Petrosains, The Discovery Centre | Discover STEM

What is Time?

Time is a progression of events from the past into the future which moves only in one direction.

Why are there 24 hours in a day?

Ancient Days

Ancient Egyptians created the 24 hours/day which they used the T-shaped bar to divide the time into 2 parts – 12 hours of darkness and 12 hours of light.

Present Days

Earth rotates once every 86,400 second which equal to 24 hours or one solar day.

How does the earth rotate and revolve?

The earth rotates around its axis as it revolves around the sun.

As the earth rotates and revolves, one part that is exposed to the sun will experience hot and bright while the other part would be frozen and dark.

It takes the earth 24 hours to make one complete rotation around its axis and 365 days to complete a revolution.

Why a day on earth now shorter than 24 hours?

Scientists have suggested that the earth is now spinning faster than it has in the last half of the century.

Average day on earth will be 0.05 milliseconds shorter than the usual 86,400 seconds that makes up the 24 hours in a day.

Factors affecting the spinning of the earth

Earthquake

Earthquake in Tohoku Japan 2011 has shortened the Earth’s day by 1.8 microseconds and shifted its figure axis by 17 centimetres.

Global Warming

As the oceans warm up, Earth will start rotating a wee bit faster, reducing the length of a day.

How do scientist find out that earth is speeding up?

1. Measure the length of day officially
Scientists measure the precise moments a fixed star passes a certain location in the sky each day.

2. Global Navigation Satellite System (GNSS) orbit computations
GNSS based systems can always access multiple satellite systems for better accuracy.

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