MESSENGER Looks Back at the Earth and Moon

Earth and Moon from 114 Million Miles.Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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A new image to add to the family photo album! The MESSENGER spacecraft is working its way to enter orbit around Mercury in March of 2011, and while wending its way, took this image of the Earth and Moon, visible in the lower left. When the image was taken in May 2010, MESSENGER was 183 million kilometers (114 million miles) away from Earth. For context, the average separation between the Earth and the Sun is about 150 million kilometers (93 million miles). It’s a thought provoking image (every one of us is in that image!), just like other Earth-Moon photos — Fraser put together a gallery of Earth-Moon images from other worlds, and this one will have to be added. But this image was taken not just for the aesthetics.

This image was taken as part of MESSENGER’s campaign to search for vulcanoids, small rocky objects hypothesized to exist in orbits between Mercury and the Sun. Though no vulcanoids have yet been detected, the MESSENGER spacecraft is in a unique position to look for smaller and fainter vulcanoids than has ever before been possible. MESSENGER’s vulcanoid searches occur near perihelion passages, when the spacecraft’s orbit brings it closest to the Sun. August 17, 2010 was another such perihelion, so if MESSENGER was successful in finding any tiny asteroids lurking close to the Sun, we may hear about it soon.

Source: MESSENGER

Where In The Universe #115

It’s time once again for another Where In The Universe Challenge. Test your visual knowledge of the cosmos by naming where in the Universe this image was taken and give yourself extra points if you can name the spacecraft/telescope responsible for this picture. Post your guesses in the comments section, and check back on later at this same post to find the answer. To make this challenge fun for everyone, please don’t include links or extensive explanations with your answer. Good luck!

I have to admit, the “Patrick Stewart” answer made me laugh out loud, but really, (as most of you guessed) this is an ultraviolet image of Venus’ clouds as seen by the Hubble Space Telescope’s Wide-Field/Planetary Camera 2 taken on January 24 1995, when Venus was at a distance of 70.6 million miles (113.6 million kilometers) from Earth.

You can read more about this image, including why there is a “Y”-shaped pattern in the clouds, at this webpage from NASA’s Goddard Spaceflight Center.

Contest: Win New Book About the Sloan Digital Sky Survey


UPDATE: The winner of the book is Irfaan Hamdulay from Cape Town, South Africa. Congrats!

A new giveaway for Universe Today readers! We’ve just reviewed a new book about the Sloan Digital Sky Survey called “A Grand and Bold Thing” by Ann Finkbeiner. It’s a great read about a great and visionary project — so how would you like to have your very own copy? Just send an email to Universe Today with “SDSS” in the subject line, and we’ll choose a winner. Deadline for entry is Monday, August 23, 2010 at 12 noon PDT.

By the way, we want to congratulate the winner of the Lunar Science Swag, Jesse Rogerson from Ontario, Canada!

The Sloan Digital Sky Survey: “A Grand and Bold Thing”


If you do a search of articles on Universe Today, you’ll find that a large number of our posts reference the Sloan Digital Sky Survey. SDSS is a comprehensive survey to map the sky, using a dedicated 2.5 meter telescope equipped with a 125- megapixel digital camera and spectrographs. Since 2000, SDSS has created terabytes of data that include thousands of deep, multi-color images, covering more than one-quarter of the sky. SDSS is literally changing the way astronomers do their work, and represents a thousand-fold increase in the total amount of data that astronomers have collected to date. In a new book, “A Grand and Bold Thing; An Extraordinary New Map of the Universe Ushering in a New Era of Discovery,” science journalist Ann Finkbeiner tells the story of how SDSS came about (frighteningly, the survey almost didn’t happen), delving into some of the discoveries made as a result of this survey, and sharing how even armchair astronomers are now probing the far reaches of the Universe with SDSS.

SDSS has measured the distances to nearly one million galaxies and over 100,000 quasars to create the largest ever three-dimensional maps of cosmic structure. It also spawned one of our favorite citizen science projects: Galaxy Zoo.

