"He it is Who made for you the night that you might rest in it, and the day giving light; most surely there are signs in it for a people who would hear." (Quran:10/67)
A focus on the first part of the verse from Quran, Allah(God) calls the attention of mankind to the alteration of day and night and all changes it brings along as signs for a mindful soul in understanding Allah(God). The insight knowledge in the alteration of day and night might count on numerous fields of science together if taken into account. In the field of Biology and Botany for instance, this phenomenon of light and dark period is explained in terms of photoperiod or Photoperiodism and explain the biological response of organisms around the world to the level of dark and light periods for initiation of growth, egg production and flowering. Many flowering plants use a photoreceptor protein, such as phytochrome or cryptochrome, as signals for these seasonal changes in the length of day and night to initiate flowering. For example, when the days are getting longer, the tree might start to produce buds and blooms, since it would sense that spring is on the way. As days shorten, the plant would start to become dormant, producing seeds for next year and taking steps to ensure that it would be ready for winter.
Another related term explaining this phenomenon in the field of life science and biology is circadian rhythm. It is considered as an internal biological clock of 24-hour cycle in the biochemical, physiological or behavioral processes of all living entities enabling then to do perform certain actions during this time of 24 hours.
The main factor that affects the circadian rhythm is the light accepted by a region in the brain (hypothalamus). However, the light that affects the circadian rhythm is highly specific (in wave length, intensity, and other attributes), and to no surprise, the corresponding attributes are found in no other than our own sun.
Straying away from what's natural can lead to sleep disorders. In the case of disregarding the natural cycle of night and day, one can experience disorders such as the circadian sleep disorder (results in insomnia or excessive sleepiness during the day) and others.
From this point of view, night means rest and reinvigoration for plants, just as it does for human beings. In human beings the hormone melatonin , secrets at night, prepares the body for sleep by slowing down peoples' physical movements and eases their minds making them sleepy. During sleep, heartbeat respiration, and blood pressure falls down. In the morning, the production of these hormones stops and the body is again stimulated for work. At the same time, sleep allows the body's muscles and tissues to repair themselves and enable the body to replace old or dead cells. As energy expenditure is reduced during sleep, the body starts storing energy throughout the night. Several chemicals vital for the immune system and growth hormones are also secreted during sleep or rest time.
"He causes the dawn to break; and He has made the night for rest, and the sun and the moon for reckoning; this is an arrangement of the Mighty, the Knowing." (Quran: 6/96)
There are so many phenomena around us that we overlook (and consider casual) due to our ignorance. The alteration of night and day is one of them. How the earth precisely rotates, how the distance between the earth and the sun stays that way, our body's the circadian rhythm, and everything we can think of, are all signs of Allah(God) showing the perfection in creation.
"And (in) the variation of the night and the day, and (in) what Allah(God) sends down of sustenance from the cloud, then gives life thereby to the earth after its death, and (in) the changing of the winds, there are signs for a people who understand." (Quran: 45/5).
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