Silver and Gold: Clues to the History of Our Solar System

It's that time of year when many of us are buying gifts for our loved ones.  And there's a song from the old Rudolph the Red-Nosed Reindeer TV special that comes to mind (sung by the character Yukon Cornelius):  "Silver and gold, silver and gold.  How many wonders can one cavern hold?..."    But have you ever stopped to think about where your jewelery came from?  I don't mean how your silver and gold was mined, but how was it created?  It's much more interesting than anything you've probably imagined!

SILVER & GOLD

Gold crystal (image from Wikipedia)

First, let's go back to the birth of the Universe:  BANG!  (That was the Big Bang.)  Sometime between 10 seconds and 20 minutes from now, the first atoms will be formed (this is called Big Bang nucleosynthesis).  These first atoms were of the simplest elements in the periodic table; mostly hydrogen and some helium and lithium.  Even today, the most common elements in the Universe are hydrogen and helium.  A few hundred million years later, clouds of this material will collapse to form the first stars.  This birth is marked by the ignition of nuclear fusion: the smashing of lighter elements together to make heavier ones.  All stars start by smashing 2 hydrogen (H) atoms together to make a helium (He) atom.  Eventually, the star will start to run out of hydrogen and will start to fuse helium to make beryllium (Be) and carbon (C).  The largest stars will continue fusing atoms together until the product element is iron (Fe).  For elements lighter than iron, smashing two lighter elements together to make a heavier element will release some energy.  For elements heavier than iron, breaking an atom into two lighter atoms will release energy: this is called nuclear fission.  So, the heaviest element that any star can normally make during its life is iron.  Heavier elements like silver (Ag), gold (Au), and platinum (Pt) and many other elements can only be created in the most extreme environments such as a supernova explosion that marks the death of a star.  Therefore, the metal in our jewelery is truly a relic of a star that died before our Sun was born.

Our Sun and solar system was born from the supernova explosion of an older star that died and, in doing so, seeded the material that makes up our solar system with heavier elements (this is the nebular hypothesis).  For example, since the Earth is not a star it cannot perform nuclear fusion.  Yet the core of our planet is primarily iron and nickel and had to be made in a previous star.  This is what Carl Sagan meant in his famous quote, "We are all starstuff."


WHAT ABOUT DIAMONDS?

Diamond set into a gold ring (image from Wikipedia)

 While I'm on the topic of the exotic origins of jewelery (and many other things), let me talk a little about why our Sun may turn into a giant diamond.

First off, a diamond is made from carbon which our Sun is capable of making much later in its life (more on this in a little bit).  Carbon is everywhere around us - pretty much every molecule that isn't water in your body has at least one carbon atom in it (this is the definition of an organic compound).  What makes a diamond special from all of the other common forms of carbon is that it has a very specific crystal structure that is only formed under extreme pressure and heat.  (Any mineral that has the same chemical structure but a different crystalline organization is called a polymorph.)  So, the diamonds that are formed naturally on Earth started as a carbon deposit that transformed into a diamond under the extreme pressure and temperatures found beneath the surface of the Earth.

What does this have to do with our Sun?  Well, right now the Sun is busy turning hydrogen into helium.  It will eventually (in about 5 billion years) start making heavier elements, but only much more massive stars ever have enough oomph (enough mass to create the most extreme pressures) to fuse elements all the way up to iron.  Our Sun is not one of those stars (which is good since those massive stars live comparatively short lives).  The Sun will only be able to produce up to carbon and oxygen (O) before fusion stops and the outer layers of the Sun are blown into the interstellar medium to seed future stars and solar systems.  What is left behind is called a white dwarf composed of carbon that has been exposed to intense pressure and temperatures.  That means that the white dwarf our Sun leaves behind may very well be a diamond!

A white dwarf that could be a massive diamond has already been observed and nicknamed "Lucy" (after the Beatles song "Lucy in the Sky With Diamonds").  It is more massive than the white dwarf our Sun will leave behind, but seems to be created by the same processes we expect for our Sun.  All of this is very promising for a diamond to be the memorial for our Sun (and solar system).


WHAT DOES THIS HAVE TO DO WITH GRAVITATIONAL WAVES?

