The Halloween Science FAQ

What is dry ice and how does it make that awesome fog?

Dry ice is the colorless, odorless, solid form of carbon dioxide, first reported in 1834 by the French chemist Charles Thilorier, who opened a container of liquid carbon dioxide needed for an experiment and observed that most of the liquid CO2 quickly evaporated, leaving a solid form on the bottom of the canister.

The surface temperature of dry ice is −109.3 °F. As it warms up, it sublimes, or transitions from the solid to gas form with no intermediate liquid form (a process called sublimation). These two characteristics make it an excellent coolant and since 1925, when solid CO2 was trademarked and sold as "Dry ice" by the DryIce Corporation of America, it's been used to flash freeze and refrigerate food and biological samples, make ice cream, bait mosquito traps (they're attracted to CO2) and make fog for theater productions, Sunn O))) concerts and haunted houses.

That fog is made by quickly changing the CO2 into its gas form. In an ice chest, dry ice sublimes at an average rate of 5-10 pounds every 24 hours. But placing dry ice in hot water accelerates sublimation considerably and turns the solid CO2 into CO2 gas. The cold CO2 gas meets the surrounding air and drops its temperature enough for condensation to occur and tiny droplets of water to form in the air and, voila, you have fog. Because carbon dioxide is heavier than air, and cold air is denser than warm air, the fog stays low to the ground for that extra creepy effect.

Why do we get goosebumps?

Goose bumps, also called goose flesh or goose pimples and known to medical professionals as cutis anserina ("cutis," skin + "anser," goose = goose skin) involuntarily develop on our skin when we become cold or experience strong emotions in a reflex called horripilation or piloerection. Whether we're freezing or getting the bejesus scared out of us, our sympathetic nervous systems pick up on a fight-or-flight situation and release adrenaline, muscles at the base of our body hairs contract, pull the hair erect, and create a shallow depression on the skin surface that causes the surrounding area to protrude. A goose bump is born.

In mammals with plenty of body hair or fur (chimps, otters, mice, cats, etc.), horripilation serves two purposes. One, erect hairs trap air, create insulation and aid heat retention. Two, erect hairs make an animal appear larger and helps intimidate enemies. In humans, horripilation as a response to cold or fear provides no known benefit since we lost most of our body hair some time ago.

What's the best candy container for trick-or-treating?

hwcandy_03What sort of container will provide you with maximum space for your candy haul? A bucket? A bag? The ol' pillow case? The guys (Guys? Gals? Robots? Not a whole lot of info available on who runs it.) at My Science Project conducted an experiment to find out.

First, the researchers accounted for the wide variety of candies available to the average trick-or-treater. They divided candy into three categories: ""˜premium' (fun-sized candy bars), "˜meh' (chewy boxed candies like Milk Duds), and "˜bottom of the barrel' (hard candy, gumballs, Dum Dum pops)," mixed roughly equal amounts by weight of top, middle, and bottom tier candies, and threw them into the containers by the handful, in order to give the candy a natural spatial distribution.

Each container was filled to a capacity where it could be reasonably carried without spilling and then weighed on a hanging spring scale (adjusted to account for the weight of the container).

Their results"¦

A 10-quart bucket held a total of 9.5 lbs of candy, consisting of 375 pieces.
A standard white 5-gallon plastic bucket allowed for 20 lbs of candy in 675 pieces.
A double-bagged, regular brown paper grocery bag held 25 lbs of candy, consisting of 885 pieces. The researchers found that the bag's unreliable handles were problematic once the bag was full.
A standard size pillow case, allowing enough empty room at the top so that it may be grasped and picked up with two hands, held a whopping 47.75 lbs of candy in the form of 1690 pieces.

Next, they wanted to know if it would be possible to even collect that much candy in one night of trick-or-treating. How far would one need to walk and how many houses would they have to hit?

The researchers picked two different middle-class residential areas representative of suburban America at large to use in the experiment. Campbell, California, in Silicon Valley is an older area with dense housing, and St. Peters, Missouri, a suburb of St. Charles, is more rural and contains many newer developments. The researchers used data from to approximate the number of houses per square mile and constructed several different trick-or-treating scenarios, varying the values for the number of candies received at each house, and the percentage of houses distributing candy. In their worst case scenario, they figure a trick-or-treater would have a 50% success rate and receive an average of 2.5 pieces of candy per house, while a decent trick-or-treating run would see a 75% success rate and 3.5 pieces of candy per house.

They researchers then used Google maps to work out what sort of mileage a candy hunter would have to clock. Assuming the first scenario, a trick-or-treater would have to visit approximately 1352 houses and cover .42 square miles in Campbell, given the housing density, to fill their pillowcase. Under the more favorable conditions of the second scenario, it would take visits to 644 houses and .2 square miles to fill a pillowcase. Looking at the their map, the researchers estimated roughly 1 linear mile of street distance per every .036 square miles, meaning one would walk about 11 miles to fill their candy bag in the worst case scenario.

In the better scenario in St. Peters, the lower density of housing necessitates that someone cover .6 square miles to fill a pillowcase. That's more walking than in the worst case scenario in Campbell—and since the researchers' housing densities are based on statistical averages and don't account for undeveloped land, a trick-or-treater would likely need to cover a lot more ground. [Image courtesy of They've got some fabulous stuff on their site. Who among us hasn't wondered whether Viagra keeps flowers fresh?]


