A few weeks ago, when the first news on the Higgs boson came out, a friend of mine sent me an email requesting that I write a blog entry explaining what it’s all about (that blog entry will be coming next week on Laser Mom). He said that understanding this part of physics was hard for him as an engineer since he did not have much background in modern physics. He also asked,  “Why do we care about what gives us our mass?”

His question made me think about research in general. Of course, as scientists and engineers, we all write proposals to get funding, and papers for scientific journals, and give conference talks, and spend quite a bit of time explaining why what we do is useful and will save the world and make us all rich someday. But really, why do we really do our research? I think that most us can honestly say (hopefully!) that we do it because it’s really cool. It’s fun. Why do we want to find out what gives us our mass? Because we can. We are curious and want to understand how things work and what new things we can accomplish.

One of the things that I have done in the recent past for research is to shine laser beams into glass or polymers (i.e. plastic) and see what happens. It turns out you can use the energy in the laser beam to change the properties of the materials for practical engineering reasons – creating small feature sizes so that we can have better, faster, smaller computers and to write optical waveguides so that we can send information (internet) easier and faster from place to place. But I did not really study this just for practical reasons – it’s just fun! (The practical reasons are, of course, important to get funding to get paid to do what I love.)

I have to wonder if the first scientists to write optical wires in glass with high power lasers were not thinking (at least a little bit), “This laser is so cool. I wonder what would happen if we focused it down into that piece of glass? Will the glass vaporize? Let’s try it!” (I believe Davis et al. were the first to publish on this topic.)

Perhaps they were much more organized and focused in their pursuits, but I have to admit that most of the interesting things I have accomplished in the lab have started out with, “I wonder what would happen if…”

My one year old daughter is a natural experimentalist. She loves to try out new things and do things just to see what happens. If I drop this, what will happen? What if I pull on this handle? What will happen if I pull myself off of this landing (Ow!)? It is amazing to see how quickly she learns new things just by exploring and trying everything that comes to mind.

We have all (hopefully) mastered the basics of gravity at this point, but our curiosity and desire to try out new things is what makes us good scientists. Shining a laser beam into a light sensitive polymer and watching what happens just fascinates me. There are so many interesting things going on, from basic light propagation in glass/plastic to chemical reactions in the material.

Then there are a the cool things you do when you put two laser beams together – using different colored laser beams of different shapes to activate different chemicals in a material and making super tiny little dots in the material. There were three papers in Science a few years ago (May 15 2009 issue) discussing different ways of combining optics and chemistry to create features that were smaller than anything you could do before with these lasers (By the way, you can get all three of those papers for free if you sign up on the Science website.)

Oh sure, there are lots of good practical applications of shining lasers into materials (faster internet and computers?) and those are probably the things I will tell you if you ask me to give a talk on this research and certainly what I will tell you if I need to write a grant proposal.

But why do I really work with lasers, shine them into materials, use them for microscopy? Why are the scientists at CERN looking for the Higgs Boson?

I think the Mars rover’s name covers it: Curiosity.  Anyone who watched the video of Curiosity’s landing (YouTube – watch between minutes 5 and 6) can see the excitement and joy that scientists and engineers get when they have successfully completed a mission, discovered a new particle, built a new gadget or made measurements that no one before them has ever been able to do.

As scientists and engineers, we are a curious folk. Sometimes we get so wrapped up in funding, papers, etc. that we forget why we do what we do. That’s one of the reasons I am excited to go to an optics conference this fall. Conferences are a great opportunity to explore and enjoy that curiosity. We can go to talks outside our field, talk to other scientists we have never met, and get outside our normal routine. This setting always re-energizes me and gives me lots of new ideas of things I would like to explore when I get back to the lab.

Of course, with an infant at home, I do not really need to go anywhere. Babies are natural experimentalists and seeing her intense concentration in trying something new and her joy at discovering new things reminds me every day why science is so cool. We are all born curious, and hopefully we keep that curiosity as we grow older though we each tend to focus it in different directions.

Seasons (or Why My Front Door is Hotter in Winter than Summer)

We moved to CO a few months ago and when we first moved into our new place, I noticed that our front door, which is south facing, became very hot on sunny days. This was March and so I was worried what it was going to be like in summer. Even in March, I was afraid my daughter was going to hurt her hands is she touched it. Interestingly, now it is June, and it is regularly 90 deg and sunny, but the front door stays cool to the touch. This got me thinking about the sun and seasons…

If you have not taken an Astronomy course, you may not spend a lot of time thinking about the solar system and how the Earth moves in relation to the Sun. You may also not have thought much about what causes summer and winter and why the days are longer in the summer.

