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2013-05-23 13:18:34 (9 comments, 12 reshares, 54 +1s)

The Inbetweeners

Yesterday I mentioned the possibility that a mid-sized black hole might explain why the Trapezium cluster is gravitationally bound.  If such an black hole were discovered it would be a really big deal.

We know that black holes exist, but they seem to come in only two sizes: stellar and supermassive.  Stellar black holes are formed when large stars reach the end of their life and their core collapses.  They typically mass less than 20 solar masses.  Supermassive black holes lie at the heart of galaxies.  They form during a galaxy’s youth and can be a million solar masses or more.  

Between these two extremes should be intermediate mass black holes (IMBHs).  These would be hundreds or thousands of solar masses.  Too large to have formed from a single star, but not a supermassive heart of a galaxy.  An intermediate black hole could form from astellar ma... more »

2013-05-22 14:07:45 (14 comments, 13 reshares, 57 +1s)

Four of a Kind

One of the most popular constellations is Orion the hunter.  In the sword of Orion, just below the belt is a nebula known as the Orion Nebula.  This nebula is a stellar nursery about 1300 light years away.  At the heart of the Orion Nebula is a small cluster of very bright stars known as the Trapezium Cluster.  Because Trapezium is bright and reasonably close to us, we’re able to make very precise measurements of the stars’ speed and motion.  What we find is a bit of a puzzle.

In a small telescope these look like four individual stars.  These are formally known as Theta1 Orionis A, B, C, and D.  Even under high resolution they look like single stars, as you can see in the Hubble image below (http://goo.gl/FGGSr).  Under closer examination we find that C is a binary star, A is a triple star, and B is a quadruple system.  So Trapezium is actually acluster of m... more »

2013-05-21 15:48:37 (10 comments, 9 reshares, 29 +1s)

The Rise and Fall of Supersymmetry. Come see what I really think about SUSY, and why it's time to start hammering those nails into the coffin.

2013-05-21 13:37:46 (6 comments, 15 reshares, 41 +1s)

Light Me Up

One of the properties of atoms and molecules is that they interact with light in an interesting way.  If you heat up atoms or molecules in a gas, they will give off light.  But they only give off light at specific wavelengths (colors).  

The particular colors they emit depends on the type of atom or molecule it is.  So one type of atom might give off red, orange and blue, while another might give off yellow and green.  We can look at the full range of colors a particular atom emits, which is known as an emission spectrum.  You can see an example of such a spectrum in the figure below (http://goo.gl/SCu5D).

If you put a cool gas in front of a light source you get what’s known as an absorption spectrum.  Basically this looks like a full rainbow of colors with dark lines at particular wavelengths where the gas absorbs that color.  The colors a coolgas absor... more »

2013-05-20 17:04:19 (89 comments, 47 reshares, 140 +1s)

Evidence that Demands a Verdict

There’s a popular picture traversing the net recently that states 97% of climate scientists believe that anthropogenic global warming is true.  More specifically, that of peer reviewed climate research papers, of the ones that made a statement on the cause of global warming, 97% agreed that humanity was the cause.

You can imagine the lively discussions it induced.  

There are certain areas of science that people find deeply controversial.  In climate science it’s global warming.  In biology, it’s evolution.  In astrophysics it’s the big bang, or to a lesser degree things like dark matter.  The experts in these fields don’t find these controversial at all.  The big bang happened, evolution is real, and humans are a principal cause of global warming.  

The researchers in these fields have moved beyond thosebasic facts and a... more »

2013-05-19 14:31:56 (25 comments, 91 reshares, 242 +1s)

The Attraction of Curves

Newton's laws of motion and gravity predicted the motions of the planets almost perfectly. Newton's laws are so accurate that we use them to accurately send robotic probes to Mars and other planets, but Newton's laws aren't perfect. The motion of some planets differ very slightly from Newton's predictions. In the case of Uranus, its small deviation led to the discovery of Neptune. In the case of Mercury, however, its small deviation led to a completely new understanding of gravity. 

Newton's law of gravity states that objects are attracted to each other by gravity, and that the amount of attraction decreases the farther apart they are (what is known as an inverse square relationship). As a result of this force, the planets should move around the Sun in elliptical paths. Because of the gravitational pull of the other planets, the... more »

2013-05-18 13:31:38 (18 comments, 14 reshares, 64 +1s)

Losing Direction

The Kepler spacecraft is in trouble.  Launched in 2009, Kepler was intended as a “planet hunter” telescope.  It finds planets by observing stars for long periods of time.  To make long observations, Kepler needs to be able to point in the same direction very precisely, and it must be able to adjust its direction if it starts to drift.  So how do you keep a telescope oriented?

On Earth, a telescope can be mounted to the ground, and any change in direction can be made by orienting the telescope relative to its mount on the ground.  But for a space telescope there is nothing to mount it to.  This means there are only two ways to adjust the orientation of a space telescope: thrusters and gyroscopes.  

