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Viewing: Blog Posts Tagged with: astronomy, Most Recent at Top [Help]
Results 1 - 25 of 56
1. Space travel to improve health on earth

World Space Week has been celebrated for the last 17 years, with events taking place all over the world, making it one of the biggest public events in the world. Highlighting the research conducted and achievements reached, milestones are celebrated in this week. The focus isn’t solely on finding the ‘Final Frontier’ but also on how the research conducted can be used to help humans living on Earth.

The post Space travel to improve health on earth appeared first on OUPblog.

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2. Shakespeare and the natural world [infographic]

It is probable that Shakespeare observed, or at least heard about, many natural phenomena that occurred during his time, which may have influenced the many references to nature and science that he makes in his work. Although he was very young at the time, he may have witnessed the blazing Stella Nova in 1572.

The post Shakespeare and the natural world [infographic] appeared first on OUPblog.

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3. The world’s most (in)famous exoplanet vanishes

In 2012, a team of astrophysicists led by Xavier Dumusque caused a sensation when they announced the discovery of Alpha Centauri Bb: an Earth-sized planet in the Alpha Centauri star system, the star system closest to the Sun. If verified, Alpha Centauri Bb would be the closest known exoplanet to our own Solar System, and possibly also the lowest mass planet ever discovered around a star similar to the Sun.

The post The world’s most (in)famous exoplanet vanishes appeared first on OUPblog.

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4. An efficient way to find monsters with two faces

Quasars are distant galactic nuclei generating spectacular amounts of energy by matter accretion onto their central supermassive black holes. The precise geometry and origin of this huge activity are still largely unknown, and direct spatial resolution of the emitting regions from such distant monsters is not currently possible.

The post An efficient way to find monsters with two faces appeared first on OUPblog.

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5. Adding a new dimension to the early chemistry of the solar system

What was our solar system composed of right after its formation? Using sophisticated computer simulations, researchers from France and Australia have obtained new insights into the chemical composition of the dust grains that formed in the early solar system which went on to form the building blocks of the terrestrial planets.

The post Adding a new dimension to the early chemistry of the solar system appeared first on OUPblog.

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6. How much do you know about Hypatia? [quiz]

An astronomer, mathematician, philosopher, and active public figure, Hypatia played a leading role in Alexandrian civic affairs. Her public lectures were popular, and her technical contributions to geometry, astronomy, number theory, and philosophy made Hypatia a highly regarded teacher and scholar.

The post How much do you know about Hypatia? [quiz] appeared first on OUPblog.

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7. Time as a representation in physics

A previous blog post, Patterns in Physics, discussed alternative “representations” in physics as akin to languages; an underlying quantum reality described in either a position or a momentum representation. Both are equally capable of a complete description, the underlying reality itself residing in a complex space with the very concepts of position/momentum or wave/particle only relevant in a “classical limit”. The history of physics has progressively separated such incidentals of our description from what is essential to the physics itself. We will consider this for time itself here.

Thus, consider the simple instance of the motion of a ball from being struck by a bat (A) to being caught later at a catcher’s hand (B). The specific values given for the locations of A and B or the associated time instants are immediately seen as dependent on each person in the stadium being free to choose the origin of his or her coordinate system. Even the direction of motion, whether from left to right or vice versa, is of no significance to the physics, merely dependent on which side of the stadium one is sitting.

All spectators sitting in the stands and using their own “frame of reference” will, however, agree on the distance of separation in space and time of A and B. But, after Einstein, we have come to recognize that these are themselves frame dependent. Already in Galilean and Newtonian relativity for mechanical motion, it was recognized that all frames travelling with uniform velocity, called “inertial frames”, are equivalent for physics so that besides the seated spectators, a rider in a blimp moving overhead with uniform velocity in a straight line, say along the horizontal direction of the ball, is an equally valid observer of the physics.

Einstein’s Special Theory of Relativity, in extending the equivalence of all inertial frames also to electromagnetic phenomena, recognized that the spatial separation between A and B or, even more surprisingly to classical intuition, the time interval between them are different in different inertial frames. All will agree on the basics of the motion, that ball and bat were coincident at A and ball and catcher’s hand at B. But one seated in the stands and one on the blimp will differ on the time of travel or the distance travelled.