For three years, Ann Finkbeiner researched and interviewed astronomers to get the story behind SDSS, to tell the little-known story of this grand project, and how it soon grew into a far vaster undertaking than founder Jim Gunn could have imagined. The book is extremely readable, and Finkbeiner captures the personalities who brought the project to life. If you thought Earth-based observing was passe, this book will make you re-think the future of astronomy.

Finkbeiner is a freelance science writer who has been covering astronomy and cosmology for over two decades. She has written feature articles for Science, Sky & Telescope, Astronomy, and more, with columns for USA Today, and Defense Technology International. She is co-author of The Guide to Living with HIV Infection (Johns Hopkins University Press, 1991; sixth edition, 2006), which won the American Medical Writers Association book award. She is also author of “After the Death of a Child,” and “The Jasons,” which won the American Institute of Physics’ Science Writing Award in 2008.

Below is a Q & A with Finkbeiner about “A Grand and Bold Thing.”

Q: What made you first want to write this book?
A: I was finishing a magazine article about the Sloan Digital Sky Survey just as I was beginning the interviews for a book—The Jasons—for which no one at all wanted to talk to me. But the Sloanies I was interviewing were so happy about what they were doing, so intense about it all, and so open (they even showed me their gazillion archived emails) that writing a book about them felt like it would be a blessed relief, like leaving boot camp and going to a good block party.

I was writing the magazine article in the first place because I’d attended a talk by Jim Gunn at Johns Hopkins, and while I listened, I realized I hadn’t heard any news from him for a long time. So I afterward, I asked him why he’d gone off radar. He told me he’d been working on getting a survey going, using a little 2.5 meter telescope, and I wasn’t impressed. I thought it was an odd use of his splendid capabilities. I was impressed later, though, when he stayed off radar and I found out that other excellent scientists were doing the same. I started wondering why they were giving up their careers for a sky survey.

Q: Has perception of the project changed from the time you first started writing about it until now?
A: Between the time I first heard about it—in the late 1990’s—and the present, the perception of the project changed dramatically: today, it’s hard to overstate its importance. But astronomers’ early reactions to the survey were what mine had been: Little telescope. Not spectacular resolution. Can’t go very deep in the past. Astronomers who knew the value of a survey and Jim’s reputation for building nearly-perfect instruments were quicker to see the potential, but the project’s many, many management problems led to the community taking pot shots at the Sloanies. Then when funding agencies started refusing to give astronomers money because the Sloan was going to do their pet projects better than they would, Sloan became a dirty word. Now, astronomers say it changed the way they do their work.

Q: What do you think have been the most important benefits of the Sloan Survey’s completion?
A: The Sloan was, and still is, the only systematic, beautifully-calibrated survey of the sky and everything in it. And it’s the first survey to be digital. Astronomy before Sloan was photographic, meaning you were at a rich university that owned a telescope, you decided which objects in the sky you liked and took photographs of them, and kept them for yourself. If you wanted to use the only survey of the sky, you bought expensive photographs of it. After the Sloan, you download the objects you want to study onto your computer for free. So whether you’re an astronomer or a regular person, you can study anything you want to with some of the most trustworthy data going. And if you don’t want to learn astronomy jargon and query languages, you can go to GalaxyZoo.com and join the 300,000 people doing astronomy on the Internet using this data. The Sloan has democratized astronomy. It’s made “citizen science” real. And it’s about to become redundant because it triggered a population of other newer, bigger surveys.

Q: What do you think the story of the Sloan Survey tells us about current cosmological thought?
A: Before Sloan, cosmology was seen as a fluffy science: the universe is big, distant, and hard to observe, so the phrase “precision cosmology” would have been an in-joke. But Sloan’s data is so comprehensive and exquisite that precision cosmology is now the norm.

Before the Sloan, cosmology was fractured into many fields whose relation to each other wasn’t obvious and wasn’t being studied. Sloan found all kinds of things in all areas of astronomy: asteroids in whole families, stars that had only been theories, star streams around the Milky Way, the era when quasars were born, the evolution of galaxies, the structure of the universe on the large scale, and compelling evidence for dark energy. So after the Sloan, cosmologists began seeing the universe as a whole, as a single system with parts that interact and evolve.

