2021 will be the shortest year in decades - this is why

Believe it or not, this year is set to be shorter than normal, due to the fact that the Earth is moving faster than it ever has in the last 50 years.

The speed of the Earth’s rotation can be affected by a number of factors, including things such as the motion of its molten core, oceans and atmosphere.

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‘2021 will be the shortest year in decades’

Due to this increase in rotation speed, the average day in 2021 is expected to be 0.05 milliseconds shorter than the 86,400 seconds that normally make up the 24 hour period, according to Graham Jones, astrophysicist and science communicator, and Konstantin Bikos, editorial team lead at Time and Date.

“In fact, the year 2021 is predicted to be the shortest in decades. The last time that an average day was less than 86,000 seconds across a full year was in 1937,” Jones and Bikos explain in a post on Time and Date.

The pair go on to say that, if the Earth’s rotation gets too far out of sync with the “super steady beat of atomic clocks”, then a positive or negative “leap second” can be used to bring it back into alignment.

‘Clocks would skip a second’

Jones and Bikos explain: “Since the system of leap seconds was introduced in 1972, the Earth’s rotation has generally been a bit sluggish. So far, there have been 27 leap seconds, and they have all been positive.

“In other words, they have all added an extra second to our clocks, enabling the Earth to catch up.”

However, recently, the Earth has been getting faster, so no leap seconds have been required since 2016. If the Earth continues to speed up, then we may need to implement a “negative leap second”.

“If this happens, our clocks would skip a second, in order to keep up with the hurrying Earth,” Jones and Bikos write.

‘Possibility of a leap hour’

Physicist Peter Whibberley of the National Physics Laboratory in the UK told The Telegraph: “It’s quite possible that a negative leap second will be needed if the Earth’s rotation rate increases further, but it’s too early to say if this is likely to happen.

“There are also international discussions taking place about the future of leap seconds, and it’s also possible that the need for a negative leap second might push the decision towards ending leap seconds for good.”

Additionally, some scientists from the International Telecommunication Union have theorised that it would be better to just let the gap continue to grow, and only adding a “leap hour” where necessary.

Are leap seconds connected to leap years?

The National Institute of Standards and Technology (NIST) says that leap seconds and leap years “are both implemented to keep our time in accordance with the position of Earth”.

Leap seconds are added when needed, based on measurements, whereas leap years are regularly occurring events “based on set rules”.

NIST says: “During leap years, an extra day is added as February 29th to keep the calendar synchronised with the precession of the Earth around the Sun.

“Leap years are necessary because the actual length of the year is 365.2422 days and not 365. The extra day is added every four years to compensate for most of the partial day.

“However, this is a slight over compensation, so some century years are not leap years.”