Even on something simpler, and already in Galilean relativity, observers will differ on the shape of the trajectory of the ball between A and B, all seeing parabolas but of varying “tightness”. In particular, for an observer on the blimp travelling with the same horizontal velocity as that of the ball as seen by the seated, the parabola degenerates into a straight up and down motion, the ball moving purely vertically as the stadium itself and bat and catcher slide by underneath so that one or the other is coincident with the ball when at ground level.

hourglass
Hourglass, photo by Erik Fitzpatrick, CC-BY-2.0 via Flickr

There is no “trajectory of the ball’s motion” without specifying as seen by which observer/inertial frame. There is a motion, but to say that the ball simultaneously executes many parabolic trajectories would be considered as foolishly profligate when that is simply because there are many observers. Every observer does see a trajectory, but asking for “the real trajectory”, “What did the ball really do?”, is seen as an invalid, or incomplete, question without asking “as seen by whom”. Yet what seems so obvious here is the mistake behind posing as quantum mysteries and then proposing as solutions whole worlds and multiple universes(!). What is lost sight of is the distinction between the essential physics of the underlying world and our description of it.

The same simple problem illustrates another feature, that physics works equally well in a local time-dependent or a global, time-independent description. This is already true in classical physics in what is called the Lagrangian formulation. Focusing on the essential aspects of the motion, namely the end points A and B, a single quantity called the action in which time is integrated over (later, in quantum field theory, a Lagrangian density with both space and time integrated over) is considered over all possible paths between A and B. Among all these, the classical motion is the one for which the action takes an extreme (technically, stationary) value. This stationary principle, a global statement over all space and time and paths, turns out to be exactly equivalent to the local Newtonian description from one instant to another at all times in between A and B.

There are many sophisticated aspects and advantages of the Lagrangian picture, including its natural accommodation of   basic conservation laws of energy, momentum and angular momentum. But, for our purpose here, it is enough to note that such stationary formulations are possible elsewhere and throughout physics. Quantum scattering phenomena, where it seems natural to think in terms of elapsed time during the collisional process, can be described instead in a “stationary state” picture (fixed energy and standing waves), with phase shifts (of the wave function) that depend on energy, all experimental observables such as scattering cross-sections expressed in terms of them.

“The concept of time has vexed humans for centuries, whether layman, physicist or philosopher”

No explicit invocation of time is necessary although if desired so-called time delays can be calculated as derivatives of the phase shifts with respect to energy. This is because energy and time are quantum-mechanical conjugates, their product having dimensions of action, and Planck’s quantum constant with these same dimensions exists as a fundamental constant of our Universe. Indeed, had physicists encountered quantum physics first, time and energy need never have been invoked as distinct entities, one regarded as just Planck’s constant times the derivative (“gradient” in physics and mathematics parlance) of the other. Equally, position and momentum would have been regarded as Planck’s constant times the gradient in the other.

The concept of time has vexed humans for centuries, whether layman, physicist or philosopher. But, making a distinction between representations and an underlying essence suggests that space and time are not necessary for physics. Together with all the other concepts and words we perforce have to use, including particle, wave, and position, they are all from a classical limit with which we try to describe and understand what is actually a quantum world. As long as that is kept clearly in mind, many mysteries and paradoxes are dispelled, seen as artifacts of our pushing our models and language too far and “identifying” them with the underlying reality that is in principle out of reach.

The post Time as a representation in physics appeared first on OUPblog.

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8. Star Stuff: Carl Sagan and the Mysteries of the Cosmos - a review

Sisson, Stephanie Roth. 2014. Star Stuff: Carl Sagan and the mysteries of the cosmos. New York: Roaring Brook.


In simple text augmented by word bubbles, thought bubbles, and sketches, Stephanie Roth Sisson gives us the highlights of Carl Sagan's lifebut more importantly, she offers a sense of his wondrous enthusiasm for the cosmos,

It gave Carl goose bumps to think about what he had learned about the stars, planets, and the beginnings of life.  He wanted everyone to understand so that they could feel like a part of the stars as he did.
So he went on television.


This is the first book that Stephanie Roth Sisson has both written and illustrated.  The fact that she is enthralled with her subject is apparent in the artwork. Painted cartoon images (often in panels with word bubbles), depict a happy Sagan, wide-eyed and curious.  While some pages are like panel comics, others are full-bleed, double spreads depicting the vastness of the darkened skies, dotted by planets or stars.  One foldout opens vertically, reminding us of our infinitesimal existence in the cosmos.  We are so small, yet we are reminded,

The Earth and every living thing are made of star stuff.
Star Stuff is a 2015 NCTE Orbis Pictus Award Honor book for "outstanding nonfiction for children."

Substantial back matter includes Author's Note, Notes, Bibliography and Sources, Special Thanks, and Source Notes.

Preview the first eight pages of Star Stuff on the publisher's website.

Note: 
Carl Sagan graduated from Rahway High School in Rahway, NJ.  As far as I can tell, he's not mentioned anywhere on the school's website. Pity.


