When's the last time you gazed upward and marveled at the mysterious, life-giving force that is the sun? Contact online >>
When''s the last time you gazed upward and marveled at the mysterious, life-giving force that is the sun?
If you believe the whole staring-at-the-sun-makes-you-go-blind thing (which is actually true), you''re probably not doing a whole lot of sun-gazing. But it''s a real marvel: The sun warms our planet every day, provides the light by which we see and is necessary for life on Earth. It can also cause cell death and make us blind. It could fit 1.3 million Earths inside its sphere [source: SpaceDaily]. It produces poem-worthy sunsets and as much energy as 1 trillion megaton bombs every second [source: Boston Globe].
Despite its magnificence and power, our sun is just a plain old average star by universal standards. It''s really proximity that makes the sun so special to Earth (along with the fact that we wouldn''t be here if it weren''t so close).
Let''s look at the parts of our nearest star, find out how it makes light and heat and explore its major features.
A 2023 study published in the journal Life suggests that life''s building blocks might have originated from interactions between the sun''s energetic particles and Earth''s early atmosphere [Phys ]. Through a series of experiments, researchers were able to demonstrate how solar particles colliding with gases like carbon dioxide, molecular nitrogen and methane could produce amino acids and carboxylic acids — fundamental components of proteins and organic life.
To better understand how life began, scientists often focus on how the pieces needed for life — amino acids — first formed. One idea, thought up in the 1800s by Charles Darwin, suggests that life might have started in a "warm little pond" of chemicals that received energy from lightning.
In 1953, Stanley Miller recreated this idea in a lab, generating amino acids from a mixture of methane, ammonia, water and molecular hydrogen exposed to simulated lightning. Subsequent research challenged Miller''s approach, revealing differences in Earth''s early atmospheric composition.
For the 2023 study, lead author Vladimir Airapetian used data from NASA''s Kepler mission to suggest that powerful solar eruptions called superflares from the young sun could have triggered chemical reactions when colliding with Earth''s atmosphere.
According to the solar nebula theory, the sun formed around 4.5 billion years ago from a massive cloud of gas and dust in space [source: NASA]. Imagine a huge cloud in space that shrinks and spins because of outside forces. This cloud becomes a flat, spinning disk, called a solar nebula. In the middle of this disk, a baby star forms and gathers material around it.
As time goes on, the planets get heated up and change inside. The sun''s energy makes a breeze that blows away leftover gas, showing us the planets, moons, asteroids and comets.
The sun is a star, just like the other stars we see in the evening sky. The difference is distance: The other stars we see are light-years away, while our sun lies only about eight light minutes away — many thousands of times closer.
Officially, the sun is classified as a G2 type star, based on its temperature and the wavelengths or spectrum of light that it emits. There are lots of G2s out there, and Earth''s sun is merely one of billions of stars that orbit the center of our galaxy, made up of the same substance and components.
The sun is composed of gas. It has no solid surface. However, it still has a defined structure. The three major structural areas of the sun are shown in the upper half of Figure 1. They include:
Above the surface of the sun is its atmosphere, which consists of three parts, shown in the lower half of Figure 1:
All of the major features of the sun can be explained by the nuclear reactions that produce its energy, by the sun''s magnetic fields resulting from the movements of the gas and by its immense gravity. (Because of its size, the sun has enough gravitational force to hold all of the planets in their orbits around the sun.)
The sun''s core starts from the center and extends outward to encompass 25 percent of the star''s radius. Its temperature is greater than 15 million degrees Kelvin [source: Montana]. At the core, gravity pulls all of the mass inward and creates an intense pressure.
These reactions account for 85 percent of the sun''s energy. The remaining 15 percent comes from the following reactions:
The helium-4 atoms are less massive than the two hydrogen atoms that started the process, so the difference in mass is converted to energy, as described by Einstein''s theory of relativity (E = mc²). The energy is emitted in various forms of light: ultraviolet light, X-rays, visible light, infrared, microwaves and radio waves.
The sun also emits energized particles (neutrinos, protons) that make up the solar wind. This energy strikes Earth, where it warms the planet, drives our weather and provides energy for life. We aren''t harmed by most of the UV radiation or solar wind because the Earth''s atmosphere protects us.
The radiative zone extends outward from the core, accounting for 45 percent of the sun''s radius. In this zone, the energy from the core is carried outward by photons, or light units. As one photon is made, it travels about 1 micron (1 millionth of a meter) before being absorbed by a gas molecule.
Upon absorption, the gas molecule is heated and re-emits another photon of the same wavelength. The re-emitted photon travels another micron before being absorbed by another gas molecule and the cycle repeats itself; each interaction between photon and gas molecule takes time.
Approximately 1,025 absorptions and re-emissions take place in this zone before a photon reaches the surface, so there is a significant time delay between a photon being made in the core and one reaching the surface.
The convection currents carry photons outward to the surface faster than the radiative transfer that occurs in the core and radiative zone. With so many interactions occurring between photons and gas molecules in the radiative and convection zones, it takes a photon approximately 100,000 to 200,000 years to reach the surface.
Just like Earth, the sun boasts it own atmosphere, which is composed of the photosphere, the chromosphere and the corona.
This is the lowest region of the sun''s atmosphere and the area that we can see. The surface of the sun typically refers to the photosphere, at least in lay terms. It is 180 to 240 miles (around 290 to 390 km wide) and between 4,000 and 6,000 degrees Kelvin (from the top to the bottom).
It appears granulated or bubbly, much like the surface of a simmering pot of water. The bumps are the upper surfaces of the convection current cells beneath; each granulation can be 600 miles (1,000 km) wide.
As we pass up through the photosphere, the temperature drops and the gases, because they are cooler, do not emit as much light energy. This makes them less opaque to the human eye. Therefore, the outer edge of the photosphere looks dark due to an effect called limb darkening that accounts for the clear crisp edge of the sun''s surface.
The area extends above the photosphere to about 1,200 miles (2,000 kilometers). The temperature rises across the chromosphere from 4,500 degrees Kelvin to about 10,000 degrees Kelvin. The chromosphere is thought to be heated by convection within the underlying photosphere.
As gases churn in the photosphere, they produce shock waves that heat the surrounding gas and send it piercing through the chromosphere in millions of tiny spikes of hot gas called spicules.
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