Have you ever wondered which day of the year has the most hours of sunshine and why? Many associate the increase in sunlight with the arrival of summer, but behind this phenomenon lies a fascinating mix of astronomy, physics, history, and even aspects of human health and psychology. Understanding how and why the number of hours of sunlight we receive varies not only satisfies our curiosity but also helps us better enjoy our surroundings and take care of our health.
In this article, you'll find an in-depth explanation of the causes of the longest day of the year, as well as scientific and cultural curiosities, the effects it has on our bodies and the environment, and useful tips for making the most of the long days of daylight. Plus, we'll debunk some myths and discover surprising facts about the Sun and its influence on Earth. Get ready for an exciting journey that goes far beyond looking at a clock or waiting for the sunset.
Why is there one day with more hours of sunshine than the rest?
The main explanation for the phenomenon of the longest day of the year is found in the tilt of the Earth's axis.The Earth revolves around the Sun, but its axis is tilted about 23,5° relative to the plane of its orbit. This means that the northern and southern hemispheres receive different amounts of sunlight throughout the year.
El Summer Solstice occurs when, in the Northern Hemisphere, the North Pole is tilted most directly toward the Sun. This usually occurs between June 20 and 21. At that time, the solar path reaches its highest point in the sky and the number of daylight hours is maximum, while the night is shorter.
Important: Although this is the day with the most light, it's not necessarily the hottest. The atmosphere and oceans slow the absorption and release of solar energy, so the peak of the heat typically shifts to July or August.
Why doesn't the day with the most light coincide with the hottest day?
There's a widespread belief that the sunniest day will also be the hottest, but the reality is more complex. The planet, like a furnace, needs time to warm up. The solar energy absorbed during the summer solstice is released gradually, which is why peak temperatures aren't reached until weeks later. The so-called "thermal lag effect" explains why July and August are typically the hottest months in the Northern Hemisphere..
This phenomenon has a lot to do with the heat capacity of the oceans and atmosphere: both accumulate part of the heat received and gradually release it, delaying the maximum temperature with respect to the maximum insolation.
Differences in day length according to latitude
The latitude of each location determines how many hours of sunshine we receive at the solstice.For example, on the Iberian Peninsula, there are areas where the difference is significant: in the north, for example in La Coruña, the longest day can last more than 17 hours. Meanwhile, in the south of Gran Canaria, it barely lasts 13 hours and 45 minutes.
In Nordic countries, the days of daylight seem endless, with the sun even not setting for days at a time in polar latitudes! The further north or south of the equator you are, the greater the difference between winter and summer in terms of the number of hours of sunlight.
The Sun and its importance for life
The Sun is much more than a source of light: it is the basis of almost all the energy that drives the climate system and life on Earth..
- It is the closest star to our planet, located about 149,6 million kilometers from us.
- It occupies 99,8% of the mass of the Solar System; the rest, mainly, is Jupiter.
- It is basically made up of hydrogen (74%) and helium (24%), with barely 2% of other elements.
Thanks to its radiation, which travels through space in about 8 minutes, the Earth receives heat and light, enables photosynthesis in plants, regulates the circadian cycles of living beings, and activates essential biological processes.
Scientific curiosities about the Sun and its effects
The Sun is not standing still: it travels around the center of the Milky Way at 220 km per second. Furthermore, its core reaches temperatures of about 15 million degrees Celsius, and the light it emits takes about eight minutes to reach Earth's surface. Curiously, from space the sun appears white, but our atmosphere makes it appear yellow at low altitudes.
Other striking facts:
- The age of the Sun is around 4.600 billion years..
- Every 10 billion years it becomes 10% brighterIn hundreds of millions of years, this will make life as we know it impossible.
- Solar influence reaches the tidesTogether with the Moon, the Sun is responsible for the movement of water in oceans and seas.
- Solar radiation can degrade materials: for example, All American flags on the Moon have turned white due to solar radiation.
The relationship between daylight, health and mood
Humans, like all other animals, We are closely linked to the rhythms set by the Sun. In fact, the so-called circadian rhythm regulates our sleep, our appetite and even our mood.
At the base of the brain there is a structure called suprachiasmatic nucleus (SCN), considered the body's "master clock." It receives information from light through cells in the retina and synchronizes basic life functions: sleep, temperature, metabolism, and even hormone production. The variation in daylight hours during each season can influence neurotransmitters such as serotonin and melatonin, altering our mood.