It's STEM Friday! (STEM is Science, Technology, Engineering, and Mathematics)
See all of today's STEM-related posts at the STEM Friday blog.

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9. I Want His Job

Headline news can be depressing. Which is why it makes me happy to find news stories like this one: This Teenager Discovered a New Planet on his Third Day of Work. Seriously. At 15, this kid shows up for day three of his “work experience” project, they’ve assigned him the task of wading through all […]

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10. How are beasts of the stellar zoo born?

In the same way as a jungle harbours several species of birds and mammals, the stellar (or almost stellar) zoo also offers a variety of objects with different sizes, masses, temperatures, ages, and other physical properties. On the one hand, there are huge massive stars that easily overshadow one as the Sun. On the other, there are less graceful, but still very interesting inhabitants: small low-mass stars or objects that come out of the stellar classification. These last objects are called "brown dwarfs".

The post How are beasts of the stellar zoo born? appeared first on OUPblog.

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11. The science of rare planetary alignments

The alignment of both the Sun and the Earth with another planet in the Solar System is a rare event, which we are seldom able to observe in a lifetime.

The post The science of rare planetary alignments appeared first on OUPblog.

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12. NASA discovers water on Mars again: take it with a pinch of salt

The discovery of water on Mars has been claimed so often that I’d forgive anyone for being skeptical about the latest announcement. Frozen water, ice, has been proven on Mars in many places, there are lots of ancient canyons hundreds of kilometres long that must have been carved by rivers, and much smaller gullies that are evidently much younger.

The post NASA discovers water on Mars again: take it with a pinch of salt appeared first on OUPblog.

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13. Thinking of Kepler on the beach

Johannes Kepler, the astronomer who famously discovered that planets move in ellipses, presents an exceptional case we can reconstruct. Kepler got his assistant to paint an image of himself for a friend. This was just before Kepler stored up all his belongings to move his family back from Austria to Germany. His aged mother had been accused of witchcraft.

The post Thinking of Kepler on the beach appeared first on OUPblog.

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14. Place of the Year nominee spotlight: Dwarf planet Pluto

This July, a NASA space probe completed our set of images of the planets, at least as I knew them growing up. New Horizons, a probe that launched back in 2006, arrived at Pluto and its moons, and over a very brief encounter, started to send back thousands of images of this hitherto barely known place.

The post Place of the Year nominee spotlight: Dwarf planet Pluto appeared first on OUPblog.

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15. How High the Biosphere?

Like stratosphere, troposphere, and mesosphere, atmospheric regions with which it shares part of its name, the biosphere is a shell-shaped zone enveloping our planet. But where the others are made of nitrogen, oxygen, water vapor, and trace gases, the biosphere is made of life. It extends in two directions — up and down — farther [...]

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16. A record-breaking lunar impact

By Jose M. Madiedo


On 11 September 2013, an unusually long and bright impact flash was observed on the Moon. Its peak luminosity was equivalent to a stellar magnitude of around 2.9.

What happened? A meteorite with a mass of around 400 kg hit the lunar surface at a speed of over 61,000 kilometres per hour.

Rocks often collide with the lunar surface at high speed (tens of thousands of kilometres per hour) and are instantaneously vaporised at the impact site. This gives rise to a thermal glow that can be detected by telescopes from Earth as short duration flashes. These flashes, in general, last just a fraction of a second.

The extraordinary flash in September was recorded from Spain by two telescopes operating in the framework of the Moon Impacts Detection and Analysis System (MIDAS). These devices were aimed to the same area in the night side of the Moon. With a duration of over eight seconds, this is the brightest and longest confirmed impact flash ever recorded on the Moon.

Click here to view the embedded video.

Our calculations show that the impact, which took place at 20:07 GMT, created a new crater with a diameter of around 40 meters in Mare Nubium. This rock had a size raging between 0.6 and 1.4 metres. The impact energy was equivalent to over 15 tons of TNT under the assumption of a luminous efficiency of 0.002 (the fraction of kinetic energy converted into visible radiation as a consequence of the hypervelocity impact).

The detection of impact flashes is one of the techniques suitable to analyze the flux of incoming bodies to the Earth. One of the characteristics of the lunar impacts monitoring technique is that it is not possible to unambiguously associate an impact flash with a given meteoroid stream. Nevertheless, our analysis shows that the most likely scenario is that the impactor had a sporadic origin (i.e., was not associated to any known meteoroid stream). From the analysis of this event we have learnt that that one metre-sized objects may strike our planet about ten times as often as previously thought.

