How Do They Dye the Chicago River Green for St. Patrick's Day?


It wouldn’t be a St. Patrick’s Day celebration in the Windy City without 400,000 spectators crowding the banks of the Chicago River to “ooh” and “aah” at its (temporarily) emerald green tinge. But how do officials turn the water green?

First, a bit of history: The dyeing tradition became an annual thing nearly 60 years ago, in 1962, but its real origins go back even further. In the early days of his administration as Mayor of Chicago, Richard J. Daley was a man on a mission to develop the city’s riverfront area. There was just one problem: The river itself was a sewage-filled eyesore. In order to get to the bottom of the city’s pollution problem and pinpoint the exact places where waste was being discarded into the waterway (and by whom), Daley authorized the pouring of a special green dye into the river that would allow them to see exactly where dumping was occurring.

Fast-forward to late 1961 when Stephen Bailey—part of the Chicago Journeymen Plumbers Local, the city’s St. Patrick’s Day Parade chairman, and a childhood friend of Daley’s—witnessed a colleague’s green-soaked coveralls following a day of pouring Daley’s dye into the Chicago River. That gave Bailey an idea: If they could streak the Chicago River green, why not turn it all green?

Three months later, revelers got their first look at an Ecto Cooler-colored river when the city poured 100 pounds of the chemical into the water. They got a really good look, too, as the river remained green for an entire week.

Over the next several years, the same practice was repeated, and again it was carried out by the Plumbers Local. The only difference was that the amount of dye used was cut in half over the next two years until they finally arrived at the magic number: 25 pounds of dye = one day of green water.

Unfortunately, the dye that was intended to help spot pollution was an oil-based fluorescein that many environmentalists warned was actually damaging the river even more. After fierce lobbying, eco-minded heads prevailed, and in 1966 the parade organizers began using a powdered, vegetable-based dye.

While the exact formula for the orange powder (yes, it's orange until it's mixed with water) is kept top-secret—in 2003 one of the parade organizers told a reporter that revealing the formula would be akin to “telling where the leprechaun hides its gold”—there are plenty of details that the committee lets even non-leprechauns in on.

The dyeing process will begin at 9 a.m. on the morning of the parade—which this year is Saturday, March 16 (it's always held on a Saturday) when six members of the local Plumbers Union hop aboard two boats, four of them on the larger vessel, the remaining two on a smaller boat.

The larger boat heads out onto the water first, with three members of the crew using flour sifters to spread the dye into the river. The smaller boat follows closely behind in order to help disperse the substance. (The best place to catch a glimpse is from the east side of Michigan Avenue, or on Upper and Lower Wacker Drive between Michigan Avenue and Columbus Drive.)

Approximately 45 minutes later, voila, the Chicago River is green—but don’t expect it to stay that way. These days, the color only sticks around for about five hours. Which is roughly the same amount of time it takes to get a perfectly poured pint of Guinness if you venture out to an Irish pub on St. Patrick’s Day.

A version of this article first ran in 2017.

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If the Moon is Gradually Moving Farther Away From Us, Will Its Gravitational Pull Ever Cease on Earth?

Robert Frost:

The Moon is receding from the Earth, but will not continue to do so forever. We have to consider why the Moon is moving away at around 1.5 inches (3.78 cm) per year—a force is necessary to cause that.

The Moon exerts a tidal force on the Earth, causing a bulge. But, because the Earth rotates, that bulge is not directly between the Earth and Moon. It is slightly in front. That bulge has a gravitational pull on the Moon, causing it to move forward, slightly faster.

Causing the Moon to move slightly faster results in it climbing very slowly to a higher orbit. The Moon climbs higher by about 3.78 cm per year. But, since we just said that the force is gravitational and we know that gravity decreases with distance, we know that the force will also decrease with distance.

That means the rate at which the Moon recedes will decrease with time. But there's more to it than that. A force acts upon both bodies. While the impact on the Moon is causing it to recede, the impact on the Earth is that it is being caused to slow its rotation. The day is getting longer.

Eventually, the length of the day will match the orbital period of the Moon. That means both bodies will be tidally locked—meaning the same part of the Earth will always face the same part of the Moon. And if that happens, there is no longer a leading bulge and thus no longer a force causing the Moon to move away.

This would happen when the orbital period of the Moon is about 47 days. That would put the Moon at a distance of about 550,000 km; less than half as far again as it is today. In other words, not very far.

However, it will take a long time for that to happen. In the meantime, the Sun will turn into a red giant and its outer layers will extend to where Mars is today, meaning Earth, the Moon, and every In-N-Out restaurant will have been swallowed up and turned into loose atoms.

This post originally appeared on Quora. Click here to view.

What Makes Dogs Tilt Their Heads?

By tilting its head slightly to the side, a dog can melt the heart of even the most hardened cat person. Most everyone finds this behavior adorable, but few people can explain what compels a dog to do it. Are dogs somehow aware of the effect they have on humans, using a cute trick to exploit us for affection?

Experts say the real answer has more to do with your dog's ability to empathize. Dogs are impressively good at reading and responding to our body language and vocal cues. When you're lecturing your pooch for taking food off the counter, they're taking it all in even if the literal message gets lost in translation. Same goes for when you’re giving your pup praise. Dogs are capable of recognizing certain parts of human language, so when they cock their heads as you speak to them, it's possible they're listening for specific words and inflections they associate with fun activities like meals and playtime.


The head-tilt may also have something to do with how the canine ear is constructed. Even though dogs sense frequencies humans are incapable of hearing, their ability to detect the source of sounds is less precise than ours. A dog's brain calculates extremely minuscule differences between the time it takes a sound to reach each ear, so a simple change in head position could provide them with useful sensory information. When dogs tilt their heads, some experts believe they are adjusting their pinnae, or outer ears, in order to better pinpoint the location of a noise.

Stanley Coren of Psychology Today believes that vision also has something to do with this behavior. If you try holding your fist in front of your nose, you can get a fair sense of what it’s like to view the world with a muzzle. When watching someone speak, the "muzzle" will block the lower part of their face from view, and if you tilt your head to one side you will be able to see it more clearly. In addition to being able to perceive emotional cues in our voices, dog can also read our facial expressions. When cocking their heads to the side, Coren suggests that dogs are trying to get a better view of our mouths, where our most expressive facial cues originate.

If your dog is a frequent head-tilter, this could mean that they're especially empathetic. Some experts have reported that dogs who are more socially apprehensive are less likely to tilt their heads when spoken to. But if your dog doesn't display this behavior, there's no need to automatically label them as a canine sociopath (especially if they have pointy ears or a flatter snout). And even if the head tilt does come from instinct, the more owners respond to it with positive reinforcement, the more likely dogs are to do it in search of praise.

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