Ozone: Nature’s Sunglasses

Posted on June 21, 2013 by danielfeldman

I think most people know about the ozone layer of our atmosphere. It’s supposedly this thin layer of atmosphere that protects us from getting sunburnt while we lay out on the beach with intentions of becoming oompa loompas (though for many of us, we still end up looking like tomatoes after a few hours). But what is ozone and how does it actually protect us? And why did we make such a fuss when a hole was discovered in the ozone layer?

Ozone is a molecule made up of 3 oxygen atoms (O3). There are actually 3 flavors of Oxygen in our atmosphere–there’s atomic oxygen (O), diatomic oxygen gas that we need to survive (O2) and ozone. There’s not all that much ozone in the atmosphere–it’s just a thin  gaseous layer found in the stratosphere, which is located between roughly 10 and 50 kilometers above the Earth’s surface (right above the troposphere, where weather occurs).

So how does it form? Ozone forms from a chemical reaction that occurs during a 3 molecule collision. One oxygen atom must “collide” simultaneously with an oxygen molecule and a third atom/molecule, which we’ll call Herman. When these three things collide, the oxygen atom and molecule fuse together to form ozone, and Herman flies off unaffected.

And now Herman is no longer happy.

And now Herman is no longer happy.

Ozone is also destroyed naturally. This happens when ozone interacts with energetic particles of light. In chemistry, there are reactions called photodissociation. This is when a molecule collides with a very energetic photon of light, absorbs its energy, and splits apart (dissociates). For ozone in the atmosphere, it will often interact with incoming Ultraviolet (UV) radiation from the Sun, absorb the UV light, and then split back into the oxygen atom and molecule. Because this happens a lot, ozone absorbs a lot of the Sun’s incoming UV radiation, and is therefore an essential piece of protection for plants and animals against UV radiation, which in high doses is highly dangerous!

This is why we like ozone.

This is why we like ozone.

Both creation and annihilation of ozone occurs naturally, and there is a natural balance that keeps the ozone layer healthy. But humans ruined everything, as we always do. There are compounds that used to be used heavily in aerosol sprays and refrigerators called chlorofluorocarbons, or CFCs (sometimes known as Freon). Chlorofluorocarbons, as you may guess, are molecules made up of chlorine, fluorine, and carbon. CFCs are dangerous because they can react with ozone in a way similar to the way Herman did. In chemistry, many reactions are reversible, which means that you can have a reaction go backwards until there’s an equilibrium. Earlier we discussed how oxygen atoms and oxygen molecules can collide with Herman to produce ozone and a slightly annoyed Herman. Well it can go backwards, and Herman can bang into ozone to make an oxygen atom and molecule. And sure enough CFCs can play the role of Herman and act as a catalyst for that reverse reaction, destroying ozone. And unlike the photodissociation reaction, where the UV photon is destroyed as well, the CFC reaction keeps CFC in the atmosphere, allowing it to further destroy more ozone! As a result, we created a large hole in the ozone layer.

Pure molecular evil.

Pure molecular evil.

Our story does get a little better though. In what scientists call “a political miracle”, a UN treaty saw agreeing governments drastically reduce the use of CFCs in aerosols and such in an attempt to solve the problem we created. And after much sweat and worry, the ozone depletion scenario is beginning to improve!

So to recap, ozone (O3) is created naturally and destroyed by UV light, which offers protection to living things, since UV light is dangerous and gets absorbed by ozone photodissociation. We created a hole in the ozone layer with the usage of CFCs, but then we drastically reduced our usage of them and the problem is getting fixed. Moral of the story, when humans are destroying our world by putting dangerous molecules in the air, the problem can be at least partially mitigated by action to reduce the amount of said molecule in the atmosphere. Sound familiar? Now if only we could convince legislators to address other pressing scientific problems pertaining to our atmosphere…

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Does Science Ruin Beauty?

Posted on June 6, 2013 by danielfeldman

I think we’ve all heard or said this before: “Don’t tell me how it works–you’ll ruin the beauty of it.” As if knowing what causes a phenomenon will suddenly make it dull and boring. Yeah, maybe if the person telling you about it is boring. It’s almost maddening how dull scientific papers are, how science teachers often suffer from the “well actually…” syndrome, or how uninterestingly science can be presented to a general audience by scientists who decide that communication is a skill best left to the journalists (God forbid they should have any kind of similarities to the humanities). But science is not boring and it is certainly not ugly.