Dr. Jose Maria Madiedo is a professor at Universidad de Huelva. He is the author of “A large lunar impact blast on 2013 September 11” in the most recent issue of the Monthly Notices of the Royal Astronomical Society.

Monthly Notices of the Royal Astronomical Society is one of the world’s leading primary research journals in astronomy and astrophysics, as well as one of the longest established. It publishes the results of original research in astronomy and astrophysics, both observational and theoretical.

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17. I should get an award or something

Not sure why scientists are so ga-ga over figuring out what black holes really are. I’ve already done that. And I know how they are formed. Revisions = black holes Revisions are formed when first drafts become second drafts, third drafts, fourth drafts, etc. An endless loop of deletions and additions that suck the writer…

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18. Total Eclipse of the Moon

redmoonTax day approaches – everyone's favorite day of the year. Tonight I plan to stay up past midnight and watch the day arrive. Not because I waited until the last minute to do my taxes (although there's that) but because tonight there will be a total lunar eclipse.

Most of North America will be able to see the eclipse and since the moon is close to full it should be pretty dramatic. Because of the timing of the eclipse, sunsets and sunrises in other parts of the world will make the moon look blood red. Kinda cool! If you have cloudy skies or too many city lights to see it, The Griffith Observatory in Los Angeles will broadcast the eclipse live starting at 9:45 p.m. PST.

This is also the last week of the blog tour for WISH YOU WEREN'T. Here are the planned stops.  

MONDAY
The Book Cellar: Erica posts an interview about my reading and writing habits.  
Books and Needlepoint: Kristi will post her review of Wish You Weren't.  

WEDNESDAY 
Book Loving Mom: Amy will post her review of Wish You Weren't.

I want to thank all of the bloggers who hosted me during this tour. Book bloggers are seriously the coolest people. They don't make money from this. They do it because they love books and I'm totally honored to have been part of so many awesome blogs.

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19. How I Killed Pluto: And Why It Had It Coming

How I Killed Pluto and Why It Had It Coming Mike Brown

Ever since he was a kid, Brown wanted to discover planets. But, when he did discover some, instead of being excited he discovered a planet, he realized that, really, Pluto shouldn’t count as a planet, because that made what he was finding make a lot more sense.

Brown is a hilarious and fascinating as he tells us about the development of thought about the solar system, how modern astronomy works (it’s a lot of coding!), why Pluto isn’t a planet, and his own life. Plus, oh the shennanigans and in-fighting (astronomer politics! who knew?!)

Not a lot of scientists can write like this- heck, not a lot of writers can write like this. It’s a wonderful and fascinating book that really digs into the story-behind-the-story of when Pluto stopped being a planet.

Book Provided by... my local library

Links to Amazon are an affiliate link. You can help support Biblio File by purchasing any item (not just the one linked to!) through these links. Read my full disclosure statement.

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20. The End of Night (staff pick)

Remarkably, estimates are that eight out of every ten children born in America today will never know "what it means." That is, 80 percent will never know a night dark enough that they can see the Milky Way. Remarkable and depressing. The End of Night follows author Paul Bogard as he travels the world to [...]

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21. Space Camp: The Final Frontier

Writing Life Banner

by

E.C. Myers

20140714_213020A couple of weeks ago, I was thrilled to participate in one of the most exciting and memorable things I’ve ever done: the Launch Pad Astronomy Workshop. Dubbed a “space camp for writers,” it brings together established writers, editors, and creators for an intensive, week-long crash course in astronomy: basically a semester’s worth of Astronomy 101 classes in  seven days. It was breathtaking (literally—it takes place in Laramie, Wyoming, about 7,100 feet above sea level), mind-blowing, and, most of all, inspiring.

It was inspiring not only because of all the story ideas it generated and the opportunity to learn more about our incredible, mysterious universe, but because there’s nothing like meeting and spending time with other writers and creative professionals. The 2014 class included authors, reviewers, editors, and television and film writers: Amy Sterling CasilGeetanjali DigheDoug Farren,Susan ForestMarc HalseyGabrielle HarbowyMeg HowreyAnn LeckieWilliam LedbetterAndrew LiptakMalinda LoSarah McCarryJames L. Sutter, Anne TooleTodd Vandemark, and Lisa Yee. Our intrepid instructors were Mike Brotherton, Christian Ready, and Andria Schwortz, whose enthusiasm for their field was apparent and contagious.