Q: Work like this costs an enormous amount of money, but doesn’t yield the sort of practical results the average American can see. What is the best argument to continue funding science like this?
A: The main Sloan survey cost $85 million over 10 or 15 years. In the realm of government budgets, that’s spare change. It cost so little partly because the scientists gave their time for free—they had university salaries already. And since this free time came at the expense of their own research and personal reputations, they’re a case study in altruism. In addition, the universe is mankind’s most fundamental context; and astronomy and cosmology have, I think, some of the appeal of philosophy and religion. Put scientific intelligence together with altruism and questions of origin and place in the universe, throw in beautiful pictures, and I’d give it money in a minute.

Q: There are a lot of good stories behind the making of the Survey. What are some of your personal favorites?
A: My all-time favorite is Galaxy Zoo, which started when a couple of Sloanies needed to know which galaxies were spirals, which were ellipticals, and which were irregular. But Sloan had a million galaxies, which is a lot for any human to sort through: computers are no good at identifying shapes, humans are superb at it. So the Sloanies put the million galaxies on the internet, asked for help, and within a day, their computer server melted. There are now 300,000 Galaxy Zooites of all ages, all levels of education, from all over the world, and they’ve gone way beyond classifying shapes. Hanny van Arkel, a Dutch primary school teacher, found a strange blue object the Zooites called Hanny’s Voorwerp, and after followups with xray, ultraviolet, and radio telescopes (not to mention the Hubble Space Telescope), the Voorwerp turned out to be a place in an enormous cloud of gas which was being hit by a hard xray jet from a galactic-sized black hole. Zooites also found a new kind of greenish, round galaxy, and then found enough of them that they’re now officially called Green Pea galaxies. Green Peas turn out to be small, nearby, previously unknown galaxies in which stars are being born at a furious rate. Then Zooites went off and taught themselves serious astronomical techniques and began collecting and studying irregular galaxies; astronomers knew of 161 irregulars, the Zooites found 19,000 of them and called their project, Do It Ourselves.

I also love Jim Gunn’s professional trajectory from fame to invisibility, and while invisible, his fight-starting and progress-impeding insistence on doing everything as well as it can possibly be done. When Jim started the Sloan, he was extremely famous and highly respected. He walked away from his own research and spent the next 30 (he’s still doing it) years first putting together the collaboration, then building the camera, while also overseeing and micromanaging every detail of every piece of hardware, software, and politics. He’s a perfectionist whose motto is: “if you don’t do it right to begin with, you’ll have to do it again, no matter what the bloody cost and schedule says.” He caused no end of arguments, particularly when the “young astronomers” involved adopted the same motto. The perfectionism was finally controlled, on the surface anyway, by a remarkable project manager, but Jim and the young astronomers kept doing it right on their own time and without permission. The Sloan’s whole value today is that it’s nearly perfect, and this precision has enabled much of its most important contributions. Jim’s now nominally retired and in any case, has turned the survey over to the young astronomers who have, in their turn, turned it over to the whole astronomical community and to the public.

Q: One thing that might surprise readers is how “political” scientists sometimes have to be in working with their colleagues, other institutions, and even asking for funding. Why is this, and has it always been this way?
A: It’s been that way ever since science stopped being a gentleman’s hobby—Jim’s phrase, “gentleman astronomers in their coats and ties”—and began getting funding from foundations and the government. The amount of funding is limited and everyone has to complete for the same small, fixed pot. It’s hair-raising. The astronomical community solves this brilliantly: they find out what everybody else is doing, then they do something different and complementary, and finally they get together and tell the funders what the community’s priorities are. The result is that astronomy keeps getting funded. Meanwhile, individual astronomers are free to be competitive and dog-eat-dog, just as their human nature requires.

Q: What do you hope readers take away from this book?
A: The joy and entertainment of watching these impressively intelligent and persistent guys fumble around until they’ve done something remarkable.

Venus and Mercury Blasted by Recent Solar Storms

A plot of the STEREO data from August 14, 2010, showing the location of the planets and the direction of a CME from the Sun.

