Curiosity



Did curiosity really kill the cat? If life on Earth originated on Mars, then who knows? Maybe we landed on one. At 1:32 AM EST on August 6th, millions of people breathed a sigh of relief and became giddy school girls in their computer chairs. The 900kg Mars Science Laboratory (more affectionately known as the Curiosity rover) touched down on Mars.

The MSL touchdown is one of the greatest accomplishments of humankind to date. We sent a car sized vehicle ~51000000km into the inky black darkness to land on a reddish pinpoint of light. With speeds of up to 13000km/hr, this journey took 8 months to complete. Unfortunately for Curiosity, no matter how much we asked “Are we there yet”, it wasn’t allowed to get angry and turn the ship around. Before Curiosity even reached Mars, it was recording invaluable information about the radiation levels [1] a manned mission to Mars would experience. How cool is that, really? Radiation is one of the most dangerous parts of space travel, and we now know what to be expecting so we can keep future pioneers safe.

Upon reaching Mars, at approximately 1:00 AM, everyone that had interest in Mars exploration was on the verge of soiling themselves due to the 7 minutes of terror. This was the amount of time it took for Curiosity to go from Mars’ upper atmosphere to landing safely on the ground. It was travelling 13,000km/hr upon hitting the atmosphere, which required a heat shield to prevent the rover from turning into a carbon scored hunk of scrap metal. This slowed everything down to about 1400km/hr, at which point the heat shield was ejected and a massive parachute was deployed. Now although there is enough atmosphere to destroy Curiosity without a heat shield, there isn’t enough to actually slow it down to a reasonable speed with a parachute. Once the speed slowed down to 200km/hr, the parachute was detached and the skycrane was ejected. The skycrane has a lot of rockets on it which further slowed down the rover to landing speed, and then hovered about 20m above the ground and slowly lowered the actual Curiosity rover to the surface with several cables. So there was a lot of opportunity for everything to go terribly wrong, and it was like a science fiction landing. The most terrifying part for those involved though is the fact that light takes roughly 14 minutes to get to Earth from Mars. If you recall from my previous post, any information that is transmitted across the universe does so in one form of light or another. So this means while us Earthlings were watching on the edge of our seats as the seven minutes began, Curiosity had in reality already either landed or crashed onto the surface of Mars and been there for 7 minutes. In the end though it was a beautifully successful mission, and a lot of tears of joy were shed in the control room.

Now you may be asking me why that alone is such a revolutionary accomplishment. After all, we already have some rovers on the surface of Mars. Well stop, because you look like a fool talking to your computer like that. I can’t actually hear what you’re saying. But to answer your question, that isn’t the revolutionary part. The landing was just really freaking impressive and amazing. The MSL itself is what is so revolutionary. It isn’t just a rover. Like its name suggests, the MSL is a fully functioning scientific laboratory. Since we can’t bring samples of Mars back to Earth to analyze, we sent the equipment there. We’ll be able to look at Mars in a way that we’ve only dreamed of in the past.

The first section of equipment that will be the most interesting to us back home is the cameras. There are (kind of) three cameras on Curiosity. The first is MARDI, or Mars Descent Imager. This took high resolution images on the way down to the surface at a rate of four frames per second. This will help determine the precise location of the lander, surrounding topography, and descent information. It’s all useful and cool, but nothing too spectacular on your own. The next camera on board is MAHLI, or the Mars Hand Lens Imager. If you’re familiar with geology, you know that a hand lens lets you look at samples of earth and rock with a surprising level of detail. MAHLI goes beyond that, and looks at samples of mars and rock down to a microbial level. It can look at details at a level of 12µm, which is smaller than the width of a human hair. This is the camera that will be looking for signs that Mars was once habitable by analyzing the geographical history. Geology rocks! (Sorry). As amazing as MAHLI really is, the last camera is the one that I’m looking forward to the most. It is the Mastcam. Mastcam is the camera that will be sending us the most beautiful pictures of Mars we’ve ever seen. It is a High Definition camera that can take 10 frames per second, which can be put together to form what is essentially a stop motion video. It has two lenses that can create stereoscopic images. One of the lenses does operate at a lower resolution to get general images, while the higher res camera will take a detailed look at terrain features. This camera also has an internal storage of 8gb so that it can compress some images before sending while keeping others at a full HD resolution.

MSL also has four spectrometers on board, which to me are the heart of the mission. In case you aren’t sure what a spectrometer does, here’s a quick rundown. It shines a beam of light, and analyzes the wavelength that gets reflected/refracted around. Since different elements and particles interact with light differently (which is why leaves are green, the sky is blue, and your bones show up on x rays), you can look at the way light reacts and determine the chemical makeup of whatever you’re analyzing.

