Who came up with leap seconds and why do we have them?

Planet Earth five minutes before midnight. (Photo: Stefan Puetz/Corbis)

It is going to be a long day at least by cosmic standards.

Tuesday will be one full second longer thanks to the complex science that led to the creation of the "leap second." You've probably heard a lot about the leap second today, and seen it trending on social media.

So what is it and why do we have it? The extra second is added to calibrate time to accommodate for a slowdown of the Earth's rotation as a result of winds, tides and motions of the Earth's inner, fluid core, said Dr. Thomas Herring, professor of geophysics at the Massachusetts Institute of Technology.

There is nothing new about humans manipulating the perception of time. For centuries, humans have adopted calendars in attempts to maximize the day. Unlike leap year, however, the leap second is far less familiar and might leave you asking, "Who comes up with this stuff?"

The International Earth Rotation and Reference Systems Service (IERS) is the body in charge of adding leap seconds. In 1987 the International Astronomical Union and the International Union of Geodesy and Geophysics formed the IERS. Since that time, the IERS has been the authority on leap seconds. The last leap second was added on June 30, 2012.

According to Herring, who is also the analysis coordinator for the IERS, the leap second fills in the disparity between atomic time, or Coordinated Universal Time (UTC)*, and solar time, or Universal Time (UT1). The objective of the leap second is to keep these two distinct "clocks" in alignment.

Unlike leap year, which is based on the orbit of the Earth around the sun, the leap second is based on the rotation of the Earth, which according to Herring is far less stable.

Herring says it is his job to oversee how the organization can "better monitor how the Earth's rotation varies over time" and thus affects the way time is recorded. Herring explained that Tuesday's UT1 is 0.67614 seconds behind UTC. After the second is added, the UT1 will be 0.3 seconds ahead. Once UT1 again falls behind by more than 0.5 seconds, the IERS will determine when the next second should be added (it's projected to be either Dec. 31 or June 30).

Do we really need an extra second?

There is a growing push to stop implementing the second. According to Herring, the leap second has "much more potential to cause disruption." Herring says he supports ending the use of the leap second. He said when the second is added later today, in parts of the world, financial institutions will be open and it may adversely affect their calendars. He also cited the amount of software (such as Apple products) that is based off of atomic time and hasn't been built to account for the added seconds as a reason to stop using the leap second.

Herring said there is a community of scientists in astronomy and related fields who argue that the use of the leap second is needed for their calculations. Those who fall on this side of the argument say that getting rid of the second would cause a greater disparity over time and ultimately cause damage.

According to Herring, those for discontinuing the use of the second base their opinions off of the assumption that "atomic time will remain within half a second of time given by the rotation of the Earth."

*Time based on the coordinated calculations of atomic clocks in countries around the world. Atomic clocks are based on the oscillation of the cesium-133 atom.