Thrusters are basically small rockets.  They release a small amount of propellent, and the telescope moves a bit in the opposite direction. It’s Newto... more »

2013-05-17 12:58:49 (32 comments, 30 reshares, 70 +1s)

It Goes to Eleven

A few years ago a research team measured the force of gravity over very small distances (http://arxiv.org/abs/0802.2350).  Their result places very stringent constraints on the space-time structure of our universe. Either the universe consists of only the four dimensions we see around us, or else all dimensions beyond those four must be very small, no more than about 10 microns, roughly one-tenth the width of a human hair.   What, you might ask, does proving Newton right (yet again!) have to do with hyperdimensional physics? Quite a lot, it turns out. 

We look around and see the usual dimensions of length, width and depth as we move forward through the dimension of time at the rate of one second per second, and it all makes sense to us. However string theory (or more properly its offspring, M-theory) says that although we may seem to live in these fourdi... more »

2013-05-16 12:54:18 (13 comments, 17 reshares, 56 +1s)

X Factor

Solar flares are in the news recently, mainly focused on four recent x-class solar flares this week.  You can see images of these flares in the image below (http://goo.gl/LjHdG).  So why all the buzz?

A solar flare is an intense burst of energy released at the surface of the Sun.  It is caused by a process known as magnetic reconnection.  The rotation of the Sun occurs at different rates depending on latitude.  It has a rotational period of about 25 days at its equator, but about 34 days near the poles.  This means the equatorial regions of the Sun rotate faster than the polar regions.  Because of this differential rotation, the magnetic field of the Sun is twisted, so that over time the field lines of the magnetic field gradually wrap around the Sun.

You can visualize a magnetic field by thinking of field lines running from the North pole to the Southpole. ... more »

2013-05-15 15:01:01 (6 comments, 10 reshares, 41 +1s)

It’s a Gas

Stars form within large clouds of gas and dust known as stellar nurseries.  Of course, when a star forms, that leaves less gas and dust to form other stars.  So you can do a bit of simple math concerning star formation.  Take the rate at which new stars form in a galaxy (and their typical mass), compare that to the amount of gas and dust a galaxy has, and you can estimate the time over which stars can form.  

For a spiral galaxy such as the Milky Way, this calculation tells us that, at the given rate of star formation, it can only keep producing stars for about a billion years.  This raises a bit of a puzzle, because the Milky Way is far older than a billion years, so how does it have enough gas and dust to keep producing stars?  

Part of it comes from the gas and dust given off by supernovas, but that isn’t sufficient to keep things going overbillions ... more »

2013-05-14 14:11:49 (13 comments, 10 reshares, 61 +1s)

Little Green Men

In 1967 a PhD student named Jocelyn Bell detected a radio signal with an odd regularity.  Patterns can be heard in all sorts of radio signals, but this particular signal was unusual in that it was a pulse with a period of 1.33 seconds.  You can see this pattern in the figure below (http://goo.gl/I4NMJ), and you can hear what the signal sounds like here: http://goo.gl/I7L0f.

Together with her advisor Antony Hewish, they found that the signal came from the same location in the sky, and followed sidereal time, which meant it was not caused by some terrestrial source.  They half jokingly referred to the signal as LGM-1, where LGM stood for "Little Green Men".  The signal was so incredibly regular that the idea that the signal was produced by an alien intelligence crossed their minds.

Soon other similar signals were discovered, and it wascle... more »

2013-05-13 14:46:20 (39 comments, 34 reshares, 108 +1s)

Non-Singular Black Holes

The basic model of a black hole can be summed up as follows: gravity wins. The root cause of all black holes—be they tiny primordial black holes, solar mass black holes, or supermassive galactic black holes—is gravity. Squeeze enough mass into a small enough volume and gravity does the rest.

The problem (at least according to general relativity) is that gravity does its job too well. Once matter enters a black hole, it simply cannot resist the pull of gravity. As a result all the matter within a black hole is squeezed down to a point of zero volume and infinite density, known as a singularity.

Black hole singularities have long been the bugaboo of gravitational physics. They cause several problems, not the least of which is that the laws of physics as we understand them break down near the singularity. As a result there has been a lot ofres... more »

2013-05-12 14:30:05 (14 comments, 16 reshares, 39 +1s)

Science and non-science

Last week was the end of term at RIT, and this week is finals.  With everything going on I haven't had time to write an actual astrophysics post for today.  So this post is a bit different.  It's about a video that has gone viral recently. 

The video (below) is on RIT's Escharian Stairwell.  The Escharian Stairwell is a stairwell that loops back upon itself.  So if you walk up a flight of stairs you find yourself back where you started.  It's inspired by M. C. Escher's Ascending and Descending.  At this point you probably recognize that the stairwell is nonsense.  The video was created as the project of an RIT graduate student.  It is well done, but clearly not real.  Surprisingly (or perhaps not surprisingly) many people think it is.