We were in class almost every day from 10 a.m. until well after 5 p.m., with some lab sessions and outings thrown in. So what sort of things did we learn? Just as an example, our Monday lectures included the Scales of the Universe, Units, the Solar System, Seasons and Lunar Phases, and Misconceptions about Astronomy. By Friday and Saturday we were discussing galaxies, quasars, and cosmology (including dark matter and dark energy). That’s quite the learning curve! Most of us felt like our heads were full by the end, yet we were always eager to hear more.

Yup. That is totally an exoplanet.

Yup. That is totally an exoplanet.

I know I must have learned some of this stuff in elementary school (and forgotten most of it), but there have also been so many breakthroughs in astronomy since I was a kid (sorry, Pluto!), I was learning much of this for the first time — and I also had a new appreciation for the topic. Every class was a revelation. What made it even better was having the opportunity to see the science we were learning at work: analyzing the emission spectrum of different elements in the lab, searching for exoplanets at planethunters.org (warning — that site is addictive!), learning how those famous images of space are put together for the public, and visiting the University of Wyoming Infrared Observatory to photograph stars with a giant telescope. It was there, at the top of Jelm Mt., that I experienced the highlight of my week: viewing the Milky Way with the naked eye in a clear night sky. (It also looks very impressive in expensive night vision binoculars.) Returning home and looking up at night was depressing; the city lights blot out all but the brightest stars, and I can imagine that some people go their whole lives without seeing a sight like that.

Copyright Todd Vandemark

© 2014 Todd Vandemark

People always ask writers, “Where do you get your ideas?” Look up. Look around you. Ideas are all around us! As a science fiction author who doesn’t have a background in science, all too often I get distracted by fun concepts like time travel and parallel universes and faster-than-light space travel. It’s so easy to forget just how fascinating and exciting actual science is and skimp on it in stories. Why make everything up when we have a whole galaxy to play with, and an even bigger universe full of weird and mind-boggling things?

I’ve always enjoyed doing research for stories, but from now on I’m going to pay more attention to what’s happening in astronomy and physics and the world and universe we live in — and hopefully the things I learn will inspire new stories, instead of the other way around. (Added bonus of the workshop: Now I actually understand those astronomy articles in Scientific American!)

We also stopped by the Geological Museum at the University of Wyoming. I love dinosaurs. Meet Dracorex hogwartsia, "Dragon King of Hogwarts"!

We also stopped by the Geological Museum at the University of Wyoming. I love dinosaurs. Meet Dracorex hogwartsia, “Dragon King of Hogwarts”!

I want to continue learning about astronomy, and work real science into more of my fiction. It’s important to keep “refilling your creative well,” and Launch Pad was a great way to do that. If you’re a science fiction writer, I encourage you to apply to next year’s workshop, and I also encourage you to donate to keep the program going. It’s a wonderful resource that is helping to get more people interested in science, and helping we writers to make our stories as scientifically plausible and accurate as we can.

For other perspectives on this year’s Launch Pad experience, read accounts from my awesome classmates and instructor:

Gabrielle Harbowy
Andrew Liptak
Sarah McCarry
Christian Ready
Jenn Reese

How about you? Would you go to Launch Pad? How do you refill your creative well?

LaunchPad

E.C. Myers was assembled in the U.S. from Korean and German parts and raised by a single mother and a public library in Yonkers, New York. He is the author of the Andre Norton Award–winning young adult novel FAIR COIN and its sequel, QUANTUM COIN; his next YA novel, THE SILENCE OF SIX, will be published by Adaptive in November 2014. You can find traces of him all over the internet, but especially at his blogTwitter, Facebook, and Tumblr.

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22. Are we alone in the Universe?

World Space Week has prompted myself and colleagues at the Open University to discuss the question: ‘Is there life beyond Earth?’

The bottom line is that we are now certain that there are many places in our Solar System and around other stars where simple microbial life could exist, of kinds that we know from various settings, both mundane and exotic, on Earth. What we don’t know is whether any life does exist in any of those places. Until we find another example, life on Earth could be just an extremely rare fluke. It could be the only life in the whole Universe. That would be a very sobering thought.

At the other extreme, it could be that life pops up pretty much everywhere that it can, so there should be microbes everywhere. If that is the case, then surely evolutionary pressures would often lead towards multicellular life and then to intelligent life. But if that is correct – then where is everybody? Why can’t we recognise the signs of great works of astroengineering by more ancient and advanced aliens? Why can’t we pick up their signals?

The chemicals from which life can be made are available all over the place. Comets, for example, contain a wide variety of organic molecules. They aren’t likely places to find life, but collisions of comets onto planets and their moons should certainly have seeded all the habitable places with the materials from which life could start.

