The Sun

Introduction :

The Sun is the star at the centre of the Solar System. It is a nearly perfect sphere of hot plasma, with an internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometres (864,000 miles), or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Roughly three-quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the centre, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.

Size and Distance :

With a radius of 432,168.6 miles (695,508 kilometers), our Sun is not an especially large star—many are several times bigger—but it is still far more massive than our home planet: 332,946 Earths match the mass of the Sun. The Sun’s volume would need 1.3 million Earths to fill it.

The Sun is 93 million miles (150 million kilometers) from Earth. Its nearest stellar neighbor is the Alpha Centauri triple star system: Proxima Centauri is 4.24 light years away, and Alpha Centauri A and B—two stars orbiting each other—are 4.37 light years away. A light year is the distance light travels in one year, which is equal to 5,878,499,810,000 miles or 9,460,528,400,000 kilometers.


Orbit and Rotation :

The Sun, and everything that orbits it, is located in the Milky Way galaxy. More specifically, our Sun is in a spiral arm called the Orion Spur that extends outward from the Sagittarius arm. From there, the Sun orbits the center of the Milky Way Galaxy, bringing the planets, asteroids, comets and other objects along with it. Our solar system is moving with an average velocity of 450,000 miles per hour (720,000 kilometers per hour). But even at this speed, it takes us about 230 million years to make one complete orbit around the Milky Way.

The Sun rotates as it orbits the center of the Milky Way. Its spin has an axial tilt of 7.25 degrees with respect to the plane of the planets’ orbits. Since the Sun is not a solid body, different parts of the Sun rotate at different rates. At the equator, the Sun spins around once about every 25 days, but at its poles the Sun rotates once on its axis every 36 Earth days.

Formation :

The Sun and the rest of the solar system formed from a giant, rotating cloud of gas and dust called a solar nebula about 4.5 billion years ago. As the nebula collapsed because of its overwhelming gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form our Sun, which accounts for 99.8% of the mass of the entire solar system.

Like all stars, the Sun will someday run out of energy. When the Sun starts to die, it will swell so big that it will engulf Mercury and Venus and maybe even Earth. Scientists predict the Sun is a little less than halfway through its lifetime and will last another 6.5 billion years before it shrinks down to be a white dwarf.


Compositions :

The Sun is composed primarily of chemical elements such as hydrogen and helium. At this time in the Sun's life, they account for 74.9% and 23.8% of the mass of the Sun in the photosphere, respectively. All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.

Internal structure and atmosphere :

The sun and its atmosphere are divided into several zones and layers. The solar interior, from the inside out, is made up of the core, radiative zone and the convective zone. The solar atmosphere above that consists of the photosphere, chromosphere, a transition region and the corona. Beyond that is the solar wind, an outflow of gas from the corona.

The core extends from the sun's center to about a quarter of the way to its surface. Although it only makes up roughly 2 percent of the sun's volume, it is almost 15 times the density of lead and holds nearly half of the sun's mass. Next is the radiative zone, which extends from the core to 70 percent of the way to the sun's surface, making up 32 percent of the sun's volume and 48 percent of its mass. Light from the core gets scattered in this zone, so that a single photon often may take a million years to pass through. The convection zone reaches up to the sun's surface, and makes up 66 percent of the sun's volume but only a little more than 2 percent of its mass. Roiling "convection cells" of gas dominate this zone. Two main kinds of solar convection cells exist — granulation cells about 600 miles (1,000 kilometers) wide and supergranulation cells about 20,000 miles (30,000 km) in diameter.

The photosphere is the lowest layer of the sun's atmosphere, and emits the light we see. It is about 300 miles (500 km) thick, although most of the light comes from its lowest third. Temperatures in the photosphere range from 11,000 F (6,125 C) at bottom to 7,460 F (4,125 C) at top. Next up is the chromosphere, which is hotter, up to 35,500 F (19,725 C), and is apparently made up entirely of spiky structures known as spicules typically some 600 miles (1,000 km) across and up to 6,000 miles (10,000 km) high. After that is the transition region a few hundred to a few thousand miles thick, which is heated by the corona above it and sheds most of its light as ultraviolet rays. At the top is the super-hot corona, which is made of structures such as loops and streams of ionized gas. The corona generally ranges from 900,000 F (500,000 C) to 10.8 million F (6 million C) and can even reach tens of millions of degrees when a solar flare occurs. Matter from the corona is blown off as the solar wind.