The first spectrometer is APXS, or the Alpha Particle X Ray Spectrometer. This spectrometer was made in Canada, which I personally take great pride in. As the name implies, this will expose samples of soil and rock to Alpha Particles and X rays. This will expose all the rock forming elements to us, which will allow scientists to determine how the rocks formed, and if they’ve been eroded by wind, water, snow, or other elements. The next spectrometer is unbelievably amazing. It’s the ChemCam. From 7m away, this will be able to fire a laser (That’s right, like a little Death Star) at rocks, vaporizing a small area of them. It will then use its camera to analyze the plasma that’s floating around it. From that range it will be able to determine the origin of the rock, analyze chemical elements located in the soil/rocks, and identify ice and water trapped within rocks. CheMin is the next spectrometer, or the Chemistry and Mineralogy instrument. This will take samples and fire a hair-thin beam of x rays at them to measure the abundances of different kinds of minerals. From the amounts and types of minerals discovered, we will be able to determine how and when they formed. Some form from lava flows, some will form from water or air exposure, and some will form from extreme pressures. There’s many more combinations and sources of minerals, but this will give us a historical map of what happened geologically in a given area. Next up is the Sample Analysis at Mars, or SAM (Quite different from the SAMs that are on rooftops in London). This is the bulk of the scientific research on board the MSL, taking up half the science payload. This is the piece of equipment that will be able to tell us if Mars at any point has been hospitable to life. It has a Mass Spectrometer, Gas Chromatograph, and a tunable Laser Spectrometer. These tools combined will be able to look at carbon compounds that are associated with life, the ways these compounds may have been formed (through natural events or biologically), and look at several lighter elements that are frequently associated with life such as hydrogen, nitrogen and oxygen. With all the spectrometers on board, we’ll have a comprehensive look at what was going on over the past billions of years in any given location on Mars. We’ll see how the land formed, whether the area was volcanic, how much water may have existed, how the ground may have changed over the years, and whether or not there are past traces of life that could match the identified environments.

There are two radiation detectors on board Curiosity. One is named DAN, or Dynamic Albedo of Neutrons. This was placed on board by the request of the Russian government. It will launch a beam of neutrons towards the ground, which will penetrate the surface. If these neutrons encounter hydrogen (indicating water), they will reflect back up to the sensor more slowly than they would otherwise. This is sensitive enough to detect underground water in traces as small as 1/10th of 1%. The second rad detector on Curiosity is the RAD, or the Radiation Assessment Detector. This is meant to detect high energy levels of radiation that could be harmful to life on Mars. It will be able to analyze the equivalent dosage of radiation hitting the surface, which is a measure of lethality to humans. It will also look at the effects of radiation on potential microbial martian life, past and present. This detectors main purpose is to look at the survivability of a manned mission to Mars.

There is also an environmental and atmospheric sensor on board. The Rover Environmental Monitoring Station or REMS, was provided by the Spanish government. It was a weather station that will be able to monitor wind speeds and directions, surface temperatures, ultraviolet radiation exposure on the surface, air pressure, and humidity. Basically everything that you go to the weather network to find out. MEDLI will look at a lot of information collected during the descent through the atmosphere. It will measure the rate that the heat shield burns up, giving an idea of how fast the temperatures change on entry. It also has sensors that are in a cross pattern that allow scientists to look at the true trajectory of Curiosity compared to the predicted trajectory that it would experience during entry. These sensors combined will allow future missions to have a more effective heat shield, along with better aerodynamics to easier control the trajectory and location of landing.

With all these sensors, if we find life (or signs of it - past or present) it is going to rock humankind hard. Depending on what the signs say, we could find that humanity originated on Mars. Or maybe there used to be Martian life, and it originated from Earth. The most exciting possibility in my mind is that life arose on Earth and Mars separately. This would demonstrate that life can happen not only once, but twice in a single solar system. And if it happens twice in our own neighbourhood, how often will it have happened on an intergalactic scale? It would bring us proof that life absolutely does exist out there.

As you can probably gather, this is going to give us the most comprehensive history of Mars that we could imagine currently. To me, the most thrilling aspect is the sensors that are looking at making future missions more efficient. This includes the thought of sending a manned mission to Mars once we have safer entry and knowledge of what to expect in the atmosphere. While finding evidence of past life would be probably the most revolutionary discovery in the history of humankind, the real revolution is in the fact that this is our first step to interplanetary manned missions. The previous rovers have kind of been like an infant crawling around on the ground, and now out of curiosity the infant has discovered that it can take steps. For the price of two coffees a year per American citizen, we can have a far more advanced rover than Curiosity ready to go in 10 years. Depending on innovations in space flight technology, we may even be ready to have a human on Mars in 10 years. As excited as I am about the steps that Curiosity is taking, I can’t wait to be running.



