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The Position of the Moon Slightly Affects the Rainfall on Earth

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We like to give the moon credit for all kinds of weird things, from werewolves and hockey fights to the ocean’s shifting tides (though only the latter is true). And now the Moon can add a new accomplishment to its resume: messing with our rainfall. A paper published last week in Geophysical Research Letters shows that the position of the Moon slightly affects the amount of rain we get here on Earth.

The Sun, the Moon, and the Earth are all constantly in motion, both orbiting and revolving. Each of these bodies has its own gravitational field, and we are affected by all of them. The Sun’s gravity is what keeps us on track in our path around the solar system. But the Moon, being so very tiny by comparison, can’t do anything quite that big. Instead, when the Moon is high in the sky, its gravitational field just kind of tugs on our planet. This tug is not enough to move Earth out of its path, but it is enough to give us what amounts to a little squeeze. The part of the planet directly under the Moon bulges a little bit, swelling upward. When this happens over the ocean, we call it high tide.

The same gravitational pull is responsible for changes in Earth’s rainfall, says study co-author Tsubasa Kohyama. While researching changes in atmospheric pressure, Kohyama noticed a strange, consistent pattern.

Since the 1800s, scientists have been suggesting that the Moon’s place in the sky can impact air pressure on Earth. After analyzing 15 years of rainfall data collected by NASA and the Japan Aerospace Exploration Agency's Tropical Rainfall Measuring Mission satellite, Kohyama and his co-author John Wallace were able to confirm that those air pressure changes translate to changes in rainfall.

“When the Moon is overhead or underfoot, the air pressure is higher," Kohyama said in a press statement. It goes back to that bulge. The wedge of Earth underneath the Moon at any given moment also includes the atmosphere above it, and under high gravitational pressure, that atmosphere swells, too. High pressure raises the temperature of the swelling pocket of air, which then retains more moisture. But the same air parcels are now farther from their moisture capacity, the researchers said.

"It's like the container becomes larger at higher pressure," Kohyama said. The relative humidity affects rain, he said, because "lower humidity is less favorable for precipitation."

As a result, when the Moon is high, the rain is slightly lighter. When the moon is on the horizon, or rising, there's a little more rain. But the change is so small that you'll never notice it; the researchers estimated the lunar influence at about 1 percent. "No one should carry an umbrella just because the Moon is rising," Kohyama said. While these findings may not be of much use for the daily forecast, the authors hope their findings can help scientists fine-tune their climate models.

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Today's Wine Glasses Are Almost Seven Times Larger Than They Were in 1700
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Holiday party season (a.k.a. hangover season) is in full swing. While you likely have no one to blame but yourself for drinking that second (or third) pour at the office soiree, your glassware isn't doing you any favors—especially if you live in the UK. Vino vessels in England are nearly seven times larger today than they were in 1700, according to a new study spotted by Live Science. These findings were recently published in the English medical journal The BMJ.

Researchers at the University of Cambridge measured more than 400 wineglasses from the past three centuries to gauge whether glass size affects how much we drink. They dug deep into the history of parties past, perusing both the collections of the Ashmolean Museum of Art and Archaeology at the University of Oxford and the Royal Household's assemblage of glassware (a new set is commissioned for each monarch). They also scoured a vintage catalog, a modern department store, and eBay for examples.

After measuring these cups, researchers concluded that the average wineglass in 1700 held just 2.2 fluid ounces. For comparison's sake, that's the size of a double shot at a bar. Glasses today hold an average of 15.2 fluid ounces, even though a standard single serving size of wine is just 5 ounces.

BMJ infographic detailing increases in wine glass size from 1700 to 2017
BMJ Publishing group Ltd.

Advances in technology and manufacturing are partly to blame for this increase, as is the wine industry. Marketing campaigns promoted the beverage as it increasingly became more affordable and available for purchase, which in turn prompted aficionados to opt for larger pours. Perhaps not surprisingly, this bigger-is-better mindset was also compounded by American drinking habits: Extra-large wineglasses became popular in the U.S. in the 1990s, prompting overseas manufacturers to follow suit.

Wine consumption in both England and America has risen dramatically since the 1960s [PDF]. Cambridge researchers noted that their study doesn't necessarily prove that the rise of super-sized glassware has led to this increase. But their findings do fit a larger trend: previous studies have found that larger plate size can increase food consumption. This might be because they skew our sense of perception, making us think we're consuming less than we actually are. And in the case of wine, in particular, oversized glasses could also heighten our sensory enjoyment, as they might release more of the drink's aroma.

“We cannot infer that the increase in glass size and the rise in wine consumption in England are causally linked,” the study's authors wrote. “Nor can we infer that reducing glass size would cut drinking. Our observation of increasing size does, however, draw attention to wine glass size as an area to investigate further in the context of population health.”

[h/t Live Science]

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Researchers Pore Over the Physics Behind the Layered Latte
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The layered latte isn't the most widely known espresso drink on coffee-shop menus, but it is a scientific curiosity. Instead of a traditional latte, where steamed milk is poured into a shot (or several) of espresso, the layered latte is made by pouring the espresso into a glass of hot milk. The result is an Instagram-friendly drink that features a gradient of milky coffee colors from pure white on the bottom to dark brown on the top. The effect is odd enough that Princeton University researchers decided to explore the fluid dynamics that make it happen, as The New York Times reports.

In a new study in Nature Communications, Princeton engineering professor Howard Stone and his team explore just what creates the distinct horizontal layers pattern of layered latte. To find out, they injected warm, dyed water into a tank filled with warm salt water, mimicking the process of pouring low-density espresso into higher-density steamed milk.

Four different images of a latte forming layers over time
Xue et al., Nature Communications (2017)

According to the study, the layered look of the latte forms over the course of minutes, and can last for "tens of minutes, or even several hours" if the drink isn't stirred. When the espresso-like dyed water was injected into the salt brine, the downward jet of the dyed water floated up to the top of the tank, because the buoyant force of the low-density liquid encountering the higher-density brine forced it upward. The layers become more visible when the hot drink cools down.

The New York Times explains it succinctly:

When the liquids try to mix, layered patterns form as gradients in temperature cause a portion of the liquid to heat up, become lighter and rise, while another, denser portion sinks. This gives rise to convection cells that trap mixtures of similar densities within layers.

This structure can withstand gentle movement, such as a light stirring or sipping, and can stay stable for as long as a day or more. The layers don't disappear until the liquids cool down to room temperature.

But before you go trying to experiment with layering your own lattes, know that it can be trickier than the study—which refers to the process as "haphazardly pouring espresso into a glass of warm milk"—makes it sound. You may need to experiment several times with the speed and height of your pour and the ratio of espresso to milk before you get the look just right.

[h/t The New York Times]

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