I've watched this project unfold because Kevin in the video is my friend+Kevin Sch... more »

2013-05-11 12:58:05 (8 comments, 6 reshares, 41 +1s)

Measuring the Sun

There's been lots of talk about the annular eclipse that occurred yesterday, but unless you happen to live in Australia, you probably didn't get a chance to see it.  You can, however make your own solar observation to measure the size of the Sun. This experiment uses the principle of parallax, and all you need is a sunny window, some cardboard, a pencil, and a tape measure.

Start with a sunny window, and block off as much of the light as you can, except for an area you will over with a piece of cardboard (or poster board). You don't have to block all the light, but the more you block off, the easier it will be do to the experiment. Then poke a small hole in the cardboard and put in into position. As a result, you should have a single beam of light which shines through the hole. If you move your hand closer or farther away in the beam, you should... more »

2013-05-10 14:22:28 (18 comments, 14 reshares, 47 +1s)

And Yet It Moves

A famous story in the history of science is that of the trial of Galileo Galilei. Galileo believed that the Earth moved around the Sun, but this conflicted with the theological position of the Catholic Church, which held that the Earth was fixed in the center of the universe. This conflict came to a head when Galileo was put on trial, and was forced to renounce his assertion that the Earth moved around the Sun. As the story goes, after making his public renouncement Galileo muttered under his breath "Eppur si muove!" which in Italian means "And yet it moves!"

There's no contemporary evidence that Galileo actually said those words, but it makes for a good story. It also exemplifies the frustration Galileo felt toward Church officials. Galileo had good reason to believe the Earth moved around the Sun. He had observed the phases of Venus,... more »

2013-05-09 13:57:40 (9 comments, 9 reshares, 51 +1s)

Heart of Darkness

Star formation within a galaxy is a complex process.  We have models of galaxy formation, but one of the difficulties with these models has been that they predict a greater formation of stars in large galaxies than we observe.  This would seem to indicate that there is some mechanism that hinders star formation within large galaxies.  Basically at some point in the galaxy’s formation there must be something that pushes gas out of the galaxy, preventing it from forming into stellar nurseries.

One proposed mechanism is the presence of supernova.  Larger galaxies are more likely to have more supernova, and the tremendous luminosity of these supernova would tend to push gas out and away from the galaxy.  If you do some calculations, though, you find that while that the larger the galaxy the harder it is for supernova to push gas out of the galaxy.  Thismeans t... more »

2013-05-08 14:41:43 (11 comments, 10 reshares, 54 +1s)

Massive Speed

We now know that most galaxies have a supermassive black hole in their center.  One of the ways to determine the mass is called reverberation mapping.  By looking at variations in the brightness of active galactic nuclei, you can determine the size of the black hole.  But we can only do this for about 40 galaxies, so it would be nice to have another way to determine black hole mass.  It turns out there is, using a relation known as the M-sigma relation.  

Spiral galaxies such as ours are basically a flat disk with a central bulge.  The central bulge is affected more by the gravity of the central black hole, and less by things like dark matter.  This means the speeds of stars in the central bulge are similar to the speeds of planets in a solar system (astronomers would say their motion is Keplerian).  This means that the stars closer to the black hole orbitgalacti... more »

2013-05-07 14:29:32 (8 comments, 32 reshares, 92 +1s)

Star Light, Star Bright

The Sun is a star like many others. It is special to us because it provides Earth with light and heat, but on a cosmic scale our Sun is an average, rather smallish star. How we came to understand this fact is a story with origins in the ancient past. 

For the earliest astronomers, the sky contained three things: the Sun, the Moon, and the stars. The Sun and Moon were great disks of light which could be used to predict the seasons, but the stars were tiny points of light in the velvet expanse of night. Most ancient cultures noticed that five stars appeared to move relative to the vast expanse of stars. The Latin name for these "wandering stars" was asteres planetai, from which we get the name planets. These five planets - Mercury, Venus, Mars, Jupiter and Saturn - were seen as special stars, and together with the Sun and Moon, they were seen to... more »

2013-05-06 13:56:10 (22 comments, 20 reshares, 63 +1s)

Sahara Wind

The figure below is a temperature map of the exoplanet HD 189733b.  This planet is a Jupiter-type planet that orbits very close to its parent star, orbiting about once every 53 hours.  Because of its short period, and relatively close distance (about 60 light years), we’ve been able to measure its surface temperature in the infrared.  The result is the map below (http://goo.gl/hy3VN).

The image shows the atmospheric temperature centered at the longitude facing the parent star.  It is clear that the hottest region is not the region directly facing the star, but the region about 30 degrees to the right, which is very interesting.

