piece of advice. Cassini-Huygens is a true example of highly successful international collaboration. Learn a few languages as it will help to enjoy your trips abroad and best appreciate the multi-cultural environment you will work in as I am convinced that planetary exploration must be undertaken through multi-national collaborations.