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How Do Fireworks Get Their Colors?

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It’s all about chemistry. Inside an “aerial shell” firework that gets launched into the sky, there’s a “bursting charge,” black powder (aka gunpowder) or a black powder substitute and a bunch of small pellets called “pyrotechnic stars.” The stars are made up of a fuel, an oxidizer, a finely ground metal or metal salt powder, and a binder to hold the ingredients together. 

When a firework explodes mid-air thanks to the bursting charge and the black powder, the gas and the heat that are produced ignite the stars. The atoms of the metal powders in the stars absorb that heat energy and their electrons rearrange from their lower-energy ground state to a higher-energy “excited” state. As they come back down to their ground state, the excess energy is emitted as light. 

The energy difference between the excited and ground states of the electrons is different for each of the chemical powders used in the stars, and the amount of energy emitted determines what wavelength of light they’ll produce and the color we see. That means that the different types of metals used in the stars each have a characteristic color. 

Here are some of the metals and specific compounds that are typically used in fireworks to produce different colors:

Red: strontium (strontium carbonate, SrCO3), for intense reds and lithium (lithium carbonate, Li2CO3, or lithium chloride, LiCl) for medium reds

Orange: calcium (calcium chloride, CaCl2)

Yellow: sodium (sodium nitrate, NaNO3)

Green: barium + chlorine producer (barium chloride, BaCl2)

Blue: copper + chlorine producer (copper chloride, CuCl2)

Purple: strontium + copper compounds

Gold: charcoal, iron, lampback

White/Silver: titanium, aluminum, magnesium, beryllium

For more on the science of fireworks, check out this video by the American Chemical Society:

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
What Are the Northern Lights?
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Over the centuries, many have gazed up at one of the Earth’s most fascinatingly beautiful natural wonders: the Northern Lights. In the past couple of weeks, some lucky American stargazers have gotten the chance to see them from their very own backyards—and could again this week, according to Thrillist. But what are they?

Before science was able to get a read on what exactly was happening in the night sky, ancient tribes had their own theories for what caused the jaw-dropping light show. Many early beliefs had roots in religion, such as that the light was a pathway souls traveled to reach heaven (Eskimo tribes) or that the light was an eternal battle of dead warriors (Middle-Age Europe). Early researchers were a bit more reasonable in their approximations, and most surrounded the idea of the reflection of sunlight off the ice caps. In 1619, Galileo Galilei named the lights the aurora borealis after Aurora, the Roman goddess of morning, after concluding they were a product of sunlight reflecting from the atmosphere.

Today, scientists have come to the general agreement that the lights are caused by the collision of electrically charged solar particles and atoms from our atmosphere. The energy from the collisions is released as light, and the reason it happens around the poles is because that's where the Earth’s magnetic field is the strongest. In 2008, a team at UCLA concluded that “when two magnetic field lines come close together due to the storage of energy from the sun, a critical limit is reached and the magnetic field lines reconnect, causing magnetic energy to be transformed into kinetic energy and heat. Energy is released, and the plasma is accelerated, producing accelerated electrons.”

"Our data show clearly and for the first time that magnetic reconnection is the trigger," said Vassilis Angelopoulos, a UCLA professor of Earth and Space Sciences. "Reconnection results in a slingshot acceleration of waves and plasma along magnetic field lines, lighting up the aurora underneath even before the near-Earth space has had a chance to respond. We are providing the evidence that this is happening."

The best time to see the Northern Lights is during the winter, due to the Earth’s position in relation to the sun (shorter days means darker night skies). And by the way, it’s not just the North Pole that puts on a show—there are Southern Lights, too. There are also aurora borealis on other planets—including Mars—so rest assured that future generations born “abroad” will not miss out on this spectacular feat of nature.

Haven’t seen them yet? Traditionally, the best places to catch a glimpse of the Northern Lights are in Iceland, Sweden, Norway, Finland, Greenland, northern Canada, and Alaska. Maybe you'll get lucky this week and sneak a peek from your very own window. Check out Aurorasaurus for regular updates on where they are showing.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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