The planet is so close to its star that it should be tidally locked.  This means the same side of the planet faces the star all the time.  This is similar to the way the Moon is tidally locked to the Earth, and thus alwaysshows t... more »

2013-05-05 14:06:43 (13 comments, 5 reshares, 38 +1s)

Take Me Out to the Nano Lab

When most people think of a scientist they usually picture a guy who looks like Einstein in a lab coat. Admittedly that does hit close to home for a some, but for most scientists it's way off base. It would be just as accurate to imagine that all baseball players look like Hank Aaron in a Yankee's uniform.

What most people don't picture when they think of scientists is a sports team, yet the similarities are striking. Most scientists don't work alone, but rather in research groups. Just like a sports team these groups have their superstars, their solid supporting members, and their rookies. Just as a baseball team competes for prestige and ticket sales, research groups compete for status and research grants.

The analogy also highlights less noble aspects of athletes and scientists. Every sport has its history of less than... more »

2013-05-04 12:32:08 (108 comments, 28 reshares, 140 +1s)

Contact

Aliens are probably the most common topic of science fiction.  They are typically an extension of our hopes and fears.  Wise parental figures, evil enemies, noble savages, fierce predators.  They are often physically quite similar to us, with a bipedal gait, opposable thumbs,etc.  We dream of life on other worlds.  Reaching out to the stars and meeting an alien intelligence.  But is that likely, or even possible.

The difficulty with that question is that we currently only have one example of life in the universe, and that is us, the commonly descended family of life on Earth.  Beyond that, there is a quite a bit of guesswork.  It is at this point that the Drake equation is often invoked.

The Drake equation is often interpreted as a way to calculate the number of intelligent civilizations in the galaxy.  It was originally proposed at the first SETIconferen... more »

2013-05-03 19:38:40 (56 comments, 23 reshares, 116 +1s)

Mirror Mirror

The idea of parallel worlds is widely used in science fiction.  Most often this alternate world is either populated by our evil doppelgangers, or the alternate universe is just slightly different from ours, such as having zeppelins in a modern city.  Then there is the “alternate history” fiction, where their world is identical except for a key moment in history.  Lincoln survived, Harold Godwinson won the battle of Hastings, etc.  

Perhaps the earliest example of alternate universes in physics comes from the 1957 paper (DOI: 10.1103/RevModPhys.29.454) by Hugh Everett titled “Relative State Formulation of Quantum Mechanics.”  Everett’s paper was an attempt to eliminate the need for an “observer” in quantum mechanics.  

Although it is a well tested theory, quantum mechanics can be hard to wrap your head around.  As the theory wasdeveloped, a standar... more »

2013-05-02 14:13:44 (20 comments, 31 reshares, 130 +1s)

Can’t Stop the Signal

In 1873 Jules Verne’s Around the World in 80 Days was published, detailing an epic adventure of a race around the world.  In 1890, Nellie Bly was the first person to achieve this feat, travelling the globe in only 72 days.  A century ago, travelling from one end of the Earth to the other still took more than a month, but communication between the ends of the Earth could occur within hours due to wireless telegraphy.

In science fiction a similar issue occurs.  Even the closest stars are light years away, so communication between them by light could take decades.  If you want a galactic empire spanning thousands of light years, it would be useful to have some way to communicate with them within hours if not less.  It is out of this need that the ansible is often invoked.

The term ansible was first used by Ursula K. Le Guin, but waspopulari... more »

2013-05-01 14:10:44 (22 comments, 17 reshares, 91 +1s)

Still Alive

Probably the most popular representation of a wormhole in science fiction is the stargate from the franchise of the same name.  Within the franchise the stargates are described as utilizing wormholes to allow travel between various habitable worlds.  However the behavior of the stargate system is much more like a teleportation device, where matter is dematerialized at one stargate portal and re-materialized at the other end.  Similar gateways have been used in a range of science fiction stories, such as Carl Sagan’s Contact, the Star Trek episode “City on the Edge of Forever”, and Heinlein’s Tunnel in the Sky.  Similar concepts appear in fantasy stories as well, such as the magic door in Howl’s Moving Castle.

A better example of a wormhole can be seen in the video game Portal.  In this game a portal gun allows you to place two ends of a wormhole ondifferent wall... more »

2013-04-30 14:03:01 (20 comments, 34 reshares, 119 +1s)

Make It So

In the popular science fiction franchise Star Trek, there are two ways in which a ship can move.  Impulse engines, and warp drive.  Impulse engines actually exist.  Impulse is just a physics term for applying a force over a period of time, so impulse engine is just a fancy term for rockets.  In the franchise they are usually assume to be some kind of plasma rocket, but they are still just rockets.  In fact, any engine that applies a force over time is technically an impulse engine.  So the next time you climb into your car you can “engage impulse engine”.

Warp drive is something entirely different.  It allows starships to travel among the stars much faster than light, so it is clearly not conventional physics.  As its name implies, it seems to rely on warping space to allow for faster than light travel.  It is never entirely clear how it works beyond thefact that it... more »

2013-04-29 16:11:21 (41 comments, 27 reshares, 130 +1s)

There and Back Again

When someone mentions time machines, you might think of fantastical machines such as Dr. Who's TARDIS or the DeLorean in Back to the Future, but several physicists have made a serious study of time machines.  Most of this work focuses on “what if” scenarios, which are really about testing the limits of a particular theoretical model, rather than actually engineering a device that can travel to the past.  