This week is the summer solstice for the northern hemisphere. The solstice this year is June 20. So what is the solstice, what does it mean about the Earth and the Sun and why do we have seasons? Why does the Southern Hemisphere have opposite seasons?

A common misconception is that summer occurs when the Earth is closest to the Sun and winter occurs when the Earth is farthest from the Sun. Let’s think about that a little more. I found this chart in Lecture-Tutorials for Introductory Astronomy by Edward Prather et al.:


Earth-Sun Distance


147.2 million kilometers


152.0 million kilometers


150.2 million kilometers


149.0 million kilometers

There are a couple of things I can learn from this. First, the Earth is not always the same distance from the Sun. Second: It is June now and we seem to be at our farthest point from the Sun. Wait a second! It’s hot now. It’s summer, right? Shouldn’t we be closest to the Sun?

The Southern Hemisphere has winter in June when the Sun is at its farthest point, but the Northern Hemisphere is enjoying summer in June. If the seasons were caused by our distance from the sun, both hemispheres would have to experience summer (and winter) at the same time. But we have opposite seasons, so the distance from the Sun can not be what causes our changing seasons. Well, then, what does?

We know that the Earth is warmed by radiation from the Sun – sunlight. The Earth is also tilted with respect to the Sun at about 23.5°, so that it looks like this as it orbits:

Sometimes the northern hemisphere is tilted toward the sun and sometimes it is tilted away from the sun. When the north is tilted toward the sun, we get more direct sunlight hitting us. The Sun appears to be higher in the sky in the summer when we are tilted toward the sun. Direct sunlight gives us more heat. Think about going for a walk in the summertime. Does the sun feel hotter in the middle of the day when it is directly above or in the early evening when it is low in the sky? The sun definitely feels most intense to me in the middle of the day. I tend to go on walks with my daughter in the morning and the evening.

This more direct sunlight gives us more heat and causes the change in seasons that we experience.

At the north pole, this tilt is enough that in the summer, there is always sunlight hitting the ground and there is no night at the peak of summer. The farther north you are (or south in the southern hemisphere), the more dramatic the change in light and temperature is. Near the equator, there is always plenty of direct sunlight regardless of the season and so the temperature remains warm year round. However, far from the equator, the amount of sunlight hitting the ground changes dramatically due to the tilt of the Earth and so the temperature also changes quite a bit from season to season.

The summer solstice on June 20 is the time when the tilt of the Earth and the rotation around the Sun causes the northern hemisphere to get the most direct sunlight. The sun is highest in the sky in the north and daylight lasts longer than any other day of the year.

So what does this all have to do with my front door? In the spring and winter, the sun is low in the sky to the south and so my front door gets a lot of direct sunlight. However, now that it is summer, the sun is high in the sky and the eaves on the house block the sun from hitting the door. Here is my silly exaggerated picture of this:

Phew! So I do not have to worry about my daughter burning her hand on the door. Of course, it is hotter outside and the sunlight is generally more intense, so I have to worry about other things like sun hats, sunscreen, sun shades on the car, etc. She is very fair of skin (like her mother) and will likely burn easily with the intense summer sun.

Venus Transit

A couple of weeks ago, I wrote about the solar eclipse that was visible in the Western US. Unfortunately, the weather did not cooperate with my eclipse viewing. I think if I had really tried to see it, I would have been able to see something through the clouds, but there was also a tired and fussy baby involved in the equation.

For those of you who also missed it, a few of my friends posted some pictures of the eclipse on Facebook and gave me permission to share them here:

Partial eclipse in Chicago, IL. (Ivy Fitzgerald)

Annular eclipse through eclipse viewing glasses (left) and through the clouds (right) in Tokyo, Japan. (Amy Lovell)

Or if you’d like to see a time lapse of the entire eclipse, here is one of many YouTube videos.

While I missed the eclipse, there is another exciting solar event coming up: the Venus transit. This is very much like the solar eclipse, only this time, Venus will be blocking the sun instead of the moon. Of course, Venus appears much smaller than the moon to us on Earth, so instead of blocking the entire sun, Venus will just appear as a black dot moving across the sun.

Why does Venus appear so much smaller even though it is actually much larger than the moon? The apparent size of objects in the sky depends on the ratio of the object’s size to the object’s distance from us.