Directly, not much.  However, this past August it was confirmed that a short gamma-ray burst was the result of a kilonova, the collision of two neutron stars that releases a massive amount of energy (read more about this here and see my comments towards the end of the article).  Neutron stars are the remnants of dead stars that were much more massive than our Sun (about 10 to 40 times the mass of our Sun) that died in a supernova.  Those past supernovae would have created silver, gold, and everything heavier than iron and seeded the interstellar medium for future stars and solar systems.

These kilonova sources should produce copious amounts of gravitational waves, however, there has never been a short gamma-ray burst (like the one I mentioned above) detected close enough for LIGO to see it.  Once Advanced LIGO is complete (soon!) the closest short gamma-ray burst will be just on the edge of the distance we expect to be able to detect these kinds of gravitational waves.  But the great thing about what we do is that we really don't know how strong the gravitational waves from the actual explosion will be so they could very well be detectable in the future.

Fingers crossed!

Living LIGO's Belated 3rd Anniversary

This past Saturday, 5 October, was the 3rd anniversary of the Living LIGO blog (you can see the first ever post here).  I remember that because it also happens to be my birthday - I started this out of a desire to do something I always wanted to so what a better day to start than your own birthday.  (If you must know, I've just celebrated the 6th anniversary of turning 29.)

I know it has been a long time since I've posted.  I've been teaching at LSU and doing research at LIGO.  On paper my life looks great but the reality is that there are many details, both personal and professional, that have added up to me not being in a great place for a while.  I've been getting my jobs done but after that I've been pretty exhausted, at least mentally.  This has happened to me before, so I thought I would direct you to my thoughts on what it's like being down but getting up again anyway here.  (Also see my last section below: "A WORD OF ADVICE...".)

But there is one thought that has come up many times in the last few months:  "I'd like to write a blog post on that."  There are many different things, like continuing the series of posts I've started about methods of looking for gravitational waves or telling the story of where silver and gold come from (as in, how did it come to be on Earth).  So, I am going to dig myself out of my slump and get back on my metaphorical horse - starting now!


WHAT I DID THIS SUMMER

Let me tell you a little about what I've been doing since I've last posted.  I got to go to a large meeting called the GR20/Amaldi10 Meeting in Warsaw, Poland (where almost 850 gravity theorists and experimentalists gathered for this joint meeting) and gave 2 invited talks.  The first was a formal talk on outreach skills and media (featuring this blog) and the other was less formal and was on the benefits searching for gravitational waves can bring mankind focusing on spin-off technology (I've written about this before here).

This is a picture of the gates of the Uniwersytet Warszawski where GR20/Amaldi10 took place.

A view through the gates at my colleagues on a coffee break in the distance.

One of the best parts of meetings like this is that the meeting dinner is usually somewhere a normal person couldn't go.  Our dinner was at the in the Royal Castle in Warsaw.  And this is my husband and I on the lawn beforehand:

My husband, Derek, and I on the lawn behind the Royal Castle in Warsaw, Poland.

Just before my trip to Warsaw, I took a short holiday to Paris, France.  There was a debacle with lost luggage and then wrong luggage being delivered to us, but outside of wearing the same clothes for a few days (this is why I always pack extra underwear in my carry-on luggage), my husband and I had a great time just relaxing and wondering around.  My new phone takes panoramic pictures and this is a good one I got of the Louvre:

Panoramic view of the Louvre (Paris, France)
Click on the picture for a larger view.

Once I returned home to the United States, I had tons of work to do.  I've talked before about how LIGO has been testing its data infrastructure to prepare for Advanced LIGO here.  We are then had our 4th software engineering run; that means that I had to improve upon the gravitational wave simulation software I wrote to perform better, faster, and incorporate more features.  It was a bit stressful come the deadline, but it all got done and turned out well.