Update: Well, it turns out that while it looks like Venus and Mercury are getting pummeled by Coronal Mass Ejections, the geometry might not work out, at least not for every day that is included in the video above. UT reader Steven Janowiecki brought it to my attention that just because Mercury and Venus look close to the Sun doesn’t mean they’re actually in the line of fire, as they could be well behind or in front of the solar storm. I checked with STEREO project scientist Dr. Joseph Gurman, who took a look at the data. He put together a plot for August 14, (see below) and said, “It shows that Mercury and Venus are well to the East (left) of the Sun-earth line. The large CME on the 14th originated from an active region near the west limb of the Sun, and since most CME’s are about 60 degrees of heliolongitude in width on average, it’s unlikely that that event actually passed by Mercury or Venus.” There was one large event, however, on August 7, that appeared likely to be headed in the direction of Mercury and Venus.

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So, as it happens sometimes in astronomy, things are not always as they appear, and this exemplifies the challenges of estimating distance in astronomy.

The STEREO website has a very nifty tool where you can see the location of the spacecraft on any date, as well as where the planets are in their orbits. And there is another tool where you can see and download images from a particular day and time and even put together movies of a specific time period showing STEREO data.

Here’s the rest of the article as it ran originally:

Take a look at these Coronal Mass Ejections (CME) from the first part of August 2010, as seen by the two STEREO spacecraft. Here on Earth, we’ve had some aurorae, a result of the recent solar activity. But this STEREO imagery shows Venus and Mercury were blasted by these CMEs.

STEREO consists of two spacecraft – one ahead of Earth in its orbit, the other trailing behind. With this new pair of viewpoints, scientists are able to see the structure and evolution of solar storms as they blast from the Sun and move out through space.

These movies were taken by SECCHI, a suite of remote sensing instruments on both spacecraft consisting of two white light coronagraphs that make up the Sun Centered Imaging Package (SCIP), as well as a Heliospheric Imager (HI).

SECCHI can follow three-dimensional Coronal Mass Ejections (CMEs) from the Sun’s surface, through the corona and interplanetary medium, to impact at Earth. With these instruments, scientists are getting breakthroughs in understanding the origin and consequences of CMEs, in determining their three-dimensional structure, and more, and perhaps be able to predict space weather. Combining STEREO with the new Solar Dynamics Observatory, we’ll be learning more and more about the Sun in the next few years.

As an example of SDO’s capabilities, here’s an SDO image from earlier today showing the Sun’s limb.

View of the Sun from August 18, 2010 from the Solar Dynamics Observatory. Credit: NASA/SDO

Credit: NASA STEREO/NRL

Amazing New Close-up Images of Enceladus

Caption: Looking down at a plume on Enceladus. Credit: NASA/Space Science Science Institute.

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Oh, wow! This is one of the best images yet from the Cassini spacecraft of the “tiger stripes” in the south polar region of Saturn’s moon Enceladus. Over the weekend, Cassini flew by Enceladus, and has sent back some incredible new images, such as the one above. The tiger stripes are actually giant fissures that spew jets of water vapor and organic particles hundreds of kilometers, or miles, out into space, and here, Cassini is staring right down into one of the fissures. See more great images of Enceladus below, plus images of the moons Dione and Tethys.


Close-up of the cracked, crevassed surface of Enceladus. Credit: NASA/Space Science Institute.

While the winter is darkening the moon’s southern hemisphere, Cassini has its own version of “night vision goggles” — the composite infrared spectrometer instrument – to track heat even when visible light is low. It will take time for scientists to assemble the data into temperature maps of the fissures.

Enceladus against Saturn's limb. Credit: NASA/Space Science Institute.
More plumes on Enceladus. Credit: NASA/Space Science Institute.
Close-up of Tethys. Credit: NASA/Space Science Institute

Dione from 115,370 kilometers away. Credit: NASA/Space Science Institute

See more amazing images from Cassini’s latest at the CICLOPS website.

Emily Lakdawalla at the Planetary Blog also has created some very cool movies from the flyby images.