[1]http://mars.jpl.nasa.gov/msl/mission/instruments/radiationdetectors/rad/

Gamma Radiation

First and foremost, if you find yourself on a nuclear weapon testing site, as I know you’re wont to do, run away as fast as you can. Gamma radiation is not going to turn you into The Hulk. It is more likely to turn you into a world of hurt. Besides, do you really want to be like Hulk? Think about it, no one likes being angry. It would be a curse to only have super strength when you’re in the state of mind to hurt loved ones. I digress though.
Now that the disclaimer is out of the way, let’s start talking about some serious radiation! Gamma radiation is a little odd. It does have the highest energy and shortest wavelength of all the types of radiation (<10um), but it also has a lot of overlap with x-rays and even ultraviolet radiation. While X-rays, as we have discovered, are the result of low energy electrons, gamma radiation comes from the decay of a heavy elements nucleus [1]. The difference in origin has a tremendous impact on the radiation, as it’s even more dangerous than X-rays. There are other forms of gamma radiation as well, but I’ll get into those farther on. For now, just know that it comes from nuclear decay.
Gamma rays are produced alongside other nuclear reactions, immediately after they occur. After alpha and beta decay occurs for example, the nucleus that is left is in a higher state of energy than it was initially, and it wants nothing more than to calm down. When it looks into itself, it realizes that it’s kind of hulking out, so the nucleus will emit a gamma ray in order to calm down. This happens roughly 0.000000000012 seconds after the alpha or beta particles are shed. This is the universal rule of how gamma rays are produced, and the final statement on the matter.
Now let’s look to astrophysics, because we’re a bunch of jerks in this field. Remember how I said that nuclear reactions are gamma rays, and that’s the final statement? We’re going to ignore that entirely. Since the gamma rays that we’re detecting from space are so old, and from so far away, we don’t know if they’re nuclear or electrical in origin. Because of this, we have to go by the energy that a photon carries. That’s alright though, since things are about to get very cool.
Cosmological sources of gamma rays include such awesome (literally) sources as pulsars, quasars, supernovae, cosmic ray collisions, and the all powerful gamma ray burst (GRB). I want to talk about a few of those individually, mostly because they deserve that.
Pulsar: These tend to exist within the Milky Way as far as our observations are concerned. Think of a lighthouse on a foggy night, and the beams of light that shoot out 180 degrees from each other while rotating. A pulsar is a rotating neutron star, frequently a binary system of two neutron stars. As they rotate, their density causes a beam of radiation to shoot off in a straight line on either side of the star. When this beam points directly at us, we see a bright flash if we’re looking in the right spectrum. These last a relatively long time, and some “flash” at us so consistently that they’re as accurate time keepers as an atomic clock.
Quasar: Looking at a quasar, it may not seem too different from a pulsar in theory. They occur much farther away though, at the center of distant galaxies. As stars, planets, dust clouds, and anything else gets eaten by the central black hole, some of the energy is sent straight out in a charged beam. The lighthouse analogy works here as well, as it is two beams 180 degrees from each other. Since the quasar is much farther and larger though, the beams are much more powerful. Because the beams are so powerful though, they don’t actually pulse. It is a constant light in the gamma spectrum, and while it’s a powerful gamma blast, there’s a lot emitted in the rest of the electromagnetic spectrum as well.
Gamma Ray Burst: You don’t want to see one of these coming at you, that’s for certain. These are the most powerful sources of energy and radiation in the known cosmos. In the 10-30 second lifetime that a GRB has it will give off the same energy that our Sun will give off in it’s multibillion year lifetime, and about 50% of that will be deadly gamma rays. There are shorter length gamma ray bursts, which are believed to be from supernovae and neutron star collisions. The longer GRB is believed to be caused by a hypernova [2]. If a GRB was to collide with Earth, it would destroy all life facing it before we even noticed anything wrong.
Now, that may make you think that you never want to encounter a gamma ray in your life. And you’d be right, exposure to gamma rays are in no way good. They have some uses, such as scanning cargo containers in bulk for nuclear weapons, altering some mineral properties, and irradiate tools to kill all the life on them (you wouldn’t want an infected surgical scalpel, would you?).
So you don’t want to get hit by a gamma ray, how are you going to avoid it? For the most part, it’s not an issue. They are absorbed pretty well entirely by our atmosphere, and man made sources are strictly controlled. If you wanted to build a bunker, you could make one out of lead. But it isn’t the density of material that will protect you as much as the total mass of the oboject between you and gamma rays. 400kg of lead will only offer a slight advantage over 400kg of water or soil, so it’s much more efficient to just dig yourself to safety.
That’s about all I have to say on gamma rays, and that effectively wraps up the Electromagnetic spectrum. If any of you start turning green and strong, let me know. Because that would be really cool.

[1]Shaw, R. W.; Young, J. P.; Cooper, S. P.; Webb, O. F. (1999). “Spontaneous Ultraviolet Emission from 233Uranium/229Thorium Samples”. Physical Review Letters
[2]Tsvi Piran “The Physics of Gamma-Ray Bursts” Reviews of Modern Physics, Vol 76, October 2004

[3]http://blogs-images.forbes.com/mikemyatt/files/2012/03/Lou_ferrigno_hulk_00071.jpg?iact=hc&vpx=888&vpy=52&dur=1175&hovh=204&hovw=212&tx=169&ty=141&sig=110681999248335740788&ei=grgiUJ2RNaet6AGEh4Eg&page=8&tbnh=159&tbnw=169&start=106&ndsp=15&ved=1t:429,r:9,s:106,i:86