The longest day in Spain and regional differences
In Spain, the day with the most hours of sunshine coincides with the summer solstice., but there is considerable variability depending on the region. While in the north the day can reach more than 17 hours of daylight, in the Canary Islands it remains around 13-14 hours. The point of minimum daylight duration within the peninsula is Tarifa, in the south, with days slightly less than 15 hours.
This difference is primarily due to latitude: the greater the distance from the equator, the greater the length of the day between winter and summer. Thus, northern summers are noticeably brighter, making the evenings seem endless.
Effects and risks of prolonged sun exposure: the good and the bad
Sunbathing every day has benefits, but also risks. Sunlight is essential for synthesizing vitamin D, vital for bone health, the immune system, and the prevention of diseases such as osteoporosis. Adequate vitamin D levels have even been linked to the prevention of certain types of cancer and diabetes.
However, excessive exposure, especially during peak UV radiation hours (between 10 a.m. and 16 p.m.), can cause skin damage: sunburn, premature aging, cellular DNA damage, and, in the long term, increases the risk of melanoma and other types of skin cancer. Photoaging appears as wrinkles, spots and loss of elasticity in the skin., often accentuated by prolonged exposure to the sun.
A case cited by science, published in The New England Journal of Medicine, shows how a asymmetrical and prolonged exposure to the sun (for example, a truck driver with one half of his face more exposed) It can cause noticeable aging and cellular damage in the most exposed area. These effects can be mitigated with sunscreen, antioxidant treatments, and avoiding peak radiation hours.
Changes in behavior and mental health due to light duration
Science has proven that Daylight duration has measurable effects on health and behaviorRecent research has found that changes in the amount of light can alter the expression of neurotransmitters in the brain, influencing energy, sleep patterns, and social engagement. In places where winters are especially dark, mild depressive symptoms, lack of energy, or difficulty concentrating are common.
For this reason, artificial light therapies are used in some countries to counteract Seasonal Affective Disorder, improving mood and the ability to lead a more active daily life even when the sun is scarce.
The ultraviolet index and the importance of sun protection
The ultraviolet (UV) index measures the intensity of UV radiation reaching the Earth's surface.A value above 11 is considered extremely dangerous: just 5 minutes of exposure is enough for a person of medium skin tone to begin to suffer damage. In the north of the Iberian Peninsula, with UV values of 8-9, it takes 15-20 minutes. In the Canary Islands, UV values tend to be particularly high, necessitating extreme precautions.
A common misconception is that cloudy days protect against sunburn. In reality, clouds only slightly reduce the intensity and diffuse the radiation; sun protection is still essential even if we can't see the sun clearly.
Solar radiation and the behavior of natural elements
The influence of the Sun goes even further in nature:
- Some plants, such as bananas, grow curved because they orient themselves towards sunlight (phototropism).
- Jellyfish, which are mostly made of water, can evaporate if exposed to the sun.
- Beach sand or snow reflect sunlight (albedo effect), so we tan or burn more quickly in these environments due to the increased radiation received.
The Sun and the Earth's energy system
The amount of energy the planet receives depends on the position of the Sun and the state of its atmosphere. If we didn't have an atmosphere, Earth would receive approximately 1.367 W/m2, but in reality, this amount is reduced and varies depending on factors such as cloud cover, beam angle, and latitude.
This energy value is highest in summer, especially in places like the Canary Islands, where it can reach almost 1.200 W/m2, compared to 900 W/m2 in the north of the peninsula.
The Sun and Human Cultures: History and Celebrations
The “day with the most hours of sunshine” has been a cause for wonder and celebration since ancient times:
- The Egyptians They aligned the pyramids so that the sun would fall between them at the summer solstice.
- In the Inca CultureInti Raymi coincided with the winter solstice in the southern hemisphere, including great celebrations, offerings and rituals.
- Remains in Mayan cities indicate a concern for recording the solstices and organizing social and religious life around them.
- In Europe, Stonehenge It appears aligned to receive the first ray of the solstice sun.
Time changes and adaptation of the biological clock
In addition to the seasonal change in daylight saving time, observing daylight saving time has effects on our bodies. The "late" or "earlier" time can cause minor changes in sleep, appetite, and mood, especially in children and the elderly.
Adapting to the new schedule takes days, and regular exposure to sunlight and maintaining routines help reset the internal clock. Neurophysiology experts recommend sleeping on the new schedule and gradually adjusting your eating and activities.
A day with more daylight is not only an astronomical phenomenon, but also an event that influences traditions, health, and daily life. The effects, both positive and negative, underscore the importance of the Sun in the history and present of humanity. Knowing how to take advantage of the longer days and protect ourselves from possible excess radiation helps us enjoy sunlight wisely and with well-being.