... AND THEN SCHOOL STARTED AGAIN

Then school started again.  I am teaching (at LSU) the first semester of physical science (sometimes referred to as "Physics for Poets" since it is more conceptually based than mathematically focused).  Most of my students in this class (this year my lecture has only about 100 students) are elementary education majors.  Some might think that teaching an "easy" class like this would be, well... easy.  But it is far from it.  The less math you can rely on to teach the subject matter, the better you have to be as a teacher in communicating what the math means.  Since I love challenges like this, this is one of my favorite classes to teach.  I am also team teaching a junior/senior level class on Science Methods for secondary education pre-service teachers majoring in science or math.  This class shows them how science is done by doing experiments using the scientific method, analyzing their data and reporting it in both papers and presentation (since these are the two main means that scientists communicate with each other).

At LIGO, I am working on a paper with a group of other LIGO scientists who are looking for gravitational waves from supernovae that may have occurred while LIGO and/or other gravitational wave observatories were in operation (before the advanced detector upgrade began).  And, as always, I continue to refine my gravitational wave simulation software.


A QUICK WORD OF ADVICE...

I'll be writing again soon (probably next week).  When I first started this blog, I promised you a peek into the life of a working scientist.  Lately I've been answering lots of questions about gravity and how to look for gravitational waves.  But since there has been something major going on in my life, and it kept me from writing my blog as I would have liked, I wanted to share that with you.

I am lucky since even though I know I have times when depression can get the better of me, I have wonderful support from my husband, friends, and family.  I'm not sure why, but they all seem to love me even when I can't stand to be around myself. 

For anyone reading this who has issues with depression and/or anxiety:  Don't fool yourself that everything you are feeling inside is not affecting you because you may be able to keep it together and have others think you are happy.  This will eat at you and everything you are feeling will come out sometime (and usually at the least opportune time).  If you are sad or anxious for long periods of time, even if it's on-and-off, find some help.  It is not weak to seek help (I've been told that before and it's usually by people who need help for themselves and are too afraid to get it).  It takes an inner strength to admit when you are hurting and need a hand up, an ear to listen to you, or a shoulder to cry on.  If that's not enough, talk to your doctor.  Not once has a doctor been anything but 100% supportive of me when I've gone to them seeking medical help.  NOT ONCE did they look down on me, or suggest that my feelings will pass, or that I need to "buck up".  With support and help, I've always clawed my way back to feeling like a normal person.  You can too!

Black Holes 101

Most of what I discuss on this blog has to do directly with gravitational waves.  This time I'd like to talk about one of their most talked about exotic sources: black holes.  Black holes are an exemplary source because they are highly concentrated mass.  Just add a touch of accelerated motion and gravitational waves are emitted in abundance (well, it's not quite that simple and "abundance" is a relative term, but you get the idea).  But what are the fundamental concepts that add up to the existence of black holes?  That's what we are focusing on now.


1.  Escape velocity

You've probably noticed that the harder you throw an ball straight up in the air, the higher it goes.  We also know that the farther away the ball gets from the Earth, the lower the gravitational attraction is between the ball and the Earth.  When you connect these two concepts, you can imagine that there is a speed at which you can throw the ball up and it will never come back down.  This is called the escape velocity:

We have discussed escape velocity before on this blog (specifically when discussing the conditions an object must have to be 'eaten' by a black hole).  In this equation, G is the gravitational constant, M is the mass of the 'thing' you are trying to escape, and r is the distance you are from the center of the 'thing'.  The bigger the mass of the 'thing', M, is, the faster the object must be thrown to escape it, v_e.

Going back to throwing a ball up in the air from the Earth's surface, you would need to throw that ball about 25,000 mph so that the ball would not come back to the Earth (good luck with that)!


2.  The speed of light is the universal 'speed limit'

Nothing can travel faster than the speed of light (in a vacuum), represented by c.  No matter, energy, or information about the Universe can travel faster than that.  That is pretty much the long and the short of this concept.

[Source: Knight Science Journalism at MIT blog]

This 'speed limit' comes from Einstein's special relativity and the effect of simultaneity.  Perhaps I will write a longer post about this in the future, but all that is important now is to recognize that if something needed to travel faster than the speed of light to communicate information to you, then you are never going to know about it.


3.  Light is affected by gravity

Light is both a particle and a wave.  As a particle, it has no mass.  Since gravity acts between two masses, it may be surprising that light can be affected by gravity at all!  But it does.  This effect is called gravitational lensing and I've written about this previously here. 