X-Rays

Have you ever wanted x-ray vision as a kid? Or even as an adult I suppose. I know I certainly have! Combine that with invisibility, and you have every teenage boys wet dream, right? Well, maybe not quite. X-rays are the first part of the electromagnetic spectrum that are a form of ionizing radiation. This means that they knock lose electrons, causing ions and free radicals. This is bad, and can leads to cellular mutations and cancerous growths when your body tries to repair those problems. I wouldn’t want to give people a higher risk for cancer just by looking at them, it would be like Dr. Manhattan accusations come to life. X-rays have a shorter wavelength than ultraviolet, as I’m sure you’ve figured out by now. That gives them a higher energy level. Since the wavelengths are so small (.01-10nm), x-rays are usually referred to by their energies. X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen while he was experimenting with electric currents travelling through extremely low pressure gases in vacuum tubes [1].
The name x-ray came about because it was initially an unknown phenomenon. It had to do with the electrical current producing an unknown ray, the unknown becoming “x”. In some areas, namely Germany, the rays are still known as “Roentgen rays”. Their discovery was so profoundly important, that there are still many streets named after Mr. Roentgen in many countries around the world.
Naturally occurring x-rays come from many extraterrestrial sources such as stars (neutron stars especially), some types of nebula, and black holes (kind of). Any time you have matter being superheated to millions of degrees centigrade you’re going to have emissions over a wide range of the electromagnetic spectrum, including x-rays. That explains why we can look at stars and nebulae through the x-ray spectrum. But I thought nothing could escape a black hole, how can we see the x-rays coming from them? As matter approaches the black hole, it gives off x-rays as it heats up. We may see some of these rays coming at us, but we are far more likely to see a secondary x-ray. Atoms of iron that are being pulled towards the hole absorb these x-rays that other matter is giving off, and in their newly excited state they emit x-rays of their own in a very specific frequency called the “iron lime emission” [2].
Artificial x-rays, such as the ones that are used in your doctors office, fire beams of high energy electrons at you [3]. These beams tend to pass through skin and flesh with ease, hitting a special photographic paper. When these electrons hit something with more density, such as a bone, filling, or adult toy in your carry on luggage, the electron is rapidly slowed down. When a high energy electron is forced to suddenly stop, it has to do something with that excess energy that it was motoring along with. That energy is emitted in a form we call a “characteristic x-ray” [4].
So while x-rays are ionizing radiation, we can handle them quite well in controlled doses. They’re one of the modern marvels of medicine, and I wouldn’t trade that for anything. If you were to ask what my favourite aspect of x-rays are though, I would say the aurorae (Borealis or Australis). When the rays coming from the Sun hit our magnetosphere, they are slowed down, dispersed and give off energy. When they are giving off energy in the magnetosphere most of it has nowhere to actually disperse to, so it is emitted as a lower energy in the electromagnetic spectrum, visible light. That is one of the most beautiful natural phenomena in nature, and I thank x-rays for that.

[1] http://www.nobelprize.org/nobel_prizes/physics/laureates/1901/rontgen-bio.html
[2] http://www.astro.umd.edu/~chris/Research/X-rays_and_Black_holes/x-rays_and_black_holes.html
[3] http://www.darvill.clara.net/emag/emagxray.htm
[4] http://hyperphysics.phy-astr.gsu.edu/hbase/ems3.html#c4

Ultraviolet

The next stop on our journey through the electromagnetic spectrum is ultraviolet radiation. Other than visible light, this is the most helpful for us on a daily basis, yet it’s also the most hazardous for us with our given exposure. The name ultraviolet comes from the fact that it appears immediately after what we call violet on the visible light spectrum, much like infrared means “before red”. UV rays occur in the wavelengths of 10-400 nanometres. The vast majority of UV rays on Earth come from the sun, as those of us who like long days at the beach can attest to. The ultraviolet spectrum is further separated into several sub spectrum’s, including the all too familiar UVA, UVB and UVC. There is also VUV, or vacuum ultraviolet; SUV, or super ultraviolet (not those easily flippable vehicles); and EUV, or extreme ultraviolet.
Ultraviolet A, or UVA rays, occur in the wavelength of 320-400nm. Because the UVA wavelength is close to that of visible light, it is fairly easy for it to penetrate the atmosphere and shower down on us with the visible light and warmth of the Sun. Our bodies use UVA to produce vitamin D, which is quite important for us. If you expose yourself to too much UVA though, you may end up with a sunburn, or cataracts if you’re staring at the source [1]. UVA is also emitted by blacklights, but the radiation isn’t strong enough to cause burns. It is however enough to disrupt
Of all the ultraviolet radiation that penetrates the Earths ozone layer to reach us, about 95% is UVA.
Ultraviolet B, or UVB, is mostly absorbed by the atmosphere although a significant amount still reaches us. When you wear sunscreen, UVB is the important UV that it blocks. UVA may cause the actual burn, which sucks, but UVB rays are the ones that can lead to cancerous cells. UVB radiation is the leading non melanoma cause of skin cancer, and can make melanomas worse [2]. Your hair and clothing are pretty close to 100% effective at blocking UVB radiation, but exposed skin and eyes are highly susceptible to the damaging effects. Combine that with the fact that you don’t want to wear a parka on a sunny day, and you have a recipe for disaster. The danger of UVB rays comes not from the fact that it’s ionizing, because ultraviolet rays are in fact non-ionizing, but because they disrupt your DNA. When you are exposed to UVB, your DNA strands have a chance of “unzipping” in certain sections, and recombining to itself as opposed to its proper opposite strand. Your cells do have a mechanism to counteract this effect, but it is quickly overwhelmed if you aren’t careful. UVB is emitted artificially by blacklights and wielding torches. In blacklights again, the amounts are small enough to be considered safe in your home. A wielding torch though gives off enough UVB radiation to be dangerous to exposed eyes, hence wielders wearing face plates and goggles with very thick and dark glass.
Ultraviolet C, or UVC, is the most damaging form of ultraviolet radiation that you are likely to encounter. While this is emitted by the Sun, it is for all intents and purposes completely absorbed by the ozone layer [1]. The only problem is UVC has some very practical commercial and private uses, so it is still possible to be exposed to these rays. You may have heard of ultraviolet disinfecting, and this is done using light in the UVC range. It is so good at killing life at the cellular level that it is used to disinfect many surgical tools. If you have a pond or fancy aquarium, you may use a UV filter to clean the water, this also uses UVC rays to kill any form of bacteria that may be present. Short term exposure to these rays is safe, but if you were to leave the light shining on you for any extended periods of time, you’re risking damage on the cellular level which is what increases chances for cancer to develop.
VUV, or Vacuum ultraviolet is used in spectographic analysis. It is important to note that while UVC and higher energies of the ultraviolet spectrum are absorbed nearly entirely by ozone and oxygen, they can be used for scientific purposes in a vacuum. The technology to use VUV has increased, and it has been realised that to cut costs on equipment that would have to be strong enough to withstand a vacuum, non oxygen materials such as nitrogen can be used as a medium for UVC and VUV to travel through essentially unhindered [3].
A few of you astute readers may have noticed a connection between what I’ve been talking about, and a major talking point of the 1990’s. I mentioned the ozone layer a few times in this article, and the fact that it absorbs a lot of the UV rays that are hurtling towards us. Many people seem to equate ozone depletion that is happening in the antarctic and arctic with global warming, but it is a different phenomena with different causes and results. As the ozone layer depletes, it isn’t adding to the warming planet, but it is letting extra UVA and UVB through to the surface of the Earth. While this may mean high cases of cancer amongst us humanfolk, it can have a devastating effect on the biosphere. If the ozone holes grow larger or last for longer periods, more UV rays will make it to the ocean surface.
There are many small creatures and plants that live near the surface of the oceans, such as phytoplanktons and cyanobacteria. Cyanobacteria in particular are the base of the oceanographic food web, and they get their energy through photosynthesis. As they are exposed to excess levels of UV rays, they suffer deformities and begin to die off [4]. If this were to happen on a large enough scale, it would devastate many ocean based communities. Without reaching too far into other implications such as oxygenation and warming waters, it would have an immediate impact on humanity through a sudden drop in fish populations on coastal towns, which are still the most populous and productive areas of human communities. I don’t think I’m saying anything controversial with the fact that crippling humanities most productive sector is a bad thing, but much like global warming, there has somehow been debate on the topic. Even if you don’t think ozone depletion is man made, or a bad thing, what’s the worst that happens if we try to stop it? We accidentally create a better world in the process?
Sorry to end on a bit of a moral lesson, but ozone depletion took a back seat to global warming in the 2000’s, and I think both are extremely important issues and neither should be ignored. It seems like a slippery slope when we ignore one potential global disaster because a new one enters our line of sight. I’m worried that in 10 years we’ll forget about global warming when a new hot button issue comes along, and we’ll not have corrected warming or ozone depletion.