Planetary System :

The Sun has eight known planets. This includes four terrestrial planets (Mercury, Venus, Earth, and Mars), two gas giants (Jupiter and Saturn), and two ice giants (Uranus and Neptune). The Solar System also has at least five dwarf planets, an asteroid belt, numerous comets, and a large number of icy bodies which lie beyond the orbit of Neptune.

Sun Facts :

  • The light from the Sun takes 8min 19sec to reach earth.

  • The energy produced on the sun is due to the thermonuclear fusion process.

  • The Sun has all the colours mixed together, this appears white to our eyes.

  • The Sun is composed of hydrogen (70%) and Helium (28%).

  • The Sun is a main-sequence G2V star (or Yellow Dwarf).

  • The Sun is 109 times wider than the Earth and 330,000 times as massive.

  • The Sun’s surface area is 11,990 times that of the Earth’s.

  • The distance between the Earth and the Sun is an Astronomical Unit (AU).

  • The Sun revolves around the centre of the Milky Way galaxy in 230 million years.

  • The Sun is an almost perfect sphere.


Core Layers of The Sun


Sun Spots


Solar Flare

Some other facts :

  1. One million Earths could fit inside the Sun. A hollow Sun would fit around 960,000 spherical Earths. If squished inside with no wasted space, then around 1,300,000 would fit inside. The Sun’s surface area is 11,990 times that of the Earth’s.

  2. The Sun contains 99.86% of the mass in the Solar System. The mass of the Sun is approximately 330,000 times greater than that of Earth. It is almost three-quarters Hydrogen, whilst most of the remaining mass is Helium.

  3. The Sun is an almost perfect sphere. There is a 10-kilometre difference between the Sun’s polar and equatorial diameter. This means it is the closest thing to a perfect sphere that has been observed in nature.

  4. The Sun will consume the Earth. When the Sun has burned all its Hydrogen, it will continue to burn helium for 130 million more years. During this time, it will expand to the point that it will engulf Mercury, Venus, and the Earth. At this stage, it will have become a red giant

  5. The Sun will one day be about the size of Earth. After its red giant phase, the Sun will collapse. It will keep its enormous mass with the approximate volume of our planet. When this happens, it will have become a white dwarf.

  6. The temperature inside the Sun can reach 15 million degrees Celsius. Energy is generated at the Sun’s core, by nuclear fusion, as Hydrogen converts to Helium. Hot objects expand, the Sun would explode if it were not for its enormous gravitational force. The temperature on the surface of the Sun is closer to 5,600 degrees Celsius.

  7. Light from the Sun takes eight minutes to reach Earth. The Sun is an average distance of 150 million kilometres from the Earth. Light travels at 300,000 kilometres per second. Dividing one by the other gives us an approximate time of 500 seconds (or eight minutes and 20 seconds). Although this energy reaches Earth in a few minutes, it will already have taken millions of years to travel from the Sun’s core to its surface.

  8. The Sun travels at 220 kilometres per second. The Sun is 24,000-26,000 light-years from the galactic centre. It takes the Sun 225-250 million years to complete an orbit of the centre of the Milky Way.

  9. The distance from the Sun to Earth changes throughout the year. This is because the Earth travels on an elliptical orbit around the Sun. The distance between the two bodies varies from 147 to 152 million kilometres.

  10. The Sun is middle-aged. At around 4.6 billion years old, the Sun has already burned off about half of its store of Hydrogen. It has enough left to continue to burn Hydrogen for approximately 5 billion years. The Sun is currently a type of star known as a Yellow Dwarf.

  11. The Sun has a very strong magnetic field. Magnetic energy released by the Sun during magnetic storms causes solar flares. We see these as sunspots. In sunspots, the magnetic lines twist and they spin, much like a tornado would on Earth.

  12. The Sun generates solar wind. The wind is a stream of charged particles. This travels at approximately 450 kilometres per second through the solar system. Solar wind occurs when the magnetic field of the Sun extends into space.

  13. Sol is the Latin for Sun. This is where the word “solar” comes from, which is used to describe things that are derived from, related to, or caused by the Sun


False-colour wiggle animation of the Sun

Feature off Sun :

Sunspots :

Sunspots are areas of the Sun’s surface that appear darker than the surrounding areas, this is because they are cooler. They form in areas of strong magnetic activity that inhibit heat transfer.

Solar Flares :

When the magnetic fields near sunspots cross, tangle or are reorganized, an explosion of energy can be released. Intense solar flares can interfere with radio communications on Earth.

3 D Model of Sun

Source: NASA Visualization Technology Applications and Development (VTAD)

Source Credits : NASA, Wikipedia and Space Facts.