So where might we find life in our Solar System? Most people think of Mars, and it is certainly well worth looking there. The trouble is that lumps of rock knocked off Mars by asteroid impacts have been found on Earth. It won’t have been one-way traffic. Asteroid impacts on Earth must have showered some bits of Earth-rock onto Mars. Microbes inside a rock could survive a journey in space, and so if we do find life on Mars it will be important to establish whether or not it is related to Earth-life. Only if we find evidence of an independent genesis of life on another body in our Solar System will we be able to conclude that the probability of life starting, given the right conditions, is high.

A colour image of comet 67/P from Rosetta’s OSIRIS camera. Part of the ‘body’ of the comet is in the foreground. The ‘head’ is in the background, and the landing site where the Philae lander will arrive on 12 November 2014 is out of view on the far side of the ‘head’. (Patrik Tschudin, CC-BY-2.0 via Flickr)

For my money, Mars is not the most likely place to find life anyway. The surface environment is very harsh. The best we might hope for is some slowly-metabolising rock-eating microbes inside the rock. For a more complex ecosystem, we need to look inside oceans. There is almost certainly liquid water below the icy crust of several of the moons of the giant planets – especially Europa (a moon of Jupiter) and Enceladus (a moon of Saturn). These are warm inside because of tidal heating, and the way-sub-zero surface and lack of any atmosphere are irrelevant. Moreover, there is evidence that life on Earth began at ‘hydrothermal vents’ on the ocean floor, where hot, chemically-rich, water seeps or gushes out. Microbes feed on that chemical energy, and more complex organisms graze on the microbes. No sunlight, and no plants are involved. Similar vents seem pretty likely inside these moons – so we have the right chemicals and the right conditions to start life – and to support a complex ecosystem. If there turns out to be no life under Europa’s ice them I think the odds of life being abundant around other stars will lengthen considerably.

We think that Europa’s ice is mostly more than 10 km thick, so establishing whether or not there is life down there wont be easy. Sometimes the surface cracks apart and slush is squeezed out to form ridges, and these may be the best target for a lander, which might find fossils entombed in the slush.

Enceladus is smaller and may not have such a rich ocean, but comes with the big advantage of spraying samples of its ocean into space though cracks near its south pole (similar plumes have been suspected at Europa, but not proven). A properly equipped spaceprobe could fly through Enceladus’s eruption plumes and look for chemical or isotopic traces of life without needing to land.

I’m sure you’ll agree, moons are fascinating!

Headline image credit: Center of the Milky Way Galaxy, from NASA’S Marshall Space Flight Center. CC-BY-ND-2.0 via Flickr.

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23. Patterns in physics

The aim of physics is to understand the world we live in. Given its myriad of objects and phenomena, understanding means to see connections and relations between what may seem unrelated and very different. Thus, a falling apple and the Moon in its orbit around the Earth. In this way, many things “fall into place” in terms of a few basic ideas, principles (laws of physics) and patterns.

As with many an intellectual activity, recognizing patterns and analogies, and metaphorical thinking are essential also in physics. James Clerk Maxwell, one of the greatest physicists, put it thus: “In a pun, two truths lie hid under one expression. In an analogy, one truth is discovered under two expressions.”

Indeed, physics employs many metaphors, from a pendulum’s swing and a coin’s two-sidedness, examples already familiar in everyday language, to some new to itself. Even the familiar ones acquire additional richness through the many physical systems to which they are applied. In this, physics uses the language of mathematics, itself a study of patterns, but with a rigor and logic not present in everyday languages and a universality that stretches across lands and peoples.

Rigor is essential because analogies can also mislead, be false or fruitless. In physics, there is an essential tension between the analogies and patterns we draw, which we must, and subjecting them to rigorous tests. The rigor of mathematics is invaluable but, more importantly, we must look to Nature as the final arbiter of truth. Our conclusions need to fit observation and experiment. Physics is ultimately an experimental subject.

Physics is not just mathematics, leave alone as some would have it, that the natural world itself is nothing but mathematics. Indeed, five centuries of physics are replete with instances of the same mathematics describing a variety of different physical phenomena. Electromagnetic and sound waves share much in common but are not the same thing, indeed are fundamentally different in many respects. Nor are quantum wave solutions of the Schroedinger equation the same even if both involve the same Laplacian operator.

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Advanced Theoretical Physics by Marvin (PA). CC-BY-NC-2.0 via mscolly Flickr.

Along with seeing connections between seemingly different phenomena, physics sees the same thing from different points of view. Already true in classical physics, quantum physics made it even more so. For Newton, or in the later Lagrangian and Hamiltonian formulations that physicists use, positions and velocities (or momenta) of the particles involved are given at some initial instant and the aim of physics is to describe the state at a later instant. But, with quantum physics (the uncertainty principle) forbidding simultaneous specification of position and momentum, the very meaning of the state of a physical system had to change. A choice has to be made to describe the state either in terms of positions or momenta.