[1] http://www.nas.nasa.gov/About/Education/Ozone/ozonelayer.html
[2] http://www.who.int/uv/health/en/
[3] "vacuum-ultraviolet radiation." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. 19 Feb. 2012. <http://www.britannica.com/EBchecked/topic/621412/vacuum-ultraviolet-radiation>.
[4] http://www.ncbi.nlm.nih.gov/pubmed/15986833

Visible Spectrum

[1]

What colour is your shirt today? Whether it’s black, white, blue or red, it’s visible. Today we’re talking about things that you and I can see. Specifically, the visible spectrum of light. Also called the optical spectrum of light, this is the wavelength that is visible to our eyes (via the cones). The most convenient way to start this off is to talk about the rainbow. Starting from the top, the colours on the rainbow are red, orange, yellow, green, blue, indigo and violet. Every one of those colours has a different wavelength (740nm, 625nm, 590nm, 565nm, 520nm, 500nm, and 435 respectively [2]).

Most of the light that we encounter in our day to day life is white, and in fact all light originates as a white light. We see the different colours of the rainbow when an object reflects or refracts a specific wavelength of the white light. The orange that you have in your kitchen is that colour because an orange absorbs all the wavelengths of visible light except for the 590nm-625nm range, which gets reflected into your eyes. That is how most of the objects are perceived as colour to us. This also explains why the leaves on the trees change colour in the fall. Chlorophyl (which you may recognize as the chemical that allows photosynthesis) absorbs all the light except for green, but as the hours of sunlight decrease in fall they stop producing chlorophyl, when carotene and anthocyanins remain the only chemicals. Carotene makes the leaves appear yellow and orange, while anthocyanins cause the reds and purples.

That absorption and reflection of light is only a partial story about why we see rainbows as a beautiful series of colours though, nothing else in nature really occurs like a rainbow does. That’s because white light has an interesting property when shining through a prism. It will refract the range of wavelengths that are contained in white light to separate the colours perfectly (as is demonstrated on Pink Floyds Dark Side of the Moon album cover). A rainbow occurs when water particles in the air act as the prism and separate the wavelengths on a large scale. You see the same exact effect when you play with a hose on the mist setting on a sunny afternoon.

One of the most interesting aspects of visible light in my opinion is the colour magenta. It is a colour that doesn’t actually have a place on the electromagnetic spectrum. How can this be possible? What is a colour if it doesn’t actually exist? That’s because every colour on the EM spectrum has a complimentary colour, which is the colour you will see if you stare at something long enough and then take it away (ie, blue and green mixed together will produce a cyan colour). The complimentary colour to green though exists between red and blue, and as we learned above they exist on opposite ends of the visible light spectrum. Magenta is your brains best estimate to what the naturally occurring compliment would be for green.