The physics of time travel is based upon general relativity.  If you've ever taken a physics course you might remember that the motion of objects is due to forces acting on them. That is, by pushing or pulling on them—either directly or by gravitational or electric fields—you can cause them to move. This is Newton's physics, where objects fall because a gravitational force acts upon them. 

But Einstein had a different wayof looking ... more »

2013-04-28 14:27:41 (20 comments, 14 reshares, 90 +1s)

Science Fiction, Science Fact

While fantastical stories have been with us as long as we’ve been human, in the early 1800s a new type of story appeared.  Often Mary Shelly’s Frankenstein is named as the first example of this genre.  Also known as The Modern Prometheus, it gives us the tale of a mad scientist who creates a creature from alchemy and science.  By the late 1800s H. G. Wells wrote tales of The Time Machine, and an alien invasion with The War of the Worlds, and Jules Verne gave us adventure stories of an atomic powered submarine in 20,000 Leagues Under the Sea, and the first astronauts in From the Earth to the Moon.  

It’s not surprising that the earliest works of science fiction were about time travel, space aliens and starships.  We love dreaming of new horizons, and science fiction can create entire tales from the the mere whiff of scientific possibility. This can ... more »

2013-04-27 13:59:20 (25 comments, 38 reshares, 106 +1s)

Passing the Test

Recently popular-science websites have been buzzing with news of a new pulsar putting Einstein’s theory of gravity to its greatest test yet.  In particular, some tout it as a test of alternatives to general relativity.  While the attention this work has gotten in the press implies this is a new breakthrough, that’s not quite the case.  So what’s the real deal on these latest findings?

The results have been recently published in Science (doi: 10.1126/science.1233232), but you can also find a version of the article on the arXiv (http://goo.gl/8pVhH).  In the paper the team presents observations of a binary system known as PSR J0348+0432.  You can see this system in the lower right of the figure below, compared with PSR J0737-3039A/B, which consists of two pulsars, and PSR B1913+16, also known as Hulse-Taylor or H-T.

The Hulse-Taylor system isperhaps th... more »

2013-04-26 14:21:29 (54 comments, 109 reshares, 310 +1s)

Sim Universe

As computers have grown ever more powerful, astronomers and astrophysicists have increasingly used computers to model the complex systems they study.  This can range from modelling the motions of planetary bodies in our solar system, to simulating the convection of plasma in the depth of a star.  Perhaps the most ambitious computer modeling project, however, is the Millenium Project at the Max Planck Institute.  

The Millenium Project is an effort to model the entire universe computationally.  The initial model simulated a cubic region of space about 2 billion light years across.  In this volume was about 10 billion clumps of dark matter, each clump being about a billion solar masses.  To this was added about 20 million galaxies.  

You can see an image of the result below (http://goo.gl/86Jju).  One of the things that stands out in this image isthat th... more »

2013-04-25 13:55:02 (11 comments, 34 reshares, 81 +1s)

Hubble’s Tuning Fork

Edwin Hubble is perhaps most famous for discovering a relationship between the distance of a galaxy and the speed at which a galaxy moves away from us.  This relation is now known as Hubble’s Law, and is evidence for the expansion of the universe.  But Hubble’s primary interest was in galactic nebulae (what we now just call galaxies).

Hubble was a consummate astronomer, and made some of the best galactic observations of his day.  Over time he noticed that while galaxies could have all sorts of different shapes, they could be grouped into three large classes:  ellipticals, spirals, and irregular.  Hubble further organized galaxies into sub-categories, and in 1926 proposed a classification scheme known as the Hubble tuning fork. 

You can see this classification in the image below (http://goo.gl/T5GpD).  You can see that starting with analmost spher... more »

2013-04-24 14:21:47 (19 comments, 39 reshares, 80 +1s)

Never a Miscommunication

The Earth and Moon are slowly moving apart.  The moon’s distance from the Earth is not constant, because the Moon’s orbit is not perfectly circular.  Over the course of a month the moon comes as close as 363,000 km and as far as 405,000 km due to the eccentricity of its orbit.  However its average distance is slowly increasing.

We have very precise measurements of the Moon’s distance made by laser ranging.  Retroreflectors were placed on the Moon during the Apollo missions, around the time when the picture below was taken (http://goo.gl/Wnzrn).   The retroreflectors let us bounce laser beams off the Moon, which lets us measure the distance of the Moon to within millimeters.  What we’ve found after decades of observation is that the average distance of the Moon is increasing at a rate of about 3.8 centimeters per year.  Not much compared tothe range of i... more »

2013-04-23 14:02:05 (22 comments, 65 reshares, 138 +1s)

Hydrogen, Helium, Metal

There’s an old joke that the astronomer’s periodic table consists of three elements: hydrogen, helium, and metal.  It’s a nice joke, but when you understand how little of matter in the universe is “metal”, you can understand why astronomers focus on hydrogen and helium.  