Have you ever looked up at a dark night sky? Seen the beauty of the thousands of suns beaming their energy at you from unimaginable distances, or the glow of the Milky Way in all of its nebular glory, a dazzling palette of color streaking across the canvas of the heavens? It’s quite a sight to behold. The starlight entering your eyes traveled distances so unbelievably far that for all its incredible speed, the light took years, decades, centuries, or even millennia to reach your retina. When you gaze at these brilliant specks, you see light that was emitted when your parents were born, your grandparents, your ancestors going back into the bygone eras. These rays of light were partly emitted during the fall of Rome, the days of Pythagoras, the building of the Pyramids of Egypt. Some of the fuzzy galaxies, incredibly small to your naked eye but incredibly large in reality, emitted the light you see at the time when dinosaurs once roamed the Earth. Despite all of our greatest telescopic technologies, we cannot glimpse the stars (other than a small few) as anything more than points of light. But they are so much more—Betelgeuse in its red fire is so large that if you plopped it where our Sun sits, it would fill up the entire space in our solar system out to Jupiter, engulfing the asteroid belt and all the inner planets. Its “surface temperature”, despite its enormous brightness and size, is cooler than that of our timid Sun, and so it appears red. Other stars however, are much hotter, and so they appear blue. When I look up at the Milky Way, I see much more than just colorful gaseous puffs—I see stellar nurseries, clusters of stars, gas and dust, and even cosmic cemeteries. But knowing these wondrous things ruins the beauty of the night sky?

How about a rainbow? Surely you would agree that rainbows are some of the most impressive sights to behold. But why is that? After it rains, there remains a lot of water droplets suspended in the air. These droplets reflect and refract sunlight at a sweeping number of angles, dispersing the white light into its many colors and forming a rainbow. Sometimes you get multiple reflections, and can get double rainbows. Because it’s all about light bouncing around at angles into our eyes, rainbows aren’t physical objects, so you can’t approach a rainbow, or follow it to the end and find a pot of gold. But you can see some majestic displays of every color. Does understanding optics really take away from the wonder of a rainbow?

As children we approach the world with a natural ignorance and wonder, stemming from an appreciation for the beauty of things around us and the desire to learn all about what makes the magic we perceive. But then for some reason, as we age, we tend to lose that second essence of nature—we decide that ignorance is better, that it no longer matters why something is so beautiful, only that it is. We decide, having perhaps grown spiteful of our knowledge of adult problems and frustrations (i.e. the end of youthful bliss), that further illumination would be a fate worse than the blind acceptance of all that is seen by our eyes.

But it doesn’t have to be this way. We can put an end to this myth, right here and now. Science is not ruining the beauty of nature—it is the beauty of nature. Things you experienced as a child are just as amazing as they were when you were five years old. Rainbows, night skies, the vortex that forms during the draining of a bathtub, the uniqueness of snowflakes as they fall to their eventual melting, the green patina engulfing the once-copper-brown Statue of Liberty, the fish fossils found at the tops of mountains, all of it…the amazement found in the world we inhabit is derived not only from the external beauty, but from the intrinsic, wonderful “magic” of the science underlying all of nature. And that, my friends, is beautiful.

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Productivity (Circa Summer 2012)

Posted on June 4, 2013 by danielfeldman

Back in the summer of 2012, while working at the American Museum of Natural History (AMNH) and putting the finishing touches on my senior thesis, I was faced with a 3 week period without my advisors around. At the time I was studying the atmospheres of brown dwarfs (stars not massive enough to fuse hydrogen in their cores) with the group BDNYC, and studying specifically the absorption profile morphology of neutral potassium in their spectra. I had a few things to do while my advisors were away–I had to finish editing plots in my thesis, work on updating our brown dwarf database, and look into placing the brown dwarfs in my sample with Associations (groups of stars that move together and share the same rough age estimate). However, my productivity was less than stellar (much like my brown dwarfs, BAM!) due to the fact that it was summer and I came down with some illness I don’t remember. I kept a research journal that tracked my progress, and as such, needed to present said progress after the 3 week hiatus of my advisors at our group meeting. Determined to have a graph to bring to group meeting, I drew the following graph of my productivity:

The title is "Dan's Productivity", which is obscured by the tape holding it to my desk wall.

The title is “Dan’s Productivity”, which is obscured by the tape holding it to my desk wall.

The x axis represents time in number of weeks ago (3 being when they left, 0 being present, i.e. the group meeting). The y-axis represents my productivity in terms of typical productivity language. As you can see, science research can have its ups and downs of research productivity.