CONCLUSION:  How these concepts form a black hole

The simplest black hole is called a Schwarzschild black hole.  This is a black hole that has no electrical charge and is not rotating - it's just "there" meaning that there won't be anything to complicate our black hole situation.  For now, let us think of our black hole as having mass but no volume.  You can think of this as being the ultimate implosion.  Since this mass has no volume, there isn't any surface to it.  Eventually, as we get closer and closer to where the mass is centered, the escape velocity will become so large that the escape velocity will be greater than the speed of light.  And since light is indeed affected by gravity, that means that nothing will be able to escape the black hole.  We can even figure out what this distance is from the equation for escape velocity by setting v_e to the speed of light, c, and solving for r (the distance away from the mass where the escape velocity equals the speed of light):

This distance from a black hole where light will not be able to emerge from a black hole is also called the event horizon and this sphere around the black hole is what is being referred to when we talk about the size of the back hole.  For this simple Schwarzschild black hole, it is also known as the Schwarzschild radius.  You can also think of this radius as how small a mass would have to be to become a black hole.

So, how big would the Schwarzschild radius be for some things we are familiar with?  Well, for a black hole with the mass of our Sun it would be just about 3 km or about 1.9 miles.  For a black hole with the mass of the Earth it would be 8.87 mm or a little under 11/32" (0.349 in).

Lessons From My Childhood on How to Teach

One of the best parts of my job is getting to do outreach.  This is going out and teaching the public about the research that I do.  Since I love what I do and those that I encounter are usually interested in what I have to say or they wouldn't be there (like you wouldn't be reading this if you didn't want to), it is almost always a rewarding experience all around.  However, I had some childhood experiences with outreach that were, well, a little traumatic.  However, they have taught me lessons that I use every time I teach whether in the classroom, engaging the public at LIGO, or writing for you.

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"HAIR-RAISING" TRAUMA

Ever since I was a young child, I've always known that where I am now is where I wanted to be.  That is, I've always known that I wanted to be a physicist or an astronomer.  Of course, that's not what I said; I wanted to be an astronaut since that is the hero job for the physical sciences.  My family has also been supportive of me and one of my favorite things to do was go to the planetarium.  At the time, I lived outside of Pittsburgh, PA and we would go to the Buhl Planetarium (before it became part of the newer Carnegie Science Center - the building is now part of the Children's Museum of Pittsburgh).

Front entrance of the Buhl Planetarium in Pittsburgh, PA. [Source: Wikipedia]

On the fateful trip in question, I was no more than 7 or 8 years old and I was watching a demonstration in between planetarium shows with my father.  The presenter asked for a volunteer from the crowd, preferably with long fine hair.  The next thing I felt is my father's hand on my back pushing me forward.  I wasn't interested in being the center of attention, but the presenter thought that I would be perfect for the role.

She called me forward and had me stand on a plastic milk crate beside a metal dome that was bigger than my head.  She told me that I was going to have to hold on the the metal dome with one hand but I was not to do a list of things or I would get hurt.  Then I was worried.  She had me put one hand on the dome and turned the machine on.  It made a lot noise and I feel an odd tingling over my skin.  Then I was scared.  The presenter was very happy about everything and told me to shake my head.  I did so timidly.  Then she encouraged me to shake my head with more vigor.  I shook the heck out of my head so she would leave me alone and I could be done with all of this.  Then EVERYONE who is watching this demonstration WAS LAUGHING AT ME.  Then they applauded as the machine was turned off and I was helped down from my perch and left to think I was being laughed at.

The machine with the big metal dome attached to the top.  I later discovered that this is a Van de Graaff generator.  [Source: UMN Physics department]

It wasn't until I was in middle school that I figured out why everyone was laughing at me.  That machine was a Van de Graaff generator and it deposited static electricity on me.  The warnings that worried me were to prevent me from getting "zapped" and everyone was laughing at me because my hair was standing on end.  The harder I shook my head, the more the static electricity made my hair stand out.  A lot like this:

WHAT WENT WRONG?:  The presenter didn't show me what I looked like in a mirror (as is featured in the clip above) or tell me what I looked like.  I had no idea why everyone was laughing at me or what the point of the "hair raising" demonstration was.  Without this knowledge, I walked away from the experience thinking that everyone was really laughing at ME and not the effects of static electricity.