You can see this in the figure below, which gives the relative abundance of different elements by area, the larger the square, the more of that particular element there is.  As you can see, most of the elements of the periodic table are too small to even appear.  The few others that do show up are dwarfed by the hydrogen and helium squares.  

Where the joke is accurate is in the fact that astronomers often refer to all the elements beyond helium as metals.  This is is why we use terminology as the metallicity of a star.  Since the “metals” of a starincludes everything ... more »

2013-04-22 15:13:09 (7 comments, 5 reshares, 28 +1s)

NASA Outreach

You may have heard about NASA's budget woes and how that impacts most of their outreach programs.  It means we not only lose programs such as the annual +NASA Jet Propulsion Laboratory open house and +Pamela Gay's +CosmoQuest, but also programs such as the one I worked with this past weekend.  It is a project called NASA Science and Technology on the Family Calendar.

It is a collaboration between +NASA, +Rochester Institute of Technology, and the Rochester Museum and Science Center where kids get to develop demonstrations and displays for their science center.  It's a great example of bottom up (rather than top down) science outreach.  Science driven by the questions and interests of kids themselves, rather than being dictated by teachers and scientists.

The overall topic for this weekend's project was "Earth From Space". So ... more »

2013-04-21 13:22:38 (30 comments, 28 reshares, 165 +1s)

Our Universe

If you are fortunate, you have come across a book or two that has deeply impacted your life.  One such book for me is by Roy A. Gallant: The National Geographic Picture Atlas of Our Universe.  

I was interested in astronomy and things science at a young age, and in the Fall of 1980 a new series on astronomy called Cosmos began to air.  Every Sunday evening that Fall I watched Carl Sagan explain the universe to me.  The last episode of Cosmos aired on the 21st of December.  Then on the 25th, my Grandmother gave me the book you see below.

It’s hard to describe the impact this book had on my childhood.  It is a book that changed my view of the universe.  Every page is rich with color images and diagrams.  The writing is clear enough for a child, but not written in a condescending or belittling tone.  It contains facts and figures on everythingfrom the s... more »

2013-04-20 14:00:20 (37 comments, 93 reshares, 269 +1s)

Fiat Lux

In 1671, Isaac Newton submitted a letter to the the Royal Society outlining a new theory of light and color. While Newton is probably most famous for his theory of gravity—and the mythical apple—he was also deeply interested in the nature of light, and made one of the first detailed studies of the properties of light. The work he describes in this 1671 paper is so brilliantly simple you can do it at home. All you need is some sunlight and a couple of prisms.

In Newton's time it was already well known that light passing through a prism would produce a spectrum of colors. It was generally thought that the color must somehow be contained within the prism glass, and when light passed through a prism it would be tinted various colors. Newton was able to clearly show this was not the case. To show this, Newton sealed off a room from light except for a small hole in awin... more »

2013-04-19 16:48:32 (11 comments, 19 reshares, 64 +1s)

Brown Dwarf Desert

A brown dwarf is larger than a planet, but not large enough to be considered a star.  Stars undergo fusion in their cores, but a brown dwarf lacks the mass necessary to initiate fusion.  At the same time, they are more like stars than planets, and can have at atmospheric temperature of 2000 K.  So these objects occupy a middle ground between star and planet.  

Historically, brown dwarfs have been difficult to observe.  They are small and relatively cool, which makes them fairly dim in the range of visible light.  However with the rise infrared astronomy and all-sky surveys these brown dwarfs are now fairly easy to detect.  This is particularly true for brown dwarfs which are companions to other stars, since the methods used to discover planets would also easily detect brown dwarfs.

This has given rise to a bit of a mystery, known as the browndwarf ... more »

2013-04-18 14:06:53 (31 comments, 51 reshares, 82 +1s)

The Four Elements

Around 450 BC, the Greek philosopher Empedocles wrote that the world was comprised of four things: earth, air, fire and water. Plato referred to them as the four elements. These were not elements in the modern sense, but rather essences that gave everything their physical properties. The idea that everything was made of these fundamental elements had a deep influence on early Western science. It was a central aspect of alchemy until Robert Boyle demonstrated there were more than four elements in 1661. The four elements also connected to the four humours of the human body, which formed a basis of Western medicine until the 1800s.

Over the past two centuries, we have gained a much better understanding of the atomic elements and how they have formed. One of the things we have learned is that we—and every other living thing on Earth—are made up mostly of fourele... more »

2013-04-17 16:48:15 (26 comments, 14 reshares, 43 +1s)

Mine Over Matter

Minnesota’s Soudan Underground Mine State Park is a former iron mine.  Because of the orientation of the hematite, the mine had to go deep, and by the time of its close as an active mine in 1962 they were mining more than 2000 feet below ground level.  Given its depth, and the geology of the region, the lower levels of the mine are well shielded from cosmic rays, which makes it a perfect location for sensitive experiments such as the search for dark matter.  This is why it’s the location for the Cryogenic Dark Matter Search (CDMS).  