[1]http://mirror-au-nsw1.gallery.hd.org/_c/natural-science/prism-and-refraction-of-light-into-rainbow-AJHD.jpg.html

[2]http://physics.about.com/od/lightoptics/a/vislightspec.htm

[3]http://chemistry.about.com/od/colorchemistry/f/how-magenta-works.htm

[4]http://chemistry.about.com/od/colorchemistry/f/how-magenta-works.htm

Infrared

[5]

Wavelength: 7 x 10-7 - 1 x 10-3 m

Frequency: 3 x 1011 - 4 x 1014 Hz

Energy: 2 x 10-24- 2 x 10-22 eV

Infrared (IR) is the closest to visible light we’ll get to on this end of the spectrum. At it’s shortest wavelength it is just bordering on what we can see with the naked eye. The IR radiation can be broken up further into the following spectrum:

Near Infrared: 0.7µm - 1.3µm wavelength

Short Infrared: 1.4µm – 3µm wavelength

Mid Infrared: 3µm - 8 µm wavelength

Long/Thermal Infrared: 8µm - 30µm

Far Infrared: 15µm – 1000µm

Astronomers divide the spectrum differently, usually as follows [1]:

Near IR: 0.7 µm – 5 µm

Mid IR: 5 µm – 40 µm

Far IR: 40 µm – 350 µm

Mid Infrared and Long Infrared are emitted by an object naturally, while Near Infrared and Short Infrared are reflected off an object.

IR was first theorized by Emilie du Chatelet in 1737 in a paper titled Dissertation sur la nature et la propagation du feu. Her theory was proved correct in 1800 when William Herschel published the first record of experimental proof of IR radiation.

The most common type of IR radiation that you or I would recognize is heat. IR radiation from the Sun provides Earth with 49% [2] of its heat, with thanks to greenhouse gases. Without any of those, no IR heat would be absorbed and slowly released back into our lower atmosphere to keep us at our cozy temperature.

Without IR radiation, we wouldn’t be able to use nightvision technology. Both traditional nightvision and thermal imagine use light in the IR spectrum to enhance images in otherwise dark areas. The absorption of IR into clouds and the atmosphere allow our weather satellites to make mostly accurate weather predictions that you end up seeing on the nightly news. In astronomy, IR can be used to measure through clouds of molecules, nebulae, and detect redshifted objects [3].

Blackbody radiation is the natural amount and type of electromagnetic radiation that an object absorbs at any given temperature above absolute zero. At Earthly temperatures, blackbody radiation exists in the IR range [4], as that is the only range on the spectrum that it won’t absorb entirely.

Some animals have evolved natural mechanisms that allow them to detect IR light. These animals include pit vipers, pythons, some boas, vampire bats, and some insects. It is unknown the degree to which these animals can sense IR light, but there’s no doubt that it must help them hunt prey or avoid predators!

[1]http://www.ipac.caltech.edu/outreach/Edu/Regions/irregions.html

[2]Passive Solar Heating & Cooling Manual. Rodale Press, Inc.. 1980. Retrieved 2007-08-12 

[3]http://www.ipac.caltech.edu/outreach/Edu/importance.html

[4]http://galileo.phys.virginia.edu/classes/252/black_body_radiation.html

[5]http://www.medcatalog.com/images/Meditherm.gif

Back to basics

Let’s take a step back and talk about the most basic measurements in physics. Measurement and observation are the two most important parts of science, bar none. Without observation, we would have no way to verify our theories. Whether you prefer theoretical or experimental physics, both of these aspects are critical. Right now I’m going to discuss the basics of measurement.

The four most important measurements you will ever need in physics are speed, volume, density and acceleration. Almost any equation you look at will feature some of these four in a large way. You can find these using length (metres or m), time (seconds or s), and mass (kilograms or kg). The different combinations of these base measurements will give you anything you need to know about an object.

To find the speed of a given object, you must divide the distance (length) an object travels by the amount of time it took said object. If a car travels 132km in 92 minutes, the equation would look like:

v=112km/92min

v=1.2km/min, therefore it would be travelling at 1.2km/min. To turn that into kilometres per hour, we just need to multiply by 60 (as there are 60 minutes in an hour), for an answer of 72km/hr. Of course, this is assuming that the car was travelling at that speed from the first moment of measurement.

To find the acceleration of an object, you must divide the change in velocity by the time it takes for that change to occur (a=Δ v/t or a=[v2-v1]/t). To find the rate of acceleration of the car above, we’ll say that it accelerated from 0km/hr to a speed of 72km/hr in 8 seconds. Using the equation above, we’ll find:

a=[72km/hr-0km/hr]/8s

a=[72km/hr]/8s

a=9km/hr/s

With that, we know that if the car accelerated constantly, its speed increased by 9km/hr every second. Of the four basic measurements, acceleration is probably the hardest for most people to wrap their minds around as it includes two separate measures of time.

Now, let us assume that we have a very poor auto designer that made this car, and it is a perfect rectangle. It is 3m long, 1m wide and 1.5m tall. If you want to know the volume inside the car, you use the equation x=(l)(w)(h), or volume=length times width times height. So for this car, it would be:
x=(3m)(1m)(1.5m)

x=4.5m^3

So now we know the car has 4.5 metres cubed of space.

Now we want to know how dense this brick of a car weighs! I’m going to tell you that the vehicle weighs 500kg. We know that it has a volume of 4.5m^3, and with those two pieces of information I can show you how to find the density! It’s quite simple actually, it is just d=m/v, or density equals mass divided by volume. Let’s just go right ahead and plug numbers into the equation:

d=500kg/4.5m^3

d=111kg/m^3

Now we know that the car has a density of 111kg for every metre cubed of space, it has 4.5 cubic metres of space, it can accelerate 9km/hr/s, and travel 72/km/hr.

With all of the above measurements, you can find out how much cargo you can fit in a ship, how much fuel per kilogram of mass you’ll need to launch out of the Earths atmosphere, how long you’ll have to accelerate to get to a cruising speed, and how long it will take to travel the distance to Mars at that speed. You can then figure out deceleration for landing and the weight of the cargo and astronauts under the new gravity on Mars.