For example, the sun and moon appear to be about the same size in the sky from our viewpoint on Earth. This is why we can have a total solar eclipse where the moon completely covers the Earth. Looking on Wikipedia for estimates of sizes and distances, I find that:

This ratio is almost the same using some average, approximate values for distances. This is why the sun and moon appear to be the same size in the sky when we look up.

So how big will Venus be compared to the sun (or moon)? The Earth orbits the sun at a distance of ~150 million km, while Venus orbits at a distance of ~108 million km. So, when Venus is directly between the Earth and Sun (when we see this Venus transit), it must be ~32 million km away. Venus is approximately the same size as the Earth and so

So Venus will appear much smaller than the Sun. These numbers do not give me a good idea of what this will look like, but this picture from the Wikimedia Commons might help:

This is a fairly small dot, but definitely visible and I am excited about the chance to see it!

We have all probably been told from a young age that we should not look directly at the sun, so how are we supposed to view this transit? The sun is so bright it will actually damage our eyes. There are several different types of methods of looking at the Venus transit (or a solar eclipse) safely. A number of online stores sell “eclipse viewing glasses” which are really just filters that block the sun. The standard set of glasses appears to be made of Optical Density 5 filters. This means that the light that passes through the glasses is 105 (or 100,000) times less than the light that enters the glasses. You can still see the sun through the glasses, but it appears 100,000 times dimmer so it will not damage your eyes. Another good method is to use binoculars, or a telescope or other lens to project an image onto a piece of paper other surface. Do not look at the sun through the lens!!! This would certainly cause you harm! But, if you point the binoculars at the sun and put a surface behind the viewing lens, you will see an image of the sun that you can look at.

The Venus transit will be visible over much of the world, including all of the United States. NASA has a map of visibility if you would like to know if you will be able to see it and when. Click on Local Transit times in the bottom right to find out when you can see the transit at your location. We should be able to see it in the late afternoon/evening of June 5. I am hoping the weather cooperates this time so that we can go out and look! I even got some eclipse viewing glasses for the occasion.

This will not happen again in our lifetimes, so you should try to go out and see it. If you live in a part of the world where the transit is not visible, or the weather does not cooperate, NASA is also broadcasting the transit live from Hawaii so you can watch it on your computers at home.

UPDATE after the Venus Transit:

We were much luckier this past week in our solar viewing. The afternoon was partly cloudy again, but the Venus Transit started around 4 PM and lasted through sunset where we live, so there was a much bigger window during which we could try to find a sunny moment.

As mentioned last week, Venus looks much smaller than the Sun as viewed from Earth and so it was difficult to see the Venus transit just using eclipse glasses and our eyes. We may have been able to project an image using binnoculars or our little telescope, but do not have a fancy telescope and as always, have a little girl who had little patience with this watching the sky nonsense. However, we were able to see the Venus transit using our digital camera with the eclipse glasses in front of the lens. Here are some pictures my husband took:

These both show the image of the sun through the glasses, which filters out most of the light. The black dot is Venus moving between the Earth and sun. The image on the left was taken at 5:58 PM and the image on the right was taken at 7:12 PM. You can see on the right that the clouds have come in, partially blocking the light from the sun.

It was exciting to get a chance to see the transit since it won’t happen again until 2117. If my daughter lives for a very long time, she may get to see the next one, but I am certainly going to miss it!

Solar eclipse

There is going to be a solar eclipse visible in the Western United states this evening (and in east Asia, but I live in the US). This will be the first solar eclipse for my daughter, so hopefully the weather cooperates and we can go out and see it. Of course, she probably won’t even notice it and I should not encourage her to look at the sun anyway.

What is a solar eclipse and what causes it?

We know that the Earth orbits the sun and the moon orbits the Earth. Sometimes these orbits are lined up so that the moon passes between the Earth and the sun, blocking the light of the sun from reaching us. This causes a solar eclipse.  Below is a picture from Wikipedia Commons illustrating this effect.

 The umbra is the area on the Earth where the light from the sun is completely blocked. This is a total eclipse. The penumbra is the area where the light from the sun is only partially blocked. Outside these areas, an eclipse will not be viewed – the moon will not block the light from the sun at all. 

The eclipse this weekend is going to be annular eclipse for some areas. This is what you see when the moon passes directly in front of the sun, but is not large enough to block the entire sun. Some light makes it past the edges of the moon and is seen on Earth.

Below are some rough drawings of what the different types of eclipses look like:

The type of eclipse depends on the exact path of the moon and where on Earth you are viewing the eclipse.