The CDMS detectors are supercooled semiconductor detectors.  When particles interact with the semiconductor material (germanium and silicon), it causes the atoms in the material to oscillate. Just how the atoms oscillate depends on the way a particle interacts.  Most normal particles interact with the electrons in thesemicondu... more »

2013-04-16 13:18:13 (16 comments, 12 reshares, 65 +1s)

Flare Up

Back in January (http://goo.gl/eKmnJ) I wrote about a new discovery of a dramatic rise in carbon 14 (C14) in the atmosphere around 774 AD.  Carbon 14 is radioactive, and decays over time.  It is one of the ways we can date the age of living things long after they’ve died.  The reason is because carbon 14 is generated in the atmosphere when high energy particles strike nitrogen atoms in the upper atmosphere, and living thing utilize that carbon while they are alive.  Once they die the carbon 14 in them isn’t replenished, so as the carbon 14 decays it over time it gives us a measure of how long an organism has been dead.

Since the level of carbon 14 in the air varies over time, we to account for that historical change when determining the age of objects.  Currently we have a calibration table which is accurate to 1% over about 29,000 years.  While this is anaccurate ... more »

2013-04-15 14:04:52 (14 comments, 32 reshares, 62 +1s)

Wondrous Star

Mira is a red star in the constellation Cetus.  It is a variable star, meaning that its brightness changes over time.  While there are some indications that its variable nature was known in ancient times, the earliest reliable documentation of its variability comes from the late 1500s.  By the mid-1600s, astronomers had determined that Mira’s brightness varied over a period of 333 days.  The name Mira is Latin for “wondrous”, and so Mira is indeed a wondrous star.

We now know that Mira is a binary star.  The companion star, Mira B is a white dwarf, while the primary star Mira A is a 6 billion year old red giant star.  Its mass is a bit more than that of our Sun, so in many ways looking at Mira A is glimpse into the future of our own Sun.  That’s because Mira is a Sun-like star that is reaching the end of its life.  Mira was just the first star ofits kind to be ... more »

2013-04-14 17:35:02 (32 comments, 33 reshares, 128 +1s)

Astronomical Units

Yesterday I wrote about how astronomers can use the principle of parallax to measure the distance to stars. However this principle was first applied to the moon and the planets. More than 2,000 years ago Hipparchus used the parallax of the moon to measure its distance. He found that the distance to the moon was about 60 times the radius of the Earth, or about 237,000 miles. (The actual average distance is 239,000 miles.)   Earlier, Aristarchus measured the angle between the Moon and the Sun when the Moon was in its quarter phase (when half of it is illuminated from the Sun), and used trigonometry to determine that the Sun was about 20 times further away than the Moon, or about 4,740,000 miles. This distance is much lower than its actual value, but was the accepted value until at least the 1400s. 

Despite their success with the Moon and the Sun, the distancest... more »

2013-04-13 14:05:20 (54 comments, 152 reshares, 548 +1s)

Parallax View

When you look at the night sky it is easy to imagine that the stars are part of a great celestial sphere. Stars appear to be fixed in relation to each other, and they appear to move about the Earth in unison. This is why most ancient cultures imagined that the stars were a part of a sphere or shell of night, and that all the stars were the same distance away from us. This illusion occurs because even the nearest stars are very, very far away. So how is it possible to say with confidence (as I did in an earlier post) that Sirius is 8 light-years away, or that Betelgeuse is 640 light-years away? 

There are actually several methods to determine cosmic distances, and these are combined to create what is known as the cosmic distance ladder, but the oldest and most direct method uses the property of parallax. Parallax occurs when you look at an object from two slightly... more »

2013-04-12 15:05:24 (39 comments, 52 reshares, 122 +1s)

Goldilocks Zone

Earth is the one planet we know of that is well suited for life.  Of course this is a sample size of only one, and it’s a biased sample, since we’re it.  This means we should take any speculation on the existence of life on other planets with a grain of salt, but there are some things we can at least tentatively speculate on.

One of these is the possibility of liquid water on a planet.  Life on Earth can survive in a wide range of environments, but generally needs to have access to water, so it seems like a decent starting requirement for life similar to Earth life.  This means at the very least we need to consider the temperature of a planet.   