Big Questions
Why Does Turkey Make You Tired?

Why do people have such a hard time staying awake after Thanksgiving dinner? Most people blame tryptophan, but that's not really the main culprit. And what is tryptophan, anyway?

Tryptophan is an amino acid that the body uses in the processes of making vitamin B3 and serotonin, a neurotransmitter that helps regulate sleep. It can't be produced by our bodies, so we need to get it through our diet. From which foods, exactly? Turkey, of course, but also other meats, chocolate, bananas, mangoes, dairy products, eggs, chickpeas, peanuts, and a slew of other foods. Some of these foods, like cheddar cheese, have more tryptophan per gram than turkey. Tryptophan doesn't have much of an impact unless it's taken on an empty stomach and in an amount larger than what we're getting from our drumstick. So why does turkey get the rap as a one-way ticket to a nap?

The urge to snooze is more the fault of the average Thanksgiving meal and all the food and booze that go with it. Here are a few things that play into the nap factor:

Fats: That turkey skin is delicious, but fats take a lot of energy to digest, so the body redirects blood to the digestive system. Reduced blood flow in the rest of the body means reduced energy.

Alcohol: What Homer Simpson called the cause of—and solution to—all of life's problems is also a central nervous system depressant.

Overeating: Same deal as fats. It takes a lot of energy to digest a big feast (the average Thanksgiving meal contains 3000 calories and 229 grams of fat), so blood is sent to the digestive process system, leaving the brain a little tired.

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

More Details Emerge About 'Oumuamua, Earth's First-Recorded Interstellar Visitor

In October, scientists using the University of Hawaii's Pan-STARRS 1 telescope sighted something extraordinary: Earth's first confirmed interstellar visitor. Originally called A/2017 U1, the once-mysterious object has a new name—'Oumuamua, according to Scientific American—and researchers continue to learn more about its physical properties. Now, a team from the University of Hawaii's Institute of Astronomy has published a detailed report of what they know so far in Nature.

Fittingly, "'Oumuamua" is Hawaiian for "a messenger from afar arriving first." 'Oumuamua's astronomical designation is 1I/2017 U1. The "I" in 1I/2017 stands for "interstellar." Until now, objects similar to 'Oumuamua were always given "C" and "A" names, which stand for either comet or asteroid. New observations have researchers concluding that 'Oumuamua is unusual for more than its far-flung origins.

It's a cigar-shaped object 10 times longer than it is wide, stretching to a half-mile long. It's also reddish in color, and is similar in some ways to some asteroids in own solar system, the BBC reports. But it's much faster, zipping through our system, and has a totally different orbit from any of those objects.

After initial indecision about whether the object was a comet or an asteroid, the researchers now believe it's an asteroid. Long ago, it might have hurtled from an unknown star system into our own.

'Oumuamua may provide astronomers with new insights into how stars and planets form. The 750,000 asteroids we know of are leftovers from the formation of our solar system, trapped by the Sun's gravity. But what if, billions of years ago, other objects escaped? 'Oumuamua shows us that it's possible; perhaps there are bits and pieces from the early years of our solar system currently visiting other stars.

The researchers say it's surprising that 'Oumuamua is an asteroid instead of a comet, given that in the Oort Cloud—an icy bubble of debris thought to surround our solar system—comets are predicted to outnumber asteroids 200 to 1 and perhaps even as high as 10,000 to 1. If our own solar system is any indication, it's more likely that a comet would take off before an asteroid would.

So where did 'Oumuamua come from? That's still unknown. It's possible it could've been bumped into our realm by a close encounter with a planet—either a smaller, nearby one, or a larger, farther one. If that's the case, the planet remains to be discovered. They believe it's more likely that 'Oumuamua was ejected from a young stellar system, location unknown. And yet, they write, "the possibility that 'Oumuamua has been orbiting the galaxy for billions of years cannot be ruled out."

As for where it's headed, The Atlantic's Marina Koren notes, "It will pass the orbit of Jupiter next May, then Neptune in 2022, and Pluto in 2024. By 2025, it will coast beyond the outer edge of the Kuiper Belt, a field of icy and rocky objects."

Last week, University of Wisconsin–Madison astronomer Ralf Kotulla and scientists from UCLA and the National Optical Astronomy Observatory (NOAO) used the WIYN Telescope on Kitt Peak, Arizona, to take some of the first pictures of 'Oumuamua. You can check them out below.

Images of an interloper from beyond the solar system — an asteroid or a comet — were captured on Oct. 27 by the 3.5-meter WIYN Telescope on Kitt Peak, Ariz.
Images of 'Oumuamua—an asteroid or a comet—were captured on October 27.

U1 spotted whizzing through the Solar System in images taken with the WIYN telescope. The faint streaks are background stars. The green circles highlight the position of U1 in each image. In these images U1 is about 10 million times fainter than the faint
The green circles highlight the position of U1 in each image against faint streaks of background stars. In these images, U1 is about 10 million times fainter than the faintest visible stars.
R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Color image of U1, compiled from observations taken through filters centered at 4750A, 6250A, and 7500A.
Color image of U1.
R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Editor's note: This story has been updated.


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