Physicists use the word “representation” to describe these alternatives that are like languages in everyday parlance. Just as with languages, where one needs some language (with all equivalent) not only to communicate with others but even in one’s own thinking, so also in physics. One can use the “position representation” or the “momentum representation” (or even some other), each capable of giving a complete description of the physical system. The underlying reality itself, and most physicists believe that there is one, lies in none of these representations, indeed residing in a complex space in the mathematical sense of complex versus real numbers. The state of a system in quantum physics is in such a complex “wave function”, which can be thought of either in position or momentum space.

Either way, the wave function is not directly accessible to us. We have no wave function meters. Since, by definition, anything that is observed by our experimental apparatus and readings on real dials, is real, these outcomes access the underlying reality in what we call the “classical limit”. In particular, the step into real quantities involves a squared modulus of the complex wave functions, many of the phases of these complex functions getting averaged (blurred) out. Many so-called mysteries of quantum physics can be laid at this door. It is as if a literary text in its ur-language is inaccessible, available to us only in one or another translation.

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In Orbit by Dave Campbell. CC-BY-NC-ND-2.0 via limowreck666 Flickr.

What we understand by a particle such as an electron, defined as a certain lump of mass, charge, and spin angular momentum and recognized as such by our electron detectors is not how it is for the underlying reality. Our best current understanding in terms of quantum field theory is that there is a complex electron field (as there is for a proton or any other entity), a unit of its excitation realized as an electron in the detector. The field itself exists over all space and time, these being “mere” markers or parameters for describing the field function and not locations where the electron is at an instant as had been understood ever since Newton.

Along with the electron, nearly all the elementary particles that make up our Universe manifest as particles in the classical limit. Only two, electrically neutral, zero mass bosons (a term used for particles with integer values of spin angular momentum in terms of the fundamental quantum called Planck’s constant) that describe electromagnetism and gravitation are realized as classical electric and magnetic or gravitational fields. The very words particle and wave, as with position and momentum, are meaningful only in the classical limit. The underlying reality itself is indifferent to them even though, as with languages, we have to grasp it in terms of one or the other representation and in this classical limit.

The history of physics may be seen as progressively separating what are incidental markers or parameters used for keeping track through various representations from what is essential to the physics itself. Some of this is immediate; others require more sophisticated understanding that may seem at odds with (classical) common sense and experience. As long as that is kept clearly in mind, many mysteries and paradoxes are dispelled, seen as artifacts of our pushing our models and language too far and “identifying” them with the underlying reality, one in principle out of reach. We hope our models and pictures get progressively better, approaching that underlying reality as an asymptote, but they will never become one with it.

Headline Image credit: Milky Way Rising over Hilo by Bill Shupp. CC-BY-2.0 via shupp Flickr

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24. The longest night of the year

The winter solstice settles on 21 December this year, which means it’s the day with the least amount of sunlight. It’s the official first day of winter, although people have been braving the cold for weeks, huddled in coats and scarves and probably wool socks. It’s easy to pass over the winter solstice because of the holidays; however, many traditions center around the solstices and equinoxes, and even Christmas has borrowed some ideas from the midwinter celebration. Below are a few facts about the winter solstice and the influence it has had on religion.

1.   The winter solstice occurs when the sun at noon is in its lowest position in the sky, which puts it over the Tropic of Capricorn (22-23 December).

2.   The astronomical solstice is 21 December, but midwinter or Yule covers a few weeks during the time of the solstice. During medieval times, this period would stretch from the feast of St. Nicholas (6 December) and Christmas Day, then from Christmas to Epiphany or Candlemas.

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Winter. Public domain via Pixabay.

3.   It is most likely untrue that Christmas is the birth-date of Christ. However, it was likely set on 25 December to coincide with the already well-established Pagan holidays. In ancient times, the winter solstice was celebrated as the birthday of the two gods Sol Invictus (the invincible sun) and Mithras.

4.   In contemporary Paganism, Yule celebrates the rebirth of the sun with the winter solstice, as it is the darkest time of the year with the days get longer after the solstice.

5.   The Christmas traditions of gift-giving, candles, mistletoe, evergreens, holly, yule logs, Old Father Time, red and white colors, and others all come from Latin and Germanic yuletide celebrations. The word “yule” is thought to have originated from the Anglo-Saxon word for “yoke,” although it is possible it is connected to the words for sun in Cornish and Breton.