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Tales of Comet Tails

Posted on May 17, 2013 by danielfeldman

(This entry caps off my Facebook “fun facts” series from my studying for a brutal comprehensive exam for graduate school, and is inspired by an old comps problem on Comet Hyakutake. And it’s an excuse to look at so many pretty pictures of comets. Enjoy!)

Going back to the early days of recorded history, mankind has always been fascinated by comets. Despite their incredible beauty, they were almost always seen as bad omens. Big events can be traced back to events of comet sightings…and then there are comets in popular culture. Overall, comets are a huge source of wonder to people of all ages, but have you ever wondered why they look so beautiful? What causes those long, majestic tails? And have you ever noticed that comets actually have two tails? That’s right—comets have two tails! Each tail is caused by a different process…one is caused by the light from the Sun, while the other is caused by the solar wind.

Let’s first look at a comet’s dust tail. Comets are essentially large balls of ice with long, elliptical orbits—as they sweep inwards towards the inner solar system, the icy material on their surface heats up and begins to sublimate (go from solid to gas) off the surface. This forms a gas cloud of gaseous water, carbon dioxide, and other icy molecules around the comet nucleus. This cloud is called the comet’s coma. If you remember from my entry on the Crookes Radiometer, light exerts a pressure, and can push on things. Similar to how it pushed on the radiometer panes, radiation pressure pushes out the gasses of the coma as well as the dust on the comet’s surface, forming the dust tail! The dust tail is typically redder in color, because it preferentially reflects red sunlight. This radiation pressure not only creates the dust tail, but also pushes it into a curved shape!

Light, however, is not the only thing comets have to deal with as they hurl into the inner solar system. In addition to sunlight, our beloved star is constantly ejecting energetic charged particles outward, at speeds of  approximately 250 miles/second! Comets are therefore getting rammed by this energetic solar wind, and it doesn’t go unnoticed. As solar wind particles slam into the comet’s nucleus and coma, they undergo a process with the gas called charge exchange, in which the charged wind particle steals an electron from a neutral gas particle. The now neutral wind particle flies off as an energetic neutral particle no longer affected by electromagnetic forces, but the now-charged gas particle gets swept up into the solar wind!

The solar wind is a real ion player, picking up all those ions.

The solar wind is a real ion player, picking up all those ions.

Because these charged particles are swept up into the solar wind, and are now going to spiral around the interplanetary magnetic field lines (yes, there’s a magnetic field that permeates the solar system!), the new pick-up ions from the comet form a distinct, sculpted tail called the ion tail!

Unlike the dust tail, a comet’s ion tail preferentially reflects blue light, so it will be bluish in color. And since its formation and movement depend on totally different processes than the dust tail (light pressure versus particle ram/magnetic interactions), it is often a bit separated from the dust tail. As a result, most comets will have two very distinct tails that you can tell apart. These tails are huge, and can be up to an entire astronomical unit in size (1 astronomical unit is roughly 93 million miles long — it’s the distance between the Sun and Earth).

But there’s a final piece to our dazzling story of comets. Comets are often confused with meteors, and for good reason—both are objects in the sky that are relatively small and have long streaked tails. The only difference (visually) is that meteors disappear really fast, since they are actually chunks of dust/rock/ice that enter Earth’s atmosphere and burn up, whereas comets are not actually in Earth’s atmosphere but are just physically large and bright. But these two seemingly unrelated objects share a very intimate connection…meteor showers are actually the debris of comets!

How is this possible? Well, we already discussed the comet tails and how they form, but what actually happens to the material in the tail after it gets blown off the comet? The ion tail is the easiest—since it’s swept into the solar wind, it does what all solar wind particles do—follow along magnetic field lines and sweep out to the far reaches of the solar system. But what about the dust tail? The dust tail is neutral, and so all the dust, rock, and ice ejected from the comet just goes into orbit around the Sun, trailing behind the comet. Since the tail is so long, this dust reaches all the way out into Earth’s orbit and beyond.

You can think of comets as being like dirty children coming into the house after rolling around in dirt. As they run in and begin wreaking havoc, they start spraying dirt all over the floor. You can track where they’ve been by the trail of dirt that they leave behind. So what do you do? You clean it up! In some sense, the Earth is like a giant vacuum cleaner. As it follows its orbit around the Sun, all the left over comet debris will fall into the atmosphere and burn up—causing a meteor shower! So when you see these meteor showers, you are actually just seeing the burn up of cometary debris. So even though meteors are not comets, they do originate from comets!

Let’s face it…comets are awesome. And though they may be a big threat to our existence (they may have killed the dinosaurs), we love them anyway. Next time a comet passes by the Earth’s neighborhood (and they do often), get your butt to a telescope!

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