Why Does Fasting Duration Vary in Different Regions? Explanation from a Theoretical Physics Professor at IPB University
Fasting is an act of worship with clear time regulations, beginning at dawn and ending at sunset. However, why does the duration of fasting vary in different regions, even within the same country?
Unlike the determination of the start and end of Ramadan, which is based on the synodic movement of the moon orbiting the Earth, the daily fasting schedule is determined by the apparent movement of the sun as observed from Earth.
Professor of Theoretical Physics at IPB University, Prof Husin Alatas, explains that the difference in fasting duration in various places is due to the sun appearing to rise and set at different times. This occurs because the Earth rotates and orbits the sun, causing variations in the length of day and night in different regions.
He elaborates that the apparent daily movement of the sun is influenced by the Earth’s rotation and its orbital motion around the sun. Due to Earth’s rotation, observers on Earth experience the alternation of day and night.
“Meanwhile, regarding Earth’s orbital motion, because Earth’s rotational axis is tilted at an angle of 23,5 degrees relative to the orbital plane, the length of the day in different months can vary significantly in regions that are not precisely on the equator,” he stated.
Furthermore, Prof Husin explains that to determine the apparent daily movement of the sun, the timing of dawn is based on the observation of the appearance of the twilight phenomenon. This phenomenon occurs when sunlight, still below the horizon, is reflected by Earth’s atmosphere.
“This light appears as a thin bluish line on the eastern horizon and gradually turns yellow as the sun rises,” he explained.
Prof Husin revealed that the blue color seen at dawn is caused by Rayleigh scattering, which reflects shorter-wavelength (blue) light more effectively and at a larger scattering angle compared to longer-wavelength light.
“Dawn ends when the solar disk begins to appear on the eastern horizon, marking the sunrise,” he said.
Prof Husin added that a light phenomenon also occurs before dawn, known as false dawn. This phenomenon results from the reflection of sunlight by interplanetary dust outside Earth’s atmosphere.
“Unlike true dawn, which has a horizontal pattern, false dawn appears as a vertical, faint glow rising upward,” he noted.
Meanwhile, the timing of Maghrib (sunset prayer) is determined by observing the disappearance of the solar disk on the western horizon, marking sunset.
When the sun sets and moves below the western horizon, its light does not immediately vanish due to Earth’s obstruction. Instead, some light is still reflected by the atmosphere.
“When the reflected light disappears, Maghrib time ends, which is marked by the disappearance of the red twilight in the sky,” he explained.
The red wavelength observed by viewers during sunset occurs because longer wavelengths scatter less in Earth’s atmosphere. “Meanwhile, shorter wavelengths are scattered first through the Rayleigh scattering mechanism, making them invisible to observers,” he concluded. (IAAS/HPH)