Why does the moon sometimes block all of the light from the sun and sometimes only some of the light? The amount of light blocked depends on the moon’s distance from the Earth. When the moon is closer to the Earth, it casts a bigger shadow, and when it is far from the Earth, it casts a smaller shadow. To understand this, close one eye and hold your thumb up in front of the other eye. Now look at something far away.  If you hold your thumb close to your eye, it likely blocks the entire object you are looking at. However, if you move your thumb as far away from your eye as you can, it blocks a much smaller area of the object.

The moon does not orbit the Earth in a perfect circle. The orbit is an ellipse (oval shaped). That means that sometimes the moon is close to the Earth and sometimes it is farther away.  The closest point is called the perigee of the orbit and the farthest point is the apogee of the orbit. When there is a full moon at the perigee (or close to it), it is sometimes called a ‘supermoon’ because the moon seems very large and bright. This happened earlier this month, on May 5 (the perigee was on May 6). A calendar of apogee and perigee dates can be found here.

Eclipses only occur during a new moon. The new moon is when the moon is dark – the opposite of the full moon. A full moon occurs when the the light side of the moon is facing the Earth. This is caused by the light of the sun reflecting off of the moon and hitting the Earth where we see it since the moon does not emit visible light on its own. If the moon is blocking the sun, as during an eclipse, the light side must be facing the sun (and the light reflects away from us)and the dark side must be facing the Earth.

Today, there is a new moon close to the lunar apogee (May 19), so the moon will be almost as far away as it gets. Therefore, the shadow it casts will not completely block out the sun, allowing for some people on Earth to see an annular eclipse.

Will I get to see the eclipse?

Solar eclipses are fairly common on Earth, but each eclipse can only be seen by a relatively small area of the Earth. Therefore, eclipses at a particular location are not that common. If you live in the Western US, there will be an annular eclipse today, May 20, 2012. Much of the Western US will only see a partial eclipse. If you would like to find out what time the eclipse will occur at your location, or when the next solar eclipse will be, check out NASA’s Solar Eclipse page.  This page requires you to either pick the city closest to you, or enter the exact coordinates of your location. If you would like to enter your coordinates, you can find most towns and cities on Wikipedia, with the coordinates listed on the right hand side of the page. Or you can use Google Earth to find the exact coordinates of your house. NASA also has a special page with information on today’s solar eclipse.

We will not be in the area where the annular solar eclipse will be visible, but I am excited about being able to see the partial solar eclipse tonight.

Peer Reviewed Journal Articles

I usually work on my blog entries on Saturday mornings at a coffee shop so I can get away for a few hours and concentrate. I find it difficult to make much coherent progress on anything Physics related in the short periods of time I get during the day while my daughter naps (especially when she takes short naps like she has lately). At home, I am distracted by all the household work that needs to be done – bills to pay, laundry, dishes, and lately, unpacking.

This Saturday, however, I found myself having to do some other Physics related work. I find it interesting that despite the fact that I am not currently gainfully employed and have no official affiliation to any teaching or research institute, that I still have research work to do. I was asked to review a journal article for Optics Express, an open-access online journal published by the Optical Society of America. Doing a good review of a journal article takes a good amount of time and so I spent my Saturday morning working exclusively on this task.

So, instead of a blog entry on teaching or the Physics of babies, I thought you all might be interested in learning more about the peer review process – how are journal articles reviewed and published? I think this is particularly interesting in the world of constant information online from all sorts of reliable and unreliable sources. When teaching, I tried to help my students understand the importance of using peer-reviewed sources. While the system is certainly not perfect, these sources from good journals are much more reliable than news articles and other online sources written by non-experts.

Why do scientists bother to write these journal articles? Researchers are required to publish to show that they are doing ‘worthwhile’ research. It is generally a requirement to graduate with a PhD, get a research position, and get promoted. This applies mostly to academic institutions as private companies tend to want to keep their research private.

So how does this work? You do some research and get some cool results – you either build a new widget that you think has potential to change the world or measure something better than everyone else. Or, usually, something less impressive but still interesting. I have a couple of published journal papers on shining a laser beam into a photopolymer (plastic that is sensitive to light) and making the plastic change in interesting ways. Fun stuff.

Then you describe what you have done in enough detail that a reader could replicate your work. That is the goal at least, but with time and page limits, we all tend to leave out important details. You format the paper to the right page length, font, etc. for a specific journal and you send it to them and say, “I would like you to publish this in your super awesome journal.”

