Featured Post from Villanova University

Leap Years and the Connection Between Astronomy and Our Lives

Feb 23, 2024

5 min

Most of us know February 29 as a whimsical anomaly—nothing more than a chance to tease our friends or colleagues born on this day as technically being a quarter of their purported age.


But how often do we think about the origins of the day as we now know it? Or about the near-universal implementation of this specific way to keep track of time? Do we ever consider the impact a leap year could have on everyday life?


Frank Maloney, PhD, an associate professor of astronomy and astrophysics at Villanova University, has been teaching for nearly 12 leap years (47 years). He is an expert in timekeeping and calendaring, calling them a “fundamental connection to our lives, ruled by the motion of objects in the sky,” because “everyone has to agree what day and time it is.”


Dr. Maloney currently teaches a course called “Earth: Our Habitable World,” where he discusses this and other connections between astronomy and people’s lives.


In the case of leap years, the astronomical phenomenon from which they originate—the Earth’s time to orbit the sun—is a very important one to accurately track.


“You want your calendar to keep pace with the seasons,” Dr. Maloney explained. “There are all sorts of ways of measuring the pace of the Earth around the sun, but the way that [also] keeps pace with seasons is called the tropical year, and unfortunately, there’s not an integer number of days in that year. We can’t ignore it, because after the first year you’re off by a quarter of a day and after four years off by a full day, and so on.”


Ancient civilizations were aware there were slightly more than 365 days in a solar year but didn’t know exactly how much more. Gradually, the seasons would become unsynchronized with the calendar, and those various civilizations added days back in at random times to realign.


“In those days, it might be possible to leave one area in April, and arrive [somewhere else] the previous December,” Dr. Maloney joked.


The concept of a leap year began with the Roman Empire’s implementation of Julius Caesar’s namesake calendar on January 1, 45 B.C.E., at his behest. The Julian calendar was a solar calendar, which consisted of a 365-day year, and a 366-day leap year every four years, without exception. It was often added as a duplicate day in the middle of February.


“But a year is not exactly 365 and a quarter days. It’s a little bit less,” Dr. Maloney explained. “By the Middle Ages, it was 10 or so days out of whack with the tropical year. Astronomers would have seen that very easily... but the reason to change it was not there.”


Not until the late 16th century, that is. And the reason it did change was because Easter had moved out of line with the vernal equinox.


“Nearly all calendars have a mystical, religious or theological component,” Dr. Maloney said. “In the Roman Church, Easter is reckoned as the first Sunday after the first full moon on or after the vernal equinox, or first day of spring.”


In order to have Easter fall back in line with the equinox, Pope Gregory XIII issued a papal bull in 1582, which declared a year to be a more accurate 365 days, 5 hours and 49 minutes in length (roughly).


What that meant for leap years was that, instead of every four years without exception, they would now occur every four years except on century marks, unless that century mark was divisible by 400. For example, 1900 was not a leap year, but 2000 was. The years 2100, 2200 and 2300 will not be leap years.


The global switch to a new calendar was not easy or done in haste. To enact the initial calendar change, 1582 went from October 4 to October 15 to eliminate extra accumulated days. Catholic countries mostly followed suit soon after, but many others resisted, as citizens feared it was a political trick. It took centuries to get to the near-universal use of the Gregorian calendar we have today.


Great Britain and other Commonwealth nations did not adopt the Gregorian calendar until 1752. An individual such as George Washington could have been considered to be born on one day in the Julian calendar and have a different birthday in the Gregorian calendar. In the American colonies, September 1752 skipped to the 14th day of the month from the second.


The most recent country to switch from the Julian to Gregorian calendar was Greece in 1923. By then, the calendar was roughly two weeks off from the tropical year. In the early 1900s, when globalization was commencing, this was a big deal.


“You could get in an airplane and fly someplace, and not even know what day you’d be landing. According to the calendar, it’d be time travel,” Dr. Maloney said.


Saudi Arabia still used a few elements of the Islamic calendar for fiscal purposes until 2016, and Afghanistan, Iran, Nepal and Ethiopia are the only countries in the world that do not officially use the Gregorian calendar currently.


So, what does all this mean for people today? For starters, historians and genealogists must be careful when studying historical dates and events. For example, a country may have still been using the Julian calendar during a particular time period, or perhaps an event might have occurred during the time days were skipped to make the switch from the Julian to the Gregorian calendars.


“If an infant were born [in the American colonies] on the second of September 1752, for example, and died on the 14th, they were not really 12 days old,” Dr. Maloney said. “Or if a war began in a country one day but started on a different day in a different country, it causes confusion.”


Leap years and other adjustments to timekeeping can also cause a plethora of computing and software issues, impacting multiple industries. This is especially true in the digital age where time-stamping is so ubiquitous. Case in point, on occasion, we actually have to add a leap second to time to account for the slowing of Earth’s rotation. These leap seconds are added after 11:59:59 on either December 31 or June 30, when needed.


“There’s a great deal of controversy about this particular practice,” Dr. Maloney said. “It really confounds software. A jet airplane, for example, can travel a fairly long distance in one second. Time has to be kept now to fractions of seconds, [even for things like] lawsuits and insurance policies. Timekeeping is a very important task for astronomers.”