Hat tip to Stu Atkinson

AEHF-1 Rides Atlas V To Orbit

A United Launch Alliance Atlas V carries the AEHF-1 satellite to orbit.

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The U.S. Air Force successfully launched the first Advanced Extremely High Frequency satellite (AEHF-1) on top of a United Launch Alliance (ULA) Atlas V rocket Saturday, Aug. 14 at 7:07 a.m. EDT. The Atlas V lifted off from Cape Canaveral Air Force Station’s Space Launch Complex 41 (SLC 41) riding a pillar of flame across the morning sky. The window for the launch was two hours long, however it wasn’t needed, the launch occurred on the first attempt. 

“As we expected it was a totally successful launch.” said U.S. Air Force Captain Glorimar Rodriguez.

The AEHF constellation of satellites will replace the aging Milstar satellites. The more-modern AEHF is designed to ensure rapid communications for military leaders. This new, jam-proof system will be the link between the president and the armed forces in the event of a nuclear attack. Lockheed Martin is the prime contractor to construct both the AEHF fleet of satellites as well as the mission control center where the satellites will be operated.

AEHF launch. Credit: Alan Walters (awaltersphoto.com) for Universe Today

There are a number of U.S. allies that are involved with the AEHF program and can use these satellites once the system is activated. Some of these allies include the Netherlands, Canada and the United Kingdom.

When the system is complete it will be comprised of three functioning satellites and a spare satellite. These satellites will be inter-connected and are capable of communicating with one another. They will provide the military with vital communications-related data including, but not limited to, maps, video and targeting data. When operational, the AEHF constellation will be operated by the 4th Space Operations Squadron, who are stationed at Schriever Air Force Base, CO.

Pre-launch. Cape Canaveral Air Force Station’s Space Launch Complex 41. Credit: Alan Walters (awaltersphoto.com) for Universe Today

Astrophotography Spotlight – Centaurus A

“I’m on rhe outside… I’m lookin’ in.” And just who are we looking in at this time? None other than the familiar face of Centaurus A.. The stunning, turbulent dust lane is cloaked in the ethereal mist of living galaxy stuff – the result of a gravitationally hungry elliptical galaxy drawing a smaller companion spiral galaxy towards its demise. Like a spider waiting in the center of a web, the black hole at the heart of NGC 5128 takes no prisoners. Its complexity screams out to us in radio, X-ray, and gamma-ray energy. “I can see through you… See the real you.”

It waits in space some 10 to 11 million light years away. It’s the nearest active galaxy to Earth and contains a core black hole estimated to be a billion times the mass of our Sun. The result of Centaurus A’s merger event is so incredibly powerful that it may have even shifted the axis of the massive black hole from its expected orientation – an area not much larger than our own solar system. “The variability of the nucleus may represent the accretion of individual stellar or cloud remnants onto the black hole triggering renewed jet activity and fueling the radio source.” says F.P. Israel. “Details of these processes are not clear yet, but careful and frequent monitoring of Centaurus A at radio, X-ray and -ray wavelengths may provide important information. For instance, how does the nucleus drive the nuclear jets, and how are the relativistic nuclear jets transformed into the nonrelativistic inner jets? The circumnuclear disk does not seem capable of controlling the collimation of the nuclear jets, but its orientation exactly perpendicular to these jets, suggests that it is somehow connected with the collimating agent.”

Could it be the unique properties of Centaurus A originate from its cannibalizing an equally unique galaxy? If you examine the full size image by Ken Crawford you’ll find many background galaxies hidden amongst the stars. What we may very well be viewing is the early results of an giant elliptical merging with a much small spiral structure – creating a stunning halo. “When most people think of NGC 5128 (also known as Centaurus A) they see radio jets, central black holes, a very visible accretion disk and more. But these are “icing on the cake” of the underlying giant E galaxy.” says Gretchen Harris (University of Waterloo). “We now know the it has a fairly normal old halo system as seen in its globular clusters, planetary nebulae, and red giant stars. Its proximity makes NGC 5128 an ideal template for understanding the properties of large E galaxies in general.”