LESSON LEARNED:  If you use a volunteer in a demonstration, make sure that they understand what is happening.

I don't have many occasions where I need a volunteer for a demonstration, but when I do I make the volunteer the focus of the demonstration so that, at the very least, they walk away understanding what happened. 

Read more about how Van de Graaff generators work.

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SWINGING FOR A "BREAKTHROUGH"

When I was too young for school, I wanted to be a big girl and play school.  Even then I loved science.  One day I convinced my father to play school with me.  Using the sliding green chalk board doors on my toy box, my father taught me about the layers of the Earth.

A toy box much like the one my father used to play school with me.  [Source: It's Still Life blog]

The Earth's layers can be generalized into 4 main layers: the crust at the surface where we live, then the mantle, and finally the outer and inner cores.

Diagram showing the layers of the Earth.  [Source: About Earth blog]

I was told that the crust was very thin and the mantle is hot molten rock (magma) [note: only the mantle near the outer core is molten but the mantle under the crust is about 1000^oF so I equated that to "molten" too as a child].  I'd seen documentaries about volcanoes on television and knew what "molten rock" meant.  This completely changed the way I saw the swing set in my back yard.  Why?  Well, have you noticed the divot under the swings where you drag your feet to slow the swing to a stop?  I saw that as eating away at the crust and I was afraid that I would break through to the mantle and sink my feet into molten rock!  I know that it really isn't logical since I'd seen deeper holes before and there was nothing but dirt at the bottom, but I was a little kid and didn't think like that.  Anyway, I then was afraid of breaking through the crust if I dragged my feet and I was too chicken to jump off.  That left me sitting on the swing waiting for it to slow down on its own.  The wait took a lot of the fun out of swinging!

WHAT WENT WRONG?:  The scale of "thick" and "thin" was not established.  When I heard that the crust was thin, I defined for myself what "thin" was.  I assumed it was only as deep as I could dig through it.  What "thin" really meant is compared to the size (radius) of the Earth.

For the record, the radius of the Earth is almost 4,000 miles and the crust is up to about 22 miles.  Since 22 miles is much, much less than 4,000 miles, the crust is indeed "thin" compared to the size of the Earth!

LESSON LEARNED:  When you tell someone that something is "big" or "small", make sure you establish what you are comparing that something to, i.e. make sure you set the scale for your comparison.

I sometimes tell this story after I admonish people to always ask a scientist how big or small they think "big" or "small" are.  I tell them that I think a "big" gravitational wave, one that we would only expect to see every 10 years or so, would change the length of LIGO's 4 km (2.5 mile) long arms less than 1/1000^th the diameter of a proton (10^-18 m).   That may be "big" to me now, but to a 5-year-old me something smaller than an atom would be most certainly be considered "small". 

Q: What's the Difference Between a "Gravitational Wave" and a "Gravity Wave"?

The things that LIGO looks for are called gravitational waves (which are discussed in depth here on my blog and on the LIGO website).  That can be a mouthful, especially when having a conversation about them.  People, including us professionals, realize this and often take the shortcut of calling them "gravity waves".  It sounds so similar that this must mean the same thing, right?  Well, no!


GRAVITY WAVES ARE NOT GRAVITATIONAL WAVES

The proper technical use of gravity wave refers to waves on the interface of two fluids, which can be liquid and/or gas.  Where this boundary is disturbed, gravity will pull it down and buoyancy will push it up.  This combination of opposite push and pull creates a wave that moves out over the surface.  You can make your own interface of two fluids by filling a glass with some water and oil:

A glass containing oil and water.  Oil settles at the top because it is less dense (more buoyant).  [Source: Wikipedia]

Water and oil will separate if left alone.  This separation creates a boundary between the oil and water with the oil on top since it is less dense.  Now imagine gently tapping on the side of the glass.  The vibration from your tap will transfer into the separated oil and water which will produce a gravity wave on their boundary.  If you actually do this carefully enough, you can produce a gravity wave ONLY on the oil/water boundary and not on the surface of the oil (though a surface wave on the oil is technically a gravity wave too since that is a liquid/gas fluid boundary).

