Let’s put leap years into perspective: since they only happen once every four years, the last time February 29 occurred on a Wednesday was 28 years ago, in 1984: nearly nine months before U.S. 1 published its first issue.
So this February 29, both a leap day and a U.S. 1 publication day, seemed as good a time as any to explore the history of leap years, the more recent issue of leap seconds, and the state of modern astronomy, the science that can explain it all.
And central New Jersey turns out to be a hot spot for astronomy thanks to the strong astrophysics program at Princeton University (think Lyman Spitzer and the Hubble Telescope), the State Planetarium, and the Amateur Astronomers Association of Princeton (AAAP).
The concept of leap years originated in the Roman Empire, explains Bill Murray, an astronomy lecturer at the State Planetarium in Trenton and a member of the AAAP. “For thousands of years, people have realized a year is 365 days long, but that’s not quite right.” Thanks to the work done by astronomers in Ancient Greece, Romans knew that the solar year –– the amount of time it takes the Earth to revolve around the sun –– was approximately 365.25 days. In Rome the calendar underwent a number of transformations, ultimately resulting in a 355-day calendar. To allow seasons to start and end on roughly the same days each year, however, the calendar relied on a periodic intercalary month called Mercedonius –– 22 days added to the year between February 22 and 23 or 23 and 24 –– to keep pace with the sun.
Had these intercalary months been added at the proper intervals, the Romans’ calendar would have remained decently accurate, at least in the short run. But the decision to add an intercalary month to a given year was made not by astronomers, but by the emperors themselves. And all too frequently, emperors were too busy fighting wars and political battles to worry about the number of days in the year.
Enter Julius Caesar, recently returned from a long but victorious battle in Egypt. The year was 46 B.C., and so many intercalary months had been skipped that it was difficult to even know what day it was. With the help of his astronomer, Sosigenes, Caesar arrived at a solution: add 10 days to the Roman calendar, and replace the problematic intercalary month with an intercalary day to occur between February and March every four years. After a 445-day year to recalibrate the calendar, the Julian calendar took effect. Three years would have 365 days, and one would have 366, for an average of 365.25 days per year. Perfect, right?
Not exactly. “After Caesar, over a span of 1,500 years more errors accumulated,” Murray explained. In 1582 Pope Gregory XIII realized that the calendar was once again well out of whack with the seasons when he observed that the seasons in which the church’s holidays occurred were slowly changing. Why? Because the solar year is approximately, but not exactly, 365.25 days long. It is, in fact, 365.2422 days long, and over the course of more than 1,600 years those 11 minutes and 14 seconds make a big difference.
The German astronomer Christopher Clavius was charged with revising the calendar. He introduced the Gregorian calendar – the one still in use today – which added a new twist into leap year calculations. Years divisible by 100 would not be leap years unless they were also divisible by 400. The new rule meant that the years 1600 and 2000 would be leap years, but 1700, 1800, and 1900 would not be. Problem solved, or so we thought.
Nearly 500 years later, scientists confronted a new problem. It was the mid-20th century, and computing as it is currently known was still in its infancy. Astronomers, meanwhile, observed that gravity and other forces were slowly but surely causing days to become longer, meaning that the Earth would take longer to make one complete rotation about its axis.
An astronomic day is also imprecise. Measured from different spots around the world, the length of a day will vary by a few milliseconds because of the Earth’s tendency to wobble on its axis.
Computing, on the other hand, requires a high level of precision. “The problem in the last 40 to 50 years is that we’re developing atomic clocks accurate to billionths of a second,” Murray explained. In the increasingly globalized world of the 1950s scientists realized they needed an exact measurement of what time it was to facilitate communications on an international scale. It needed to be exactly the same time in New York City and Miami; in Amsterdam and Paris.
This is where the concept of a leap second comes in. While atomic clocks rely on all days being identical in length, in astronomic time days are different lengths, which results in actual and astronomic time gradually drifting apart. To bridge this gap, an extra second is added to the end of June 30 or December 31 when the time difference approaches approximately 0.9 seconds. Since the first leap second in 1972, 25 have been added, with the most recent on December 31, 2008, and the next scheduled for one second before midnight on Saturday, June 30, 2012.
