It hits your face on a Tuesday morning and suddenly the world feels slightly less heavy. We call it "good weather," but scientifically, it's a massive nuclear explosion 93 million miles away sending packets of energy—photons—hurtling through the vacuum of space to smack into your retinas. When people ask what is the sunshine, they usually aren't looking for a physics lecture on solar fusion. They’re asking about that feeling. That biological "click" that happens when light touches skin.
Sunshine is more than just light. It is a spectrum of electromagnetic radiation, a mix of infrared, visible light, and ultraviolet (UV) rays that dictates almost every biological rhythm we have. Without it, we're basically indoor plants with anxiety.
The Massive Nuclear Reactor in the Sky
To understand what is the sunshine, you have to look at the Sun's core. It’s hot. About 15 million degrees Celsius hot. Through a process called nuclear fusion, hydrogen atoms smash together to form helium, releasing an unfathomable amount of energy. This energy travels from the core to the surface, and then it takes about eight minutes and twenty seconds to reach Earth.
Think about that. The light hitting your toast this morning started its journey through the solar system before you even finished brewing your coffee.
Sunshine is composed of three main parts that matter to us on the ground. First, there's visible light. That’s what lets you see the color of your car or the person sitting across from you. Then there's infrared radiation. You can't see it, but you feel it as heat. Finally, there's ultraviolet radiation. This is the tricky stuff. UV radiation is split into UVA, UVB, and UVC. Most UVC is blocked by the ozone layer (thankfully), but UVA and UVB get through, and they are responsible for everything from your summer tan to the structural damage in your DNA that causes skin cancer.
Why Your Brain Breaks Without It
Most people think of Vitamin D when they think of the sun. But the psychological impact of what is the sunshine is arguably just as important. Your eyes have specific cells called photosensitive retinal ganglion cells. They don't help you "see" images; instead, they track the intensity of blue light in the environment to tell your brain what time it is.
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When sunshine hits these cells, it triggers the suprachiasmatic nucleus (SCN) in your hypothalamus. This is your body's master clock. It tells your brain to stop producing melatonin (the sleep hormone) and start pumping out serotonin.
Have you ever felt that "Seasonal Affective Disorder" (SAD) kick in during a particularly grey February? That isn't just "the blues." It’s a literal chemical shift. Dr. Norman Rosenthal, the psychiatrist who first described SAD in the 1980s, noted that for many people, the lack of full-spectrum light leads to a drop in serotonin that mimics clinical depression. Sunshine is, quite literally, a mood-regulating drug delivered via the sky.
The Vitamin D Factory on Your Skin
Here is the wild part about what is the sunshine: it’s a catalyst for manufacturing. Your body doesn't just "absorb" Vitamin D from the sun. It makes it. When UVB rays hit your skin, they interact with a protein called 7-dehydrocholesterol. This interaction converts the protein into vitamin D3.
Vitamin D isn't even really a vitamin; it’s a pro-hormone. It’s essential for calcium absorption, which keeps your bones from turning into chalk. But more recent research, including studies from Harvard Medical School, suggests that Vitamin D receptors are found in almost every cell in the human body. It plays a role in immune function, muscle strength, and even how your heart beats.
But there’s a catch.
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If you live north of a certain latitude—think Seattle, London, or Berlin—the sun’s angle in the winter is too low for UVB rays to penetrate the atmosphere effectively. You could stand outside naked in Anchorage in January and you still wouldn't produce Vitamin D. This "Vitamin D winter" is why many people in northern climates feel physically exhausted by March.
The Dark Side: When Light Attacks
It isn't all golden hours and picnics. Sunshine is also a carcinogen. It sounds harsh, but it’s true. UVA rays penetrate deep into the dermis, the skin’s thickest layer. This leads to premature aging and wrinkling—what dermatologists call photoaging. UVB rays are shorter and primarily responsible for sunburns.
Both types damage the DNA in skin cells. If the body can't repair that damage, cells can begin to grow uncontrollably, leading to melanoma or basal cell carcinoma. This is the paradox of what is the sunshine. It is the source of all life on this planet, yet it is also capable of destroying the very biological blueprints that keep us alive.
The trick is the dose. A "healthy tan" is actually a sign of DNA damage; the skin produces melanin as a shield to prevent further injury. It's your body's way of saying, "Please, stop."
Sunshine as an Economic Engine
If you look at history, sunshine has dictated where we live and how we work. Before the lightbulb, human productivity was chained to the sun. We woke with it; we slept with it. Today, we try to ignore it with LED screens and 24-hour shifts, but our biology is still stuck in the Pleistocene.
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Real estate prices are higher for "sun-drenched" apartments. Tourism economies in the Caribbean or the Mediterranean are built entirely on the commodification of the sun. We travel thousands of miles just to sit in a specific intensity of light. Honestly, we’re just big, complicated lizards looking for a warm rock.
Circadian Rhythms and the Blue Light Myth
You've probably heard that you should avoid blue light from your phone before bed. That's because your phone is trying to mimic what is the sunshine at high noon.
The sun emits a lot of blue light in the morning and midday. This signals alertness. As the sun sets, the light shifts toward the red end of the spectrum. This shift allows the brain to begin the "wind-down" process. When you stare at a screen at 11:00 PM, you’re telling your brain that it’s actually 12:00 PM on a bright July day. Your SCN gets confused, melatonin stays suppressed, and you wake up feeling like a zombie.
How to Actually Use the Sun
Knowing what is the sunshine doesn't do much good if you're stuck in a cubicle all day. To get the benefits without the rot, you have to be intentional.
- Get outside within 30 minutes of waking up. Even if it's cloudy. Cloud cover still allows significantly more photons to hit your eyes than indoor lighting. This sets your circadian clock for the entire day.
- Understand the "Shadow Rule." If your shadow is shorter than you are, the sun’s rays are at their most intense. This is when you make the most Vitamin D, but it’s also when you’re most likely to burn. 10 to 15 minutes is usually enough for most light-skinned people; those with darker skin may need longer.
- Don't forget the eyes. While you need light in your eyes to set your clock, direct UV exposure can cause cataracts and macular degeneration. Wear polarized sunglasses once you've had your morning "dose" of light.
- Check the UV Index. Most weather apps now have a UV Index rating. If it's above 6, you need protection. If it's 1 or 2, you're probably safe to linger a bit longer.
Sunshine is the most fundamental part of our environment, yet we've largely moved away from it. We live in boxes, work in boxes, and drive in boxes. Reconnecting with the light isn't just about a tan; it's about syncing your internal chemistry with the rhythm of the planet.
Start by taking your morning coffee on the porch or walking around the block during your lunch break. The photons are there, waiting to hit your skin and flip the switches that make you feel human. Just don't overdo it. The sun is a magnificent, life-giving furnace, but it doesn't care about your skin's integrity. Respect the power of the star you're orbiting.