While the oil and water example technically illustrates a gravity wave, the term is usually applied to gravity waves that occur in nature.  Examples include:

• The waves on water caused by wind from large ocean waves to ripples in a puddle; these are examples of gravity waves on an gas/liquid boundary.  
• Waves of different density waters under the oceans' surface (like warm/cool water, or fresh/salt water); these are examples of a liquid/liquid boundary.
• The rippling of clouds, like in the movie below; this is an example of a gravity wave on a gas/gas boundary.

CAN A GRAVITATIONAL WAVE DETECTOR DETECT GRAVITY WAVES TOO?

We've now established that a gravity wave is very different from the gravitational waves that LIGO is looking for.  But can LIGO detect them anyway?  Indirectly, yes!  Almost three-quarters of the Earth is covered by oceans.  These oceans are roiling with gravity waves both within the water and on top of it.  When these waves encounter solid earth, much of the wave is reflected but some of the energy is absorbed.  This absorbed energy can then create surface waves on the remaining part of the Earth's surface that is solid.  These ground vibrations are called microseism.

Since LIGO lives on the Earth's surface (many people think that LIGO is underground but it really is built above ground), these vibrations shake the detector and contribute to the measured detector noise.  So much so that, compared to the gravitational waves we seek, we don't expect to be able to detect low frequency (less than about 10 Hz or so) gravitational waves.  And it doesn't matter that both LIGO detectors are near shores since the microseism shakes the entire Earth - we could have built LIGO in the middle of Nebraska and the microseism would still negatively affect us. 

In order to detect low frequency gravitational waves, we need to get away from the microseism.  The proposed gravitational wave detector that can do this is the space-based eLISA satellites.  (I've also discussed eLISA and associated drama on this blog previously.)  eLISA would be exclusively sensitive to low frequency gravitational wave and would compliment LIGO well: there are many young systems producing low frequency gravitational waves all the time while there are few producing the high frequency death throes that LIGO can detect.  Together, LIGO and eLISA will provide a more complete gravitational-wave picture of the life cycle of some of the most energetic, violent objects in the Universe.


CONCLUSION

"Gravitational waves" and "gravity waves" are very different entities.  However, you may hear us refer to a gravitational wave as a "gravity wave".  This is a personal pet peeve of mine (can't you tell?).  While I work hard to use the term "gravitational wave" correctly, I am often hesitant to say anything to colleagues I hear using "gravity wave" instead.  Watch the NSF documentary Einstein's Messengers (also on the "Viewing Fun" page on this blog) and you will see some highly respected LIGO scientists refer to "gravity waves"; it makes me cringe a little every time but I'm not one to gainsay my betters.  Now that you've read this, you'll know what we really mean ;)


Read more:

• Another explanation of the difference between gravitational waves and gravity waves (this is correct but a little outdated on its discussion of gravitational waves)

Happy New Year!

I can't believe how long it's been since I've last blogged - I've had so many ideas of stories to post, but I've also had some life issues that have kept me away.  Not to worry!  My most important resolution for 2013 is to write blog posts a few weeks ahead of time so that I can still post weekly even when life gets in the way.  I will be back in full force in 2013!  Expect posts on Thursdays, unless there is something timely I want to share before then.  I will make sure to post on Twitter when I a new post is available so if you don't follow me already, please follow @livingligo.

This is a smiley face the deicing crew at the Pittsburgh International Airport made in the snow.  As seen through the deicing fluid on the window of my plane on the evening of 29 December 2012.

2012

This year has been a year of many changes for me.  My days as a postdoc have come to an end and I now hold a dual position with Caltech as a scientist at the LIGO Livingston Observatory and as a physics instructor at LSU.  It is great being back in the classroom but that is also something that has kept me from posting as much as I would like.  It takes a lot of time to create interesting lectures for a class of 150 students and handle all of the class administration myself (office hours, grading, etc.).  This semester I am teaching the second semester of physical science (astronomy, chemistry, earth science) and will only have a 30 students.  I am very excited about the more personal instruction I will be able to do!