Adding an extra second is not as simple a solution as it seems. A computer cannot just know that it needs to add an extra second every once in a while. “Leap seconds are controversial because it makes havoc for IT people to update software,” Murray explained. “(A leap second) can’t be pre-programmed.” Leap seconds can complicate many complex and essential modern systems, including banking, navigation, and the internet.
There was a chance that the June, 2012, leap second would be the last. Because of the difficulties leap seconds present to IT professionals, a proposal to abolish leap seconds comes up for discussion every few years. Some –– like the United States, a strong supporter of abolishing leap seconds –– argue that leap seconds are more trouble than they’re worth. Others note the serious long-term consequences of letting actual time fall out of synch with astronomical time. Over the course of a lifetime, the time gap would amount to around a minute, but over the course of millennia what was once high noon could become the time the sun sets.
The decision is not in the hands of astronomers, but of the International Telecommunication Union (ITU), a United Nations agency responsible for coordinating worldwide radio and telecommunications. When the ITU convened earlier this year 700 officials representing about 70 countries again debated the merits of leap seconds and could not reach a consensus. The matter has now been shelved until a meeting in 2015.
With timekeeping firmly in the hands of IT professionals, astronomers –– the original timekeepers –– have found new questions to study. “Timekeeping is an ancient thing,” Murray says, “but it’s fairly minor now.” Astronomers today concern themselves with two extremes of time: the very beginning of the universe and its eventual fate.
“Go to Peyton Hall (the home of Princeton University’s astrophysics department) and you can talk to any number of people whose projects involve what was going on in the first trillionth of a second” after the universe was created, Murray says, as well as the universe’s fate billions of years from now.
Astronomers have more practical concerns, too. A February 19 New York Times article titled “For Space Mess, Scientists Seek Celestial Broom” examined the increasingly worrisome problem of space junk — out-of-use satellites and the like — that can wreak havoc by crashing into Earth or damaging the International Space Station or functional satellites. NASA workers are busy creating ways to safely destroy this orbiting litter.
That is what professional astronomers do. What about people for whom astronomy is mainly a hobby?
Says Murray: “I’ve been an amateur astronomer for about 40 years, and I started when I was 10 years old, so I’ve been doing this for a long time.”
The son of a lawyer and a homemaker, Murray grew up in New York and studied math and physics at Iona College. Astronomy has been an interest of his since childhood. “I was one of those children who grew up in the ’60s, so I was interested in the space race and moon landings, and that’s what triggered my interest in astronomy,” he says.
Murray has been an astronomy lecturer at the State Planetarium for 14 years. He moved to New Jersey in 1985 and began his career as an engineer at the Sarnoff Corporation (now SRI International) and then taught physics and math at Charter Tech High School in Somers Point, New Jersey.
Murray is also a member of the Amateur Astronomers Association of Princeton. The group hosts events throughout the year that are free and open to the public, but frequent attendees are encouraged to join AAAP for dues of $40 per year. The roughly 70 dues-paying members receive perks including access to AAAP’s newsletter and use of the United Astronomy Clubs of New Jersey’s observatory in Warren County, which offers better viewing conditions than observatories in the Princeton area because there is less light pollution.
The group brings in a guest speaker the second Tuesday of every month from September to June. The lecturers typically come from Princeton University or other nearby academic institutions. In the past year speakers have included the Institute for Advanced Study’s Freeman Dyson with a talk called “Regarding Extraterrestrial Life” and Princeton University’s Paul Steinhardt speaking on “Inflationary Cosmology on Trial.” Unless otherwise noted, lectures take place at 8 p.m. in Peyton Hall on the Princeton University campus.
The next lecture, scheduled for Tuesday, March 13, will be “Dark Matter” by Mark Trodden, professor of physics at the University of Pennsylvania. Other upcoming talks: Gregory Matloff of the New York City College of Technology on “Bisophere Extension” on April 10; and Mario Livio of the Space Telescope Science Institute on “The Latest Scientific Achievements of the Hubble Space Telescope” on May 8. Murray will give the final presentation of the academic year on June 12 at the State Planetarium.