Now there is one important aspect to measurements like this that I haven’t mentioned, as it isn’t important for hypothetical scenarios like the car above. It is the uncertainty of a measurement, or sometimes referred to (incorrectly in my opinion) as an error in measurement. If I wanted you to find the density of the car, and I only knew the mass give or take 100kg, you wouldn’t be able to find the exact density. That is alright in measurements, but you have to take that into consideration as a +/- factor so that you can be aware of the 200kg (100kg over 500kg, 100kg under 500kg for a total difference of 200kg) gap.

Microwaves

Wavelength: 1 x 10-3 - 1 x 10-1 m

Frequency: 3 x 109 - 3 x 1011 Hz

Energy: 2 x 10-24- 2 x 10-22 eV

Microwaves are the next stage of electromagnetic radiation. They have wavelengths from 1mm to 1m and frequencies from 0.3GHz to 300GHz. This puts them in between radio waves and infrared on the EM spectrum. Jagadis Chandra Bose was the first person to really experiment with the EM spectrum in the microwave range. In 1895 and 1896, before Marconi was credited for the first radio message, Bose sent information over a mile using microwaves in the 2-5mm wavelength [1]. This makes him the first person to use radio waves to transmit information.

Microwaves pass through clouds, fog, clothes, and most non metal materials with relative ease which makes them excellent for communications[2]. They don’t penetrate most metal materials however, which means containing them in a metal area (such as the walls of a microwave oven) will concentrate the waves, making them more powerful. Anything with a high enough water content will absorb microwaves, causing the particles within to vibrate and give off heat. This is the basic principle that a microwave oven uses to cook your food, and it’s also why the tupperware containers that you throw in there won’t heat up.

Other than the microwave oven, sources of microwaves include the maser, which is similar to a laser but it concentrates microwaves as opposed to visible light, the sun and other celestial objects, and Cosmic Microwave Background Radiation (CMB). The CMB was detected in 1964 by Arno Penzias and Robert Wilson [3], and it is a nearly uniform level of microwave radiation everywhere in the universe. The equal levels in all directions is one of the huge proofs for the Big Bang, or Big Expansion.

Household wireless communications, from modems and routers, cell phones, cordless phones, and nearly any other cordless technology uses microwaves in the 2.4GHz to 4GHz range (Take a look at your cordless phone, odds are it will say 2.4 on it somewhere, unless it’s a newer phone which might have 4.something on it. That’s the frequency that it uses).

Microwave radiation is a non-ionizing radiation, which means that it is not powerful enough to knock electrons away from particles. That is how stronger forms of radiation lead to cancer, so sitting in front of your microwave is almost universally considered to be safe. The harm that could come from concentrated microwaves such as in the microwave oven would be from the excitement of water particles, which would essentially cook whatever they hit. Again though, it has to be on the powerful end of microwave radiation and concentrated to have that effect.

[1]http://www.tuc.nrao.edu/~demerson/bose/bose.html

[2]An introduction to atmospheric radiation, Kuo-Nan Liou, pg349

[3]http://aether.lbl.gov/www/science/cmb.html

Radio Waves

Wavelength: > 1 x 10-1 m

Frequency: < 3 x 109 Hz

Energy: < 2 x 10-24 eV

Continuing on with the Electromagnetic Spectrum (to be called EM spectrum from now on) topic, today I’ll talk about radio waves specifically. They are the longest waves in the EM spectrum, having a wavelength from the size of an American football to an American football stadium. Since it is made of photons, the waves travel at the speed of light, which is pretty damn fast. Artificial sources of radio waves include radio towers (duh.), RADAR, satellite communications, garage door openers, and many many other sources. Naturally produced radio waves come from sources such as lightning strikes and astronomical objects.

Radio waves were first predicted to exist theoretically by James Clerk Maxwell in 1865[1]. He noticed a striking similarity between the behaviour of visible light, and electronic/magnetic waves. In 1887 Heinrich Hertz generated the first radio waves experimentally, which launched into an age of radio communications. I think we can all agree that this was a positive step for humanity.

Different frequencies of radio waves behave differently. They reflect, refract, polarize, diffract and absorb into the surroundings in different ways. Because of this, different frequencies have different specialized uses. Radio waves that you use to listen to music and talk radio are intercepted by an antenna, and then a tuner resonates at the specific wavelength frequencies to make one station stand out above the rest[2]. Radio wave are also used in medicine for the treatment of sleep apnoea, in MRI’s, and for bloodwork. My personal favourite use of radio waves though is in radio astronomy. Using radio satellites, scientists can look at objects in the sky with an amazing amount of accuracy, since objects in space give off radio waves. Some of the wavelengths of these objects can actually extend longer than a mile![3]

That’s all I have to say on the topic of radio waves. Those of you that are clever can probably guess my next topic. It rhymes with Dicrodaves.

[1]http://www.juliantrubin.com/bigten/hertzexperiment.html

[2]http://www.infoplease.com/ce6/sci/A0860617.html

[3]http://science.hq.nasa.gov/kids/imagers/ems/radio.html

Electromagnetic Spectrum

Cosmic Microwave Background

http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation

If you’re looking at a monitor of some sort right now, you have electromagnetic radiation to thank for that. The electromagnetic spectrum ranges from radio waves to gamma rays, and is responsible for a surprising amount in between. Everything on this spectrum is a form of radiation, although most of it isn’t harmful to us.