The temperature of a planet depends on several things.  Most importantly is the temperature of the star it orbits.  Red dwarf stars are smaller and cooler, so planets would need to be closer thanEarth to be... more »

2013-04-11 13:52:30 (29 comments, 20 reshares, 63 +1s)

Beyond the Farthest Star

When you look up into the night sky, you are seeing into the past. Cosmic distances are so vast that it takes time for light to travel them. Light from the closest star to Earth—the Sun—takes more than 8 minutes to reach us. After several hours that same light reaches the outer region of our solar system, where Pluto and other dwarf planets reside, but it will take more than four years for the light to reach the next nearest star. After 100 years the light from our sun has reached less than 20,000 stars. The brightest star in the night sky is Sirius, more than 8 light-years away, which means we see Sirius not as it is now, but as it was 8 years ago. 

Most of the stars we see are even further away. The constellation Orion has several bright stars. Betelgeuse, the red star at the upper shoulder of Orion, is about 640 light-years away. Rigel, thebrig... more »

2013-04-10 14:47:21 (32 comments, 26 reshares, 93 +1s)

Tower of Babble

Science is about being specific. Scientific terms such as energy, speciation and fusion have very specific meanings within a specific context. These terms often have common meanings as well. If we say that reggae music is a fusion of calypso and jazz, we don't mean it was created from calypso and jazz nuclei in the core of a star. But while words can have poetic and even multiple meanings, their scientific meanings are precise. 

This difference between scientific and general word usage can be difficult to distinguish without practice. When these two uses get mixed up, all sorts of problems occur. The word "theory" is a good example of this. Its common usage is akin to "idea" or "belief", while its scientific meaning is that of a well-validated scientific model. If something is "just a theory" (idea), it can be easily... more »

2013-04-10 19:20:01 (18 comments, 28 reshares, 72 +1s)

Black Holes, Brownian Motion

If you've ever watched dust-motes dancing in a sunbeam then you've observed Brownian motion. It is the jerky, fluttering motion of particles in fluids such as air or water. The botanist Robert Brown first described the motion in detail. He demonstrated that it was not caused by some living organism, but was never able to determine its cause. That answer came from Albert Einstein, who proved that Brownian motion was due to molecules of the fluid colliding with the Brownian particle.  Brownian motion was definitive proof of the atomic theory of matter. Even though we couldn't (at that time) see the atoms which make up matter, we could see the effect of their existence. What does all this have to do with black holes? Well it turns out black holes also undergo Brownian motion, and astronomers can use that fact to their advantage.

Within most... more »

2013-04-09 13:40:36 (13 comments, 15 reshares, 38 +1s)

Cycle of Stars

We generally think of the Sun as a steady constant, but it’s actually quite variable.  The Sun’s magnetic field varies over time, which means the activity of the Sun varies.  The earliest observation of this cycle was seen in sunspots (http://goo.gl/37vGb).  While sunspots were observed throughout history, in the early 1600s astronomers began making regular observations of sunspots, and soon discovered an 11-year cycle of high and low sunspot activity.  Over time similar variations in solar flare activity and brightness.  Thus the Sun cycles through active and quiet periods.  

In the early 1800s Joseph von Fraunhofer discovered that sunlight was not a continuous range of colors, but rather had gaps at certain wavelengths (http://goo.gl/58tZq).  These gaps are now called Fraunhofer lines, and we now know they are cause by the Sun’s atmosphere absorbingcertain wave... more »

2013-04-08 13:55:15 (13 comments, 36 reshares, 120 +1s)

Hidden Giants

In the center of most galaxies (including our own) is a supermassive black hole.  These black holes can have masses of hundreds of millions of Suns.  Some are more than a billion solar masses.  Active supermassive black holes can be extraordinarily bright.  When active, these black holes are surrounded by an accretion disk, which generates tremendous heat.  Matter streams from their polar regions, creating huge jets of material that races away at nearly the speed of light.  

How that energy is seen depends on how the galaxy (and hence the black hole) is oriented relative to us (http://goo.gl/bzJfw).  If we view the galaxy edge on, then we mainly see the jets streaming outward, which produces intense radio energy, and we see them as radio galaxies.  If the galaxy is tilted a bit toward us then we can see some of the accretion disk, which is so hot it givesoff x-r... more »

2013-04-08 00:57:04 (4 comments, 3 reshares, 9 +1s)

Hang out with +Brian Koberlein this evening to discuss astrophysics!

2013-04-07 22:26:25 (29 comments, 35 reshares, 113 +1s)

Hot Rocks

Asteroids come in a range of sizes, from hundreds of kilometers in diameter down to a meter wide and smaller.  Determining just how many asteroids there are is a challenge, because the smaller an asteroid’s size, the more difficult it is to observe.  Additionally, smaller asteroids are far more numerous than larger ones.

The size distribution of asteroids roughly follows a power law distribution.  For every 1 kilometer asteroid, there might be a hundred 100-meter ones, ten thousand 10-meter ones, and a million 1-meter ones.  Of course this relationship isn’t exact, and variations in this distribution can significantly change the numbers, particularly for smaller asteroids.  To really get a handle on the size distribution of asteroids you need to make a large survey of mid to small-sized asteroids.

For smaller asteroids, the only way to efficientlydetermin... more »