Next the editor looks at the paper and decides whether or not to even review it. If you send it to a very prestigious journal (Science and Nature are two), it may be rejected out of hand if it is not considered new and interesting enough.

If the editor decides the paper has some merit, s/he sends the paper to a set of reviewers, usually three different people. These reviewers are scientists who have published in that journal in the past and do work that is related to the content of the paper. I was reviewing a paper this past week for Optics Express because I have two past publications in that journal and the topic of the paper was related to photopolymers, which I have done research on in the past.

So I get this request to review the paper. Here comes one of the ‘not such a good system’ parts of the review process. The peer review process is constantly criticized for taking too long to review and publish new research. The online publications try to work faster. So I was given one week to review a paper. This is not a long time when you are home with a baby and do not have a lot of free time. It takes several hours for me to critically review a paper, and longer depending on the complexity and quality of the paper. This short turn around time can definitely result in a poor paper review.

But I agreed to do it and I did.  Reviewers are asked to consider the following questions (these are specifically for Optics Express but are similar for other journals):

  • Does the technical content merit publication in this journal?
  • Is this paper an original and significant contribution?
  • If it is not original, can you cite prior publications on the subject?
  • Are the results significant to the field and/or offer interdisciplinary application?
  • Are conclusions supported by the data presented?
  • Is the work placed in proper context?
  • Is related work adequately referenced?
  • Does work warrant publication in an archival journal?

There are several options for a review:

  1. Accept the paper with no changes. It’s awesome. Publish it as is. This is not common. I have never done this, but did have one paper that received this review. You sort of wonder if they read it when this is the response you get.
  2. Accept the paper with revisions. This comes in two forms:
    1. Minor revisions: I make suggestions for changes but consider them minor enough that I do not need to re-edit the paper. The journal editor is in charge of making sure those edits are made.
    2. Major revisions: I list things that need to be changed to make the paper publishable and request to re-edit before the paper is published.
  3. Reject outright. I have only done this twice. Once for a paper that was in such poorly written English that it was unreadable. And once for a paper whose authors ignored the reviewers comments (despite all three reviewers making the same comments).

Some examples of changes that might need to be done:

  • Clarify a point that is not clear.
  • Add or improve a figure or picture that is not clear.
  • Fix a mistake in an equation or calculation.
  • Describe in more detail why your research is interesting or relevant and why people might want to read your paper.
  • Add data when it does not seem that you have sufficient scientific data to back up your point.

Really, anything at all that would make the paper a better paper can be suggested. The idea is to hold the authors to a high standard of scientific research – you expect that their work is careful, well thought out and honest.

The editor takes the reviewers comments and sends them on to the author or edits them. If the reviews are wildly different, s/he might get another reviewer.

The reviewers do not get paid. I do not get anything at all except the right to put this on my resume as “service to my field of research.” It is expected that scientists take the time to review papers as carefully and thoughtfully as they would like their own work reviewed. The system is not perfect, but having at least three expert reviewers and an editor keeps things honest.

This is very different from the review process for most information online and I consider these journal articles to be a much more reliable source of information. Of course, most are so technical that only an expert in the field would understand them, so that’s not too useful. Like I said: The system is far from perfect.

Airport body scanners

I have been in the middle of a cross-country move the past few weeks, which has been quite challenging with a baby in tow. According to Google Maps, we moved 1423 miles from our old home to our new home. We also moved 4292 ft higher in elevation (according to Wikipedia). No wonder I am exhausted

For work reasons, we needed to move rather quickly. Normally, we would have driven, which takes about 24 hours. With stops for feeding, changing, and soothing a baby, that would have been at least 3 long days, or 4 or 5 if we took our time and stopped to see things on the way – after all, if you are going to drive more than 1400 miles, you might as well see the sights along the way. Unfortunately, we did not have time for that this trip, and so I flew with my daughter to our new home.

I am a relatively frequent flyer and adept at getting through security quickly and efficiently, though it is definitely more of a challenge now that I have a baby with me. I, like all of you who fly I’m sure, have noticed the increasing number of airport body scanners in the security line over the past couple of years. My first experience with one was returning to the US from an international flight in the spring of 2010. Now they seem to be in all the airports that I frequently fly through.

