Tag Archives: Nature

What Color is Lightning in a Beaker?

Thunderstorms can be incredible to experience. From the bright flash of lightning that is often almost to fast too see, to the immense crack of nearby thunder that can make your heart feel like it skips a beat, they truly are a demonstration of the power of nature.

lightning

Image Credit: NASA

They are also full of interesting science! For instance, lightning usually carries between 100 million and 1 billion volts of electricity! This allows it to jump all the way from clouds to the ground, and as it does so, some of that energy is transferred to the atoms in the air. This energy is released as light, which is how we see it. 

This means that it is the air itself which determines what the air looks like. On Earth, our air is made up of about 78% nitrogen, 21% oxygen, and a bunch of other gases like water vapor, carbon dioxide and argon. When we put electricity through it, it gives off a characteristic glow:

lighting1-smaller

The Oudin Coil generates up to 50,000 volts of electricity–much much less than a thunderstorm. This allows the electricity to jump about an inch, rather than the miles between clouds or to the ground of an actual lightning strike. However, when it arcs through the air, this still produces a similar look and identical color1.

Lets see what it would look like in a different environment. The beaker in this gif has a bunch of dry ice–which is just solid carbon dioxide–at the bottom. Unlike regular ice, dry ice doesn’t turn into a liquid, but instead skips straight to carbon dioxide gas! This gas is more dense than air, so the beaker ends up full of just carbon dioxide, which is a much different composition than our atmosphere. Check out what happens to the lightning in there!

color-change

Unfortunately, we can’t try this particular method with every gas for several reasons. First of all, not all gases are heavier than air. This would make it hard to keep it in the beaker. In addition, other gases might explode, or worse, if exposed to electricity with oxygen around in this way. Still other gases can be very toxic. Fortunately, we have some tubes of gas and a machine that puts electricity through it in a similar way. In this gif, the gas tubes are viewed through a diffraction grating which breaks up the light into the different colors of the rainbow contained within. This is actually a whole different branch of science which is used to figure out what elements different things are made of just by seeing the light that comes from them! Learn more about that here.

Written By: Scott Alton
1People actually report lightning to be many different colors. In general, nearby lightning will have a purple glow due to the composition of the atmosphere, and the central part will look white simply because it is so overpoweringly bright and doesn’t give time for eyes to adjust. Most other colors that are reported are because the lightning is being viewed from a long ways off and the light has to travel through dust, rain, haze, pollution, or other things that can change its color.

How do Geysers Erupt to Over 300 Feet?

Note: This experiment shoots boiling water into the air, and should not be attempted at home without proper training and safety equipment!

Geysers are one of nature’s most incredible spectacles. In the most powerful eruptions, water can be shot over 300 feet–or the length of a football field–into the air!

Steam_Phase_eruption_of_Castle_geyser_with_double_rainbow

The Castle Geyser in Yellowstone National Park erupts. Water droplets in the air produce a picturesque rainbow against the blue sky. Photo credit: Brocken Inaglory

But just how do these things work? Geysers require some very specific conditions, which means that they only exist in certain locations. In fact, over half of the world’s geysers live in Yellowstone National Park. To find out why, let’s look at how one of these actually work!

When a geyser erupts, it is going through something known as a hydrothermal explosion, which sounds awesome, if a little complex. Luckily for us, the key to this is something familiar: boiling water. Even more fortunate, most of us have never seen a violent eruption of steam from the stovetop while cooking dinner.

The key to this is something called superheating. Most of us are familiar with the phases of matter. In everyday life, many of the things we see exist solely in a liquid, gaseous, or solid state. However, any material can be in any of these states depending on its heat and pressure. Below is the phase diagram for water. On the left is pressure which gets higher as we move up the diagram, and on the bottom is temperature, which increases as we move right.

Phase-Diagram-Water

Phase diagram for water. In geysers, high pressure can push water’s boiling temperature from 212℉ to almost 500℉, well above the temperature required to burn wood! Image from Pearson Education.

To make a geyser, we need to have superheated water, which simply means water that is boiling at higher than the normal boiling point. You can see on the diagram, increasing the pressure–moving up on the diagram from the normal boiling point–means that water stays in a liquid state until a higher temperature. Bingo! I think we just found out how geysers work!

 

Boiling

There is one more piece of the puzzle: How do we increase the pressure? By capping the boiling vessel, we don’t allow the air out. Capping the flask doesn’t instantly increase the pressure. Instead, as the water boils at the original pressure, liquid water turns into water vapor, which takes up about 1500 times as much space as in ts normal form. To fit in the fixed volume available to it (thanks to the cap) it has to become more tightly packed, which increases the boiling point slightly. This process repeats, causing the pressure to continue to rise and pushing the boiling point higher and higher!

As soon as the flask is open to the air again, we get our hydrothermal explosion: all of the compressed water vapor expands to its normal size flinging the surrounding water into the air, and water above the boiling point follows suit!

Water geyser 2

Why Is The Sky Blue?

Ever heard that the sky is blue because it’s reflecting Earth’s water? It’s a myth! If the sky was just mirroring the planet below, it would be brown in Utah. The real reason for our atmosphere’s hue has its roots in a more fundamental question: how do we see the world around us?

Spectrum

The electromagnetic spectrum. Credit: Florida Atlantic University

Human eyes are living light detectors. Color is just our brain’s code for incoming energy level. We call the most energetic light we can see “purple” and the least energetic “red”.

Our built-in biological cameras have a quirk: when confronted with a mixture of colors all at once, they’re overstimulated. Our eyes can’t resolve a blend of energy levels into individual signals, so our visual processing system defines a new category, which we call “white”. The sun’s radiation appears white before it reaches Earth, but it’s really a combination of many colors.

SunFromISS

The sun & Earth as seen from the ISS. Since sunlight hasn’t been scattered by the atmosphere on its way to the camera, it appears white. Credit: NASA

As white sunlight enters the atmosphere, the transition from empty space to air affects each of its components differently. Blue-violet light is bounced around the most drastically by air molecules in its path. From our perspective on Earth’s surface, scattered blue radiation fills the sky. Lower-energy light, which we interpret as the colors red through green, travels more directly downward to our eyes. We interpret this smaller combination — white minus blue-violet — as pale yellow.

Rayleigh-Scattering

Image courtesy of the City University of New York

As sunlight travels farther through the atmosphere, it’s more thoroughly scattered. At sunset, when rays travel sideways through a thick slice of air instead of straight down, we see more of the spectrum spread out across the sky. The leftover light traveling directly to us is mostly red and orange, which explains the sun’s ruddy appearance as it sets.

Screen Shot 2016-05-27 at 10.00.14 AM

Sunset from AstroCamp

Written By: Caela Barry

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