While science may consider Centaurus A to be a template, its tortured form makes it an incredible palette to the eye of the camera. Utilizing a RCOS 14.5″ Truss telescope and taking various exposures for nearly two hours, Ken has produced an image which reveals intricate details almost as fine as the 7 light-year resolution photos taken by the Hubble Space telescope.

Here you will see clumps of hot, young blue stars which have newly formed and the pink signature of star forming regions – as well as the release of gas which hasn’t conformed to the spin axis of the central black hole. Maybe two black holes duking it out? “This black hole is doing its own thing. Aside from receiving fresh fuel from a devoured galaxy, it may be oblivious to the rest of the galaxy and the collision,” said Ethan Schreier of the Space Telescope Science Institute. “”We have found a complicated situation of a disk within a disk within a disk, all pointing in different directions. It is not clear if the black hole was always present in the host galaxy or belonged to the spiral galaxy that fell into the core, or if it is the product of the merger of a pair of smaller black holes that lived in the two once-separate galaxies.”

Although the galactic merger may have began around 200 to 700 million years ago, the incredible arcs of multi-million degree gas remain in a 25,000 light-year diameter wobbling ring producing high energy jets. Given its size and location this ring might very well be a galaxy-sized shockwave – the million mile per hour outward ripples of an intense explosion which may have occurred some 10 million years ago. “We believe that most of these stars formed from the interaction of the jet with local concentrations of dust and gas.” says John Graham. “The brightest blue stars are presumably the youngest stars and tend to lie close to the X-ray jet. We suggest that the raw material for star formation is found in dust patches of small angular size in the area and that star formation is triggered by shocks initiated by the jet.”

Now I want you to take a closer look. What you are going to discover (highlighted by the small arrow) is a thin, blue smear of newly formed stars. It’s something you’d probably never notice unless it was pointed out to you.

What you are seeing is a thousand light year long band of scar tissue. A dead giveaway of a recent galactic absorption. Astronomers had previously noticed the arc now identified as a galactic merger remnant, but without recognizing its origin. “This adds a nice example in the local universe to the growing evidence that galaxy halos are built up from the accretion of dwarf satellite galaxies,” said Eric Peng, a graduate student in astronomy at Johns Hopkins University. “These halos are interesting partly because they’re hard to study, but also because time scales for things to happen in halos are very long, which means they may preserve conditions that reveal how a galaxy formed and evolved.”

But for now? “I’m on the outside… And I’m lookin’ in. I can see through you… See your true colors.”

Many thanks to Ken Crawford for his exquisite work which led to a wonderfully pleasant day of researching the ins and outs of a most remarkable galaxy!

Astronomy Without A Telescope – Alchemy By Supernova

(Caption) Supernova remnant G1.9+0.3 (Combined image from Chandra Xray data and radio data from NRAO's Very Large Array). Credit: http://chandra.harvard.edu

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The production of elements in supernova explosions is something we take for granted these days. But exactly where and when this nucleosynthesis takes place is still unclear – and attempts to computer model core collapse scenarios still pushes current computing power to its limits.

Stellar fusion in main sequence stars can build some elements up to, and including, iron. Further production of heavier elements can also take place by certain seed elements capturing neutrons to form isotopes. Those captured neutrons may then undergo beta decay leaving behind one or more protons which essentially means you have a new element with a higher atomic number (where atomic number is the number of protons in a nucleus).

This ‘slow’ process or s-process of building heavier elements from, say, iron (26 protons) takes place most commonly in red giants (making elements like copper with 29 protons and even thallium with 81 protons).

But there’s also the rapid or r-process, which takes place in a matter of seconds in core collapse supernovae (being supernova types 1b, 1c and 2). Rather than the steady, step-wise building over thousands of years seen in the s-process – seed elements in a supernova explosion have multiple neutrons jammed in to them, while at the same time being exposed to disintegrating gamma rays. This combination of forces can build a wide range of light and heavy elements, notably very heavy elements from lead (82 protons) up to plutonium (94 protons), which cannot be produced by the s-process.