There have also been many changes at LIGO.  When I first started working at the Livingston observatory in 2007, there were about 25-30 people who worked there on a daily basis.  Starting with the Advanced LIGO preparations in 2010, we nearly doubled the number of daily staff.  Since the installation is well underway, we no longer need to have so many people on site (having too many people on site while we are looking for gravitational waves will cause ground vibrations that will decrease our sensitivity).  The parking lots are noticeably less full and it is starting to feel a little lonely even though we still have more people working on site than when I started.

As far as my personal life is concerned, I'm glad that 2012 is over.  It has been full of drama and uncertainty and it is one of the things that have been getting in the way of keeping up with this blog and my career in general.  But I wouldn't change a moment of it since I have so many great people around me, at home and at work, who care for me. 


2013

This coming year will prove to be exciting!  The installation of Advanced LIGO should be completed and the first commissioning (use of the detector to fine tune it to its best sensitivity) started.  This is always an interesting time when you get to use the detector for the first time and solve novel problems.  I will be sure to tell you all about them here! 

I will also continue teaching at LSU.  As I mentioned above, I will be teaching the second semester of physical science with about 30 students.  I also expect to teach a masters degree class on inquiry learning for in-service teachers this summer (I've done this class twice before with LSU).  

Of course, the most exciting events are usually the unexpected.  I look forward to sharing the professional and personal excitement with you here.

Thank you to all of my readers, followers on Twitter, and those who found me through a search engine!  Keep coming back for more!

What are you looking forward to this year?

Solar Flares and Space Weather

There has been a lot of buzz about the large solar flare that was observed on March 7th (this is one of the strongest flares observed - read about this specific flare here).  Most of the interest in this, other than it is an awesome thing to see, is that the material that was ejected from the Sun can interfere with satellites (like the GPS satellites you need to find your way around unfamiliar locales), power grids, and electromagnetic communications (like radio).  Before I get started, below is a great video of the solar flare using different kinds of light (the Å symbol, called an angstrom, on the left side of some segments of this video is a unit of wavelength equal to 10^-10 meters):

While this is truly an event to behold, there is more to it than just its beauty.  Below is a short video on what you are seeing in this video and how the flare may affect us here on Earth:

The effects of astronomical events interacting with the Earth is called space weather.  (NOAA even studies space weather and you can check the current space weather conditions anytime at NOAA Space Weather Prediction Center.)  If you live north (or south) enough above the Equator (about 70^o or so in latitude) , you may have seen the aurora (known as the aurora borealis [northern lights] if you are north of the Equator or the aurora australis [southern lights] if you are south).  This light display is caused by charged particles from space interacting with the Earth's magnetic field (called the magnetosphere).  This interaction directs the charged particles towards the north and south poles of the Earth.  When the particles strike atoms of our atmosphere, they excite electrons in atoms that make up our air; light is produced when these excited electrons release this excess energy.  Since our atmosphere is made up primarily of nitrogen and oxygen, the colors of this light are usually red (from nitrogen) or green (from oxygen).  This recent solar flare is starting to interact with the Earth now and brilliant aurorae are expected.  Since I am posting videos today, below is a spectacular time lapse video of the aurora borealis by National Geographic (there may be a short advertisement before it starts - sorry!):

I bring all of this up, not only because it is timely and interesting, but also because space weather affects LIGO.  Space weather often produces particles that shower down on the Earth's surface called cosmic rays (even though most of the particles are not from space but are produced when very high energy particles from space smash into the atmosphere and produce showers of new particles from this interaction).  Of particular concern to us is what would happen if a shower of particles are produced near or within one of our mirrors.  Could this cause a vibration big enough for the detector to be sensitive to?  If so, could the motion look like a gravitational wave signal?  A paper published in 2008 investigated this (which you can read here if you are REALLY interested).  It was determined that a strong shower could indeed move our mirrors enough for us to notice, but a strong shower like this is rare.