It seems those astronomers have it figured out... for now. Even the Gregorian calendar will eventually need an adjustment, as its margin of error is about 27 seconds per year. That means every 3,236 years—so sometime in the early 4800s—an additional extra day will need to be added somewhere to correct it.


Luckily, we have some time to plan ahead.


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3 min

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5 min

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Steve Goldsmith: In 2022, we published a paper showing that salt—sodium in particular—is seeping into Philadelphia's water supply, and it's timed with snow melts. We found that if you drank a glass of tap water during the peak period in the winter of 2018-19, your sodium intake would be six times what the Environmental Protection Agency (EPA) recommends within a glass of water for someone on a low-sodium diet. We are susceptible in this region because most of our water supply comes from rivers, and the rivers receive that salt runoff. Some of our findings indicate this is a chronic issue and not limited to winter months. All that contaminated shallow groundwater causes the concentration to rise year-round, even in the summer. In a recent paper, we discuss the issue of salt that lands on the side of the road. When it does, it infiltrates into soil, and then it goes into shallow groundwater before entering our streams. Oftentimes when salt is applied to the road and you receive that initial precipitation, you are left with runoff with salinity near the concentration of sea water, which is very bad for freshwater organisms. PR: Have those studies found other impacts beyond those created directly by sodium? SG: It’s certainly not just a sodium issue—it's also a chloride issue. Chloride does have a negative impact on aquatic organisms, but it can also corrode drinking water infrastructure. If you have lead pipes in that infrastructure, that can lead to a range of human health issues. Even just to prevent those problems, applying chemicals to protect from the corrosion of pipes increases costs. Perhaps the worst part is when road salt infiltrates shallow soil and groundwater, the sodium is left behind preferentially in soils because it's displacing other positively charged elements, which could then go into groundwater. The elements it replaces are metals. If we have more salt runoff on the side of the roads, chances are, if we look in those streams, we are going to see higher concentrations of heavy metals like copper, zinc and even lead. PR: You have mentioned the efficacy of brine. What is brine and why is it more effective than traditional road salt? SG: If you’ve ever driven behind a rock salt truck, you probably noticed it pelts your windshield and shoots salt everywhere. A lot of that rock salt ends up following the natural trajectory of the road, which is designed to drain towards the sides to keep water from pooling. As soon as a snowstorm happens, it's going to melt and flow into the storm drain. That, of course, is bad for the environment, but also doesn’t help remove ice from the road. With brine, the application is a diluted road salt with water mixture that is usually about 23 percent sodium chloride by volume, and it’s referred to as an “anti-icing” measure. The saltwater infiltrates the top layer of pavement and embeds in the roadway itself, which keeps ice from crystallizing when snow or water hits the surface. To use an analogy, let’s say you have a large rock that you placed on top of the pavement, but you also have a quarter of that rock’s volume in sand. If you put that sand onto the pavement, it will permeate into nooks and crannies. That's the same idea here: use less material and in a way that makes it stick better to the surface and reduces the need to reapply as often during and after storms. PR: What are potential positive impacts if municipalities switch from road salt to brine? SG: There are limited studies on this, but it's been shown that if done properly, brining can reduce salt runoff into streams by anywhere from 23 to 40 percent. If it's 40 percent, you have almost cut the problem in half, and that lower peak salt concentration and runoff would have a profound positive impact on aquatic organisms that are downstream. From a cost standpoint—and I say this theoretically because there are other up-front costs associated with brining at the municipal level—if you reduce salt concentrations by up to 40 percent it means you apply a lot less and therefore spend a lot less. PR: What can individuals do to decrease road salt runoff, and how much of an impact does individual use have? SG: We can start by addressing the household salt application problem. Another one of our recent papers suggests that other impervious surfaces, like driveways, sidewalks and parking lots, are probably contributing even more than the roadway application. The best estimate is that individual or private contractor use could be over 10 times what you see on roads. For researchers, part of addressing this is trying to understand why people apply so much salt on their personal properties: are they afraid of lawsuits? Keeping with the Joneses? Are they not aware of ordinances that say you have to shovel within a certain number of hours, which would negate the need for salt anyway? For homeowners and other individuals, one proposed solution is to use a coffee mug’s worth of salt for every 10 sidewalk squares. Think of it as a “low-sodium diet” to make sure you’re not overapplying. It’s a way we can limit our use of salt and do so in a way that doesn't jeopardize safety. These individuals can also sweep up salt applied before a storm that never materialized to use before the next one. This will prevent the possibility of rain needlessly dissolving the salt. PR: Are there effective alternatives to road salt that individuals can use? SG: The only truly effective alternative, unfortunately, is simply using less road salt. While some people apply sand, it also washes into local streams, causing environmental harm. Another option that has gained attention is beet juice—what I like to call the “Dwight Schrute” solution. Beet juice actually works better than road salt because its organic acids prevent ice from crystallizing at temperatures much lower than those at which rock salt is effective. However, from an environmental standpoint, beet juice contains high levels of nutrients, which can contribute to algae growth if it enters waterways. Additionally, recent studies suggest it may also be toxic to aquatic organisms. The growing consensus is that while some road salt is necessary, we need to use less of it.

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