AAAP also operates Simpson Observatory in the New Jersey part of Washington Crossing State Park. The observatory is open to the public, weather permitting, on Fridays beginning April 6 through October, from 8 to 11 p.m. AAAP members help visitors use the telescope and understand what they’re seeing.
Murray notes that AAAP also plans events around special astronomical occurrences. “Right now we’re planning for the transit of Venus across the face on the sun in June,” he said. The transit of Venus is similar to a solar eclipse, in which the moon passes between the sun and the earth and partially or fully blocks the sun. On Tuesday, June 5, Venus, which is slower-moving and four times the size of the moon, will pass in front of the sun, making the planet visible as a dark spot on the sun’s surface. (AAAP, incidentally, will not be the only group paying close attention to this event: Aram Friedman of Ansible Technologies will be creating a time lapse of the event. See sidebar, page 34.)
The transit of Venus is one of the rarest events in astronomy: it happened in 2004 for the first time since 1874 and 1882, and it won’t happen again until 2117 and 2125. A word to the wise: to watch the transit take the same precautions as you would during a solar eclipse and do not stare directly at the sun.
The final aspect of AAAP’s activities is public outreach. Many members own telescopes, which they bring to schools in an effort to get kids excited about astronomy. Even if a telescope doesn’t come to school, though, kids of all ages can gain hands-on experience with the stars at the State Planetarium, which has weekend programming for kids and adults that is free with museum admission. In the Planetarium’s 150-seat dome visitors can see up to 6,000 precisely projected stars from specially designed reclining seats.
“There is a sense of magic when someone enters the Planetarium,” says director Jay Schwartz. “The reclining seats, the inner dome, the star projector in the center of the room make you feel right away that you are in a special place.”
Kids as young as 2 years old can participate in One World, One Sky, at 1 p.m. on Saturdays and Sundays. During the program Sesame Street characters Big Bird and Elmo meet Elmo’s friend, Hu Hu Zhu, from China, and together they discover the sun, moon, and stars including Ursa Major (the Big Dipper) and Polaris (the North Star).
Children ages 3 to 10 can experience the Secret of the Cardboard Rocket at 2 p.m. They learn about the sun, Earth, and other planets as two young adventurers journey through the solar system in a homemade cardboard rocket.
Sea Monsters: A Prehistoric Adventure begins at 3 p.m. for ages 6 and up and features the giant creatures that lived underwater in the American Midwest of 80 million years ago. The real plesiosaurs and monosaurs are on view in the Planetarium’s main gallery as part of its Natural History Highlights exhibit.
At 4 p.m. Passport to the Universe, narrated by Tom Hanks, takes audiences of all ages on a journey of billions of light years to show how humans fit in among the planets, stars, and black holes that comprise the universe.
The Planetarium also joins forces with AAAP for sky observing sessions, with the next one scheduled for Friday, May 11, at 7:30 p.m. Attendees will start at the Planetarium with a short show, then head out to the Simpson Observatory to observe the night sky.
But visitors to the Planetarium come for more than the special programming. Even in an age of websites, iPhone apps, and other portable ways to see the stars, the Planetarium remains a resource for the astronomically curious. “Whenever someone gets a telescope, or even a new astronomy software program, they come to the Planetarium with questions,” Schwartz says.
Though Einstein would have you believe the cosmological constant was a term needed to account for a stationary universe, astronomers young and old know the true constant is the wonder and fascination created by the stars, the sun, and the planet we call Earth.
Amateur Astronomers Association of Princeton. Ludy D’Angelo, director. firstname.lastname@example.org. www.princetonastronomy.org.
New Jersey State Museum Planetarium, 205 West State Street, Trenton 08648. 609-292-6464. www.njstatemuseum.org. $7 adult; $5 child (12 and under). Group rates available. Open Tuesdays through Saturdays, 9 a.m. to 4:45 p.m., and Sundays, noon to 5 p.m.
Peyton Observatory, Peyton Hall, Princeton University campus. Public observation dates announced periodically. Visit www.astro.princeton.edu/observatory/publicobserving.php.