There are a number of issues surrounding these scanners: privacy, effectiveness, cost, and safety. There are huge numbers of articles around the web on each of these issues. I started to think seriously about the last one – safety – last year when I was pregnant. I went on three plane trips while pregnant and was wondering if the scanners were safe for my unborn baby. I never had to walk through one of these scanners during those trips, and so I did not give it much more thought. Then I started traveling with my daughter and wondered once again whether or not these scanners are safe for her. It is interesting that it never occurred to me to worry about this for my own safety, but I guess we are always more concerned about keeping our children safe.

Ignoring all the other issues (which may also be very important to you), let’s take a look at how these scanners work and whether or not they are safe for us to walk through.

There are two types of scanners that are currently in use in the United States: millimeter wave three dimensional scanners, and x-ray backscatter (two dimensional) scanners. They use different wavelengths of light (both invisible to the eye) and different methods of making an image.

A few weeks ago, I had a blog entry on how CT scans work. These body scanners are very similar in a lot of ways, so let’s review a few of those ideas, starting with wavelength. The electromagnetic spectrum (the different wavelengths and frequencies of light) is shown below:

I did not mention the relationship between wavelength () and frequency (f) in my previous blog entry, but here it is:


where c is the speed of light, 3 x 108 meters/second (or 186 miles/second). This is true for all wavelengths of light traveling through air. Who cares, you say? Well, this means that the millimeter wave beams have a frequency of ~ 300 GHz and below. For reference, your cell phone uses waves that have a frequency of ~ 1 GHz. The x-ray beams have frequencies of greater than a million GHz, or about 10,000 times that of the millimeter beam waves.

Again…this is interesting and all (if you are into numbers), but why should I care? Well, the energy contained in the individual balls of light (photons) in these beams is directly proportional to the frequency of light. That means that the x-ray photons hitting your body have more than 10,000x more energy than the millimeter wave photons. These high energy photons can actually ionize atoms – that means they can remove electrons from the atoms in your body, which can change the ways your atoms chemically bond and form all the organic material your body needs to function correctly.

So that is why x-rays are more dangerous than millimeter waves (which have not been shown to have any lasting harm on your body as far as I know). The question of safety seems to lie in the dosage. The backscatter scanners only send a very small amount of x-rays at your body.

According to the Transportation Security Administration (TSA):

“Advanced imaging technology is safe and meets national health and safety standards. Backscatter technology was evaluated by the Food and Drug Administration’s (FDA) Center for Devices and Radiological Health (CDRH), the National Institute for Standards and Technology (NIST), and the Johns Hopkins University Applied Physics Laboratory (APL). For comparison, a single scan using backscatter technology produces exposure equivalent to two minutes of flying on an airplane, and the energy projected by millimeter wave technology is thousands of times less than a cell phone transmission. Millimeter wave imaging technology meets all known national and international health and safety standards. In fact, the energy emitted by millimeter wave technology is 1000 times less than the international limits and guidelines.”

So this sounds like the scanners are safe, right? But the European Union has banned the x-ray backscatter scanners. From a European Commission Press Release:

“In order not to risk jeopardising citizens’ health and safety, only security scanners which do not use X-ray technology are added to the list of authorised methods for passenger screening at EU airports.”

Why? Well, the backscatter machines concentrate the x-rays on our skin. Unlike for CT scans, the x-rays do not travel through our bodies, but are reflected backwards to a detector to form an image. Some scientists, like the ones from the University of California at San Francisco that wrote a Letter of Concern printed in this news article, are concerned that the scanners have not be accurately tested and evaluated for this use. They believe that until these tests are done, the scanners should not be used in airports.

Okay, so we have heard this all before. They are safe. They are not safe. What does this mean? I feel that there are enough intelligent people (scientists, officials in Europe) who do not feel the machines are safe, especially for children. I will not walk through one of the x-ray backscatter machines with my daughter. (Of course, it is unlikely I will ever have to since I currently have to carry my daughter and that would defeat the purpose of the scanners – I could just hold her in front of my body wherever I was carrying something forbidden on airplanes.)

I do believe that the millimeter scanners are safe and have no problem walking through those. My next question was this: How can I tell which is which? It turns out they look completely different. There are number of pictures online showing what they look like. This article on The Science Behind Airport Body Scanners shows the scanners side by side so you can see what they look like.

Now I can make an educated decision about whether or not to walk through the scanner I see in the airport. I have only seen the millimeter wave machines and am not sure what airports have the x-ray backscatter scanners. If anyone has found a list of what airports carry which scanners, please leave a comment – I would be interested in knowing.

Side note: We are still in the midst of settling in and so the blog entries will likely be shorter and/or later than usual for a few weeks until I can find the time to work on them.