• How does the Quran’s concept of time relate to Einstein’s theory of relativity?
• What is the significance of the Quran’s mention of time relativity?

“Is a day shorter than a year?”

Asking this question would strangely generate different replies. A rushing answer will be “Yes”. But, a smart person must ask for a further clarification. Does the question refer to the day on Earth or on another celestial body?

Colloquially, a day is the time that elapses between sunrise today and sunrise tomorrow. In Celestial Mechanics, a ‘day’ is the span of time of the rotation of a celestial object.

Astronomy refers to the civil day as the Solar or Synodic Day. We measure it according to the position of the sun in the sky. We define it as the time interval required for the sun to go from crossing the meridian (the line dividing the sky into an eastern and western half) directly opposite an observer to returning to that meridian.

Another type of day is the Sidereal Day (from Latin word ‘sidus’ meaning star), the time elapsed between two successive meridian crossings of a fixed star, and is about four minutes shorter than a solar day.

This means that a star will return to its original place in the sky four minutes earlier everyday.

A sidereal day is the actual time it takes the earth to complete one spin around itself. The earth must then turn for four additional minutes. That’s in order to bring the sun to its original point in the sky.

We calculate a month by the movement of the moon, which orbits +the earth, which orbits the sun.

The Synodic Month that we generally know is the time between two successive full moons. It’s also the period of time it takes the sun to return to its position in the sky with respect to the moon. This process takes 29.5 days. In other words, a day on the moon lasts 29.5 Earth days.

On the other hand, a Sidereal Month is about 27.3 Earth days; the time by which the moon returns to the same position with respect to the stars. Or the time it takes the moon to move completely around the Earth. Because a full moon requires a sun-earth-moon alignment, the moon must travel over two more days to get back to its original position [1].

A year for a layman lasts 365 days. But, for an astronomer it depends on whether it’s a sidereal, Julian, tropical/solar, or any other type of a year.

A dictionary definition of a year is the 365.25 solar days by which a planet revolves around the sun. It’s also the time when the sun returns back to a specific reference position in the sky.

While a Sidereal Year is the time it takes the Earth to rotate around the sun with respect to fixed stars, and is about 20 minutes longer than the solar year [2].