The entire spectrum is composed of photons, which are particles of light. They are measured by their wavelength, frequency, and energy. The wavelength is a measurement from the peak of one wave to the peak of the next, and on this spectrum can range from Nanometres (one billionth of a metre) to 100+ metres(m). The frequency of a wave is how many peaks pass a certain point per second, and is measured in hertz (Hz). Lastly, we have the measurement of energy. This is simply how much energy the photons have, measured in electron volts (eV). You can find the energy of a photon using the equation E=(h)(c)/λ. E is equal to the energy (eV), h is Plancks constant, c is the velocity of light (just like in that good ol’ E=mc^2 equation), and λ is the wavelength (the symbol is called Lambda. You don’t need a crowbar to open up this symbol).

If you plug the numbers into the above equation, you’ll quickly find that the wavelength and frequency are inversely proportional, which is also common sense once you think about it. A wave that is 100m long will pass an individual point less times per second than a wave that is 1nm. Something strange does happen with the different wavelengths and energies though. The lower end of the spectrum with low energy has the photons behaving as a wave, whereas the high energy end of the spectrum has the photons behave as particles. This is called wave-particle duality[1], and is responsible for the famous Double Slit experiment.

I think it’s about time to get into the actual types of radiation all along this spectrum.

Radio waves: That’s right, listening to the radio is a form of electromagnetic radiation. This is also where over the air TV signals come from, and a lot of phone signals. I couldn’t imagine the world today without these wonderful waves. They have the longest wavelength, reaching 100m and higher.

Microwaves: Another convenience of the modern world, microwaves are here too. In addition to cooking your food, telecommunications satellites use microwaves to get signals down through Earths atmosphere, it’s used in RADAR and it has a strong Doppler effect. My personal favourite part is the Cosmic Microwave Radiation that we are now able to detect everywhere in the universe, which tells us a lot about the Big Expansion.

Infrared: This is in your remote control for your television. It’s also the heat from the Sun, the police use infrared cameras before they bust your grow op, and some animals such as snakes can see in the infrared range.

Visible: As useful as the previous types have been, this is the one that we’re the most familiar with. We see in this range of light. When you’re looking at what colour anything is, you’re seeing the light that is reflected off that object. Within visible light, the spectrum goes Red, Orange, Yellow, Green, Blue, Indigo, Violet. You may know those colours as Roy G. Biv, or the colours of the rainbow. Red has the longest wavelength, and violet has the shortest. Now the names of the previous and next items make sense.

Ultraviolet: This is the one that makes a lot us hate the Sun. If you’ve ever had a sunburn, you have ultraviolet light to thank for that one! The ozone layer blocks most of the ultraviolet light which we can be thankful for, but enough gets through to be a pain in the skin. Some insects have the ability to see in the ultraviolet spectrum, and you’ve probably seen them use UV lights in shows like C.S.I.

X-Rays: If you’ve ever broken a bone, you know about these first hand. X-rays are a very high energy form of radiation, and occurs naturally in space. Luckily our atmosphere blocks almost all of the x-rays from hitting us. This is a form of Ionizing radiation, which means that it knocks electrons lose. These electrons flying around in your body can break DNA cells, which sometimes repair with mutations. That’s called a cancerous cell, and it’s a good idea to avoid getting those.

Gamma Ray: Watch out, Radioactive Man! This is the big daddy of the electromagnetic spectrum. You want to avoid gamma rays at all costs, as they are even more energetic than x-rays. These have a wavelength in the nanometre range, and will cause you lots of trouble. They are caused by nuclear explosions and radioactive atoms. They do occur naturally in space quite frequently, which is a danger for astronauts who don’t have our atmosphere to protect them. One of the most devastating forces in the universe is called a Gamma Ray Burst, and it is a huge beam of gamma rays that flies in a single direction killing everything in its path. In my attempt to be a fear monger, I’ll let you know that it’s possible for one of these bursts to hit Earth at any moment, without warning, killing everything that is facing the burst instantly. On the plus side, because gamma rays are so energetic, they can also be used to destroy cancerous cells in some forms of treatment.

Below is a table listing all the wavelengths, frequencies, and energy levels of the different types of radiation. [2]


Wavelength (Hz) Frequency (m) Energy (eV)




Radio

> 1x10^-1 Hz

< 3x10^9 m

< 2x10^-24 eV

Microwave

1x10^-3 - 1x10^-1 Hz

3x10^9 - 3x10^11 m

2x10^-24- 2x10^-22 eV

Infrared

7x10^-7 - 1x10^-3 Hz

3x10^11 - 4x10^14 m

2x10^-22 - 3x10^-19 eV

Visible

4x10^-7 - 7x10^-7 Hz

4x10^14 - 7.5x10^14 m

3x10^-19 - 5x10^-19 eV

Ultraviolet

1x10^-8 - 4x10^-7 Hz

7.5x10^14 - 3x10^16 m

5x10^-19 - 2x10^-17 eV

X-ray

1x10^-11 - 1x10^-8 Hz

3x10^16 - 3x10^19 m

2x10^-17 - 2x10^-14 eV

Gamma Ray

< 1x10^-11 Hz

> 3x10^19 m

> 2x10^-14 eV

[3]

[1] http://physics.about.com/od/lightoptics/a/waveparticle.htm

[2] http://imagine.gsfc.nasa.gov/docs/science/know_l1/spectrum_chart.html

[3] http://science.hq.nasa.gov/kids/imagers/ems/index.html