How stuff gets made in our universe. The white elements (above plutonium) can be formed in a laboratory, but it is unclear whether they form naturally - and, in any case, they decay quickly after they are formed. Credit: North Arizona University

Prior to a supernova explosion, the fusion reactions in a massive star progressively run through first hydrogen, then helium, carbon, neon, oxygen and finally silicon  – from which point an iron core develops which can’t undergo further fusion. As soon as that iron core grows to 1.4 solar masses (the Chandrasekhar limit) it collapses inwards at nearly a quarter of the speed of light as the iron nuclei themselves collapse.

The rest of the star collapses inwards to fill the space created but the inner core ‘bounces’ back outwards as the heat produced by the initial collapse makes it ‘boil’. This creates a shockwave – a bit like a thunderclap multiplied by many orders of magnitude, which is the beginning of the supernova explosion. The shock wave blows out the surrounding layers of the star – although as soon as this material expands outwards it also begins cooling. So, it’s unclear if r-process nucleosynthesis happens at this point.

But the collapsed iron core isn’t finished yet. The energy generated as the core compressed inwards disintegrates many iron nuclei into helium nuclei and neutrons. Furthermore, electrons begin to combine with protons to form neutrons so that the star’s core, after that initial bounce, settles into a new ground state of compressed neutrons – essentially a proto-neutron star. It is able to ‘settle’ due to the release of a huge burst of neutrinos which carries heat away from the core.

It’s this neutrino wind burst that drives the rest of the explosion. It catches up with, and slams into, the already blown-out ejecta of the progenitor star’s outer layers, reheating this material and adding momentum to it. Researchers (below) have proposed that it is this neutrino wind impact event (the ‘reverse shock’) that is the location of the r-process.

It’s thought that the r-process is probably over within a couple of seconds, but it could still take an hour or more before the supersonic explosion front bursts through the surface of the star, delivering some fresh contributions to the periodic table.

Further reading: Arcones A. and Janka H. Nucleosynthesis-relevant conditions in neutrino-driven supernova outflows. II. The reverse shock in two-dimensional simulations.

And, for historical context, the seminal paper on the subject (also known as the B2FH paper) E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle. (1957). Synthesis of the Elements in Stars. Rev Mod Phy 29 (4): 547. (Before this nearly everyone thought all the elements formed in the Big Bang – well, everyone except Fred Hoyle anyway).

Clockwork Planets

Bottoms up! Mercury, Moon, Saturn, Venus, Mars...

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While the Perseid meteor shower has been putting on quite a show, there’s an awesome “no telescope needed” eye-catching apparition that only requires a clear western skyline. If you haven’t been watching the planets – Mercury, Saturn, Venus and Mars – line up like clockwork, then don’t despair. You have a few more days yet!

While the uniformed all-too-often see “signs of bad portent” in a planetary alignment, the rest of us know this is a perfectly normal function of our solar system called a conjunction. This is a simple positional alignment as seen (usually from Earth’s viewpoint) from any given vantage point. The world isn’t going to end, the oceans aren’t going to rise… and Mars is darn-sure not going to be the size of the Moon. All alignments of at least two celestial bodies are merely coincidental and we even have a grand name for what’s happening – an appulse.

When planets are involved, their near appearance usually happens in the same right ascension. They really aren’t any closer to each other than what their orbital path dictates – it just appears that way. In the same respect, there is also conjunction in ecliptical longitude. But, if the planet nearer the Earth should happen to pass in front of another planet during a conjunction it’s called a syzygy!

One thing is for sure… You don’t have to be a syzy-genius to simply enjoy the show and the predictable movements of our solar system. Just find an open western skyline and watch as twilight deepens. Tonight the Moon will be directly south of Venus and over the next couple of days the planetary alignment will gradually separate as brilliant Venus seems to hold its position, while Mars, Saturn and Mercury drift north. Enjoy the show! Because just like the yearly Mars/Moon Myth?

It happens like clockwork…

Many, many thanks to the incredible Shevill Mathers for providing us with this breathtaking photo. (Do you know just how hard it is to get a shot like that without over or under exposing? I dare you to try it…) Every fox has a silver lining!