6.   “Calendar customs are cultural expressions of repetitive seasonal rhythms.” Generally, holidays and customs follow along the changing of the seasons. Midsummer and midwinter especially pair together as the longest day and longest night of the year.

Headline image credit: Winter forest. Public domain via Pixabay.

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25. The shape of our galaxy

Many of you have likely seen the beautiful grand spiral galaxies captured by the likes of the Hubble space telescope. Images such as those below of the Pinwheel and Whirlpool galaxies display long striking spiral arms that wind into their centres. These huge bodies represent a collection of many billions of stars rotating around the centre at hundreds of kilometers per second. Also contained within is a tremendous amount of gas and dust, not much different from that found here on Earth, seen as dark patches on the otherwise bright galactic disc.

Pinwheel and whirlpool spiral galaxies, a.k.a. M101 and M51:

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Messier 101. Photo by NASA, ESA, K. Kuntz (JHU), F. Bresolin (University of Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (University of Illinois, Urbana), and STScI
Pinwheel and whirlpool spiral galaxies, a.k.a. M101 and M51.
M51. Photo by NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA).

Yet, rather embarrassingly, whilst we have many remarkable images of a veritable zoo of galaxies from across the Universe, we have surprisingly little knowledge of the appearance and structure of our own galaxy (the Milky Way). We do not know with certainty for example how many spiral arms there are. Does it have two, four, or no clear structure? Is there an inner bar (a long thin concentration of stars and gas), and if so does it rotate with the arms, or faster than them? Unfortunately we cannot simply take a picture from outside the galaxy as we can with those above, even if we could travel at the speed of light it would take tens of thousands of years to get far away enough to get a good picture!

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The current standard artists impression of the Milky Way. (Churchwell E. et al., 2009, PASP, 121, 213)
A diagram of the supposed arm and bar features.

The main difficulty comes from that we are located inside the disc of our galaxy. Just as we cannot know what the exterior of a building looks like if we are stuck inside it, we cannot get a good picture of what our own galaxy looks like from the Earth’s position. To build a map of our galaxy we rely on measuring the speeds of stars and gas, which we then convert to distances by making some assumptions of the structure. However the uncertainty in these distances is high, and despite a multitude of measurements we have no resounding consensus on the exact shape of our galaxy.

Movie showing how spiral arms (left) appear in velocity space (right).
Movie showing how spiral arms (left) appear in velocity space (right).

There is, however, a way around this problem. Instead of trying to calculate distances, we can simply look at the speed of the observed material in the galaxy. The movie above shows the underlying concept. By measuring the speed of material along the line of sight from where the Earth is located in the galaxy, you built up a pseudo-map of the structure. In this example the grey disc is the structure you would see if the galaxy were a featureless disc. If we then superimpose some arm features, where the amount of stars and gas is greater than that in the rest of the galaxy, we see the arms clearly appear in our velocity map. Maps of this kind exist for our galaxy, with those for hydrogen and carbon monoxide (shown below) gas displaying the best arm features.

CO emission map in velocity-line of sight space, showing clear spiral arm features (labeled) from Dame et al. (2001).
CO emission map in velocity-line of sight space, showing clear spiral arm features (labeled) from Dame T. M., Hartmann D., Thaddeus P., 2001, ApJ, 547,792

This may appear the problem is solved; we can simply trace the arm features and map them back onto a top-down map. Unfortunately doing so introduces the problems as measuring distances in the first place, and there is no single solution for mapping material from velocity to position space.

A different approach is to try and reproduce the map shown above by making informed estimates of what we believe the galaxy may look like. If we choose some top-down structure that re-creates the velocity map shown above, that we have observed directly from here on Earth, then we can assume the top-down map is also a reasonable map of the Milky Way.

Our work then began on a large number of simulations investigating the many different possibilities for the shape of the galaxy, investigating such parameters as the number of arms and speed of the bar. Care had to be taken with creating the velocity map, as what is actually measured by observations is the emission of the gas (akin to temperature). This can be absorbed and re-emitted by any additional gas the emission may pass through en route to the Earth.

In the two videos below are our best-fitting maps found for a two armed and four-armed model. Two arms tend not to produce enough structure, while the four-armed models can reproduce many of the features. Unfortunately it is very difficult to match all the features at the same time. This suggests that the arms of the galaxy may be of some irregular shape, and are not well encompassed by some regular, symmetric spiral pattern. This still leaves the question somewhat open, but also informs us that we need to investigate more irregular shapes and perhaps more complex physical processes to finally build a perfect top-down map of our galaxy.

Two-armed galaxy:

Four-armed galaxy:

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