Even though the effect is rare, so is detecting a gravitational wave (at least until Advanced LIGO is completed).  For the "Big Dog" event - when we last thought that we may have really detected a gravitational wave but it was later shown to be a blind test of our detection methods - the possibility that space weather could have affected our results was thoroughly investigated (along with many other things like one of us turning to the dark side and fraudulently adding this signal to the detector).  As it turned out, it was a "clear" space weather day for that event.

Remember to check the NOAA Space Weather Prediction Center for updates on the effects of this recent solar flare here on Earth!

On Leap Years and Keeping Time

I hope everyone had a good leap day (I know it isn't a holiday, but it is even rarer since it only comes about every four years).  In honor of this, I am discussing why we have leap days and different calendar systems.  I'm not sure what you think, but while I find all of this fascinating, I'm happy this isn't something I study for a living!


There are many different calendar systems that base themselves on the periodicity of different things - most of them having an astronomical origin like the Sun, Moon, or even Venus.  The system in most use today is the Gregorian calendar (at least for international commerce in countries that use a different system).  This is a solar calendar that assigns a date to every cycle of day and night.  This has the advantage of syncing up well with the normal human sleep cycle.  However, the Earth does not revolve around the Sun in an integer number of days.  While our normal year has 365 days in it, it actually takes the Earth 365.242374 days (and the length of a day is slowly increasing) to orbit the Sun.

If we did not correct for that extra fraction of a day, the seasons would slowly start changing later and later on the calendar.  Over an average human lifespan, say 75 years, the equinoxes and solstices (start of seasons) will be a little more than 18 days later at the end of that 75 years than at birth.  This year, the summer solstice is on June 20.  If we never have another leap day, summer will start on Christmas (December 25 is 188 days after June 20) in 776 years.  I know you and I wouldn't be around to see that, but on the human history scale of things this is very significant.

But our leap year every year that is evenly divisible by 4 system is overcompensating for that extra fraction of a day it takes Earth to orbit the Sun.  So exceptions to the every 4-years rule must be made: every year divisible by 100 is NOT a leap year EXCEPT if it is divisible by 400.  That is why 2000, even though it was divisible by 100, was not a leap year since it was also divisible by 400.

The reason I am going into this on this blog about LIGO is that keeping time is VERY important to us.  It is also important to astronomers in general.  There have been many revisions and changes to the calendar over the years (before the Gregorian calendar, most of Europe used the Julian calendar) and this can complicate figuring out how long it has been since something happened.  So that we don't have to worry about these complications, astronomers use the Julian date system (which is different from figuring out the date on the Julian calendar mentioned above).  This system assigns a date to every day consecutively (there are no months or years).  For example, today is 2455988 (any fractional parts would  correspond to the time of day).  Day 0 is assigned to be January 1, 4713 BC (this is roughly around the beginning of human recorded history).  This makes it is very easy to figure out how many days there have been between events; for example, I was born on 2443787 so I am 12,201 days old (today).  Here at LIGO, we use a system called GPS time which counts the number of seconds since January 6, 1980 (I wrote a post about this here).  In GPS time, I was born on -39489840...  Now I feel prehistoric!

Remember in the first paragraph when I mentioned the day is getting longer?  One of the predictable reasons for this is the effect of the tides on the Earth cause it to rotate a little slower over time (this is called tidal breaking).  Other factors that are not as predictable can also effect the length of a day, like the motion of the molten mass inside the Earth.  A 2004 earthquake was so powerful that the length of the day became 2.68 microseconds shorter.  There are also unpredictable reasons we don't understand that cause the length of the day to change (in 1999 it changed by about 1 microsecond and we don't know why).  But, factors like this cause there to be such a thing as a leap second (there will be a leap second on June 30 this year).  Date systems like Julian dates and GPS time are not affected by this unless you want to convert back into normal dates and times - here at LIGO we make sure that all of our computer programs keep up to date with the leap second corrections.

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Yesterday (leap day) I was leaving work by way of a staircase in the back of my building.  This faces the woods and there is a single light above them so you can see your way at night.  This is a prime place to find the varied kinds of moths that are indigenous to the area because many of them are attracted to the light and some die during the night.  I guess I got a leap day treat yesterday when I saw this moth I have NEVER seen before with beautiful pink and yellow colorings:

I looked this up later and discovered that this is a rosy maple moth.