Internal Structure

Very few questions are asked in prelims [time to benefit ratio is too low] from this section. You can ignore these concepts if you found them too scientific.

Sun

· Age => 4.6 billion years

· Diameter => 13,91,785 km (~1.3 million km)

· Temperature => 6000 C on surface and 16 million C in core

· Density => 1.41 times that of water

· Period of rotation => 25 days 9 hrs

· Speed of rotation => 7179.73 km/hr (Earth’s rotational velocity => 1675Km/hr)

· Equivalent to 3,32,900 Earth masses.

· Compared to the majority of stars in the Milky Way, the Sun is rather large and bright.

· Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, are common, making up 85% of the stars in the galaxy.

· Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum due to the differential rotation within the gaseous Sun.

· The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium. Jupiter and Saturn, which comprise nearly all the remaining matter, possess atmospheres composed of roughly 99% of these elements.

Sun – Internal Structure – Atmosphere

· 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, and the corona.

· Beyond that is the solar wind, an outflow of gas from the corona.

Photosphere

· The photosphere is the bright outer layer of the Sun that emits most of the radiation.

· The photosphere is an extremely uneven surface.

· The effective temperature on the outer side of the photosphere is 6000°K (11,000°F).

Chromosphere

· Just above the photosphere is the chromosphere.

· It is relatively a thin layer of burning gases.

Sunspot

· A dark patch on the surface of the Sun is known as sunspot.

· Sunspots appear as dark areas because they are about 1500° cooler than the surrounding chromospheres.

· The individual sunspot has a lifetime ranging from a few days to a few months.

· Each spot has a black center or umbra, and a lighter region or penumbra, surrounding it.

· It has been suggested that the Sun is 1% cooler when it has no spot, and that this variation in solar radiation might affect the climates of the Earth.

Solar Wind

· Stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun at speeds as high as 900 km/s and at a temperature of 1 million degrees (Celsius).

· It is made of plasma.

Effects

· As the solar wind approaches a planet that has a well-developed magnetic field (such as Earth, Jupiter and Saturn), the particles are deflected.

· This region, known as the magnetosphere, causes the particles to travel around the planet rather than bombarding the atmosphere or surface.

· The magnetosphere is roughly shaped like a hemisphere on the side facing the Sun, then is drawn out in a long trail on the opposite side.

· The boundary of this region is called the magnetopause, and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines.

· The solar wind is responsible for the overall shape of Earth’s magnetosphere.

· Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind.

· Venus, the nearest and most similar planet to Earth in the Solar System, has an atmosphere 100 times denser than our own, with little or no geo-magnetic field. This is an exception.

Solar flares

· Produced due to magnetic anomalies.

· A magnetic storm on the Sun which appears to be a very bright spot and a gaseous surface eruption.

· The high magnetic fields in the sunspot-producing active regions give rise to explosions known as solar flares.

· As solar flares push through the corona, they heat its gas to anywhere from 10 to 20 million K.

Solar prominence

· An arc of gas that erupts from the surface of the Sun.

· Prominences can loop hundreds of thousands of miles into space.

· Prominences are held above the Sun’s surface by strong magnetic fields and can last for many months.

· At some time in their existence, most prominences will erupt, spewing enormous amounts of solar material into space.

Corona

· A corona is a distinctive atmosphere of plasma that surrounds the Sun and other celestial bodies.

· The Sun’s corona extends millions of kilometres into space and is most easily seen during a total solar eclipse

Plasma

· One of the four fundamental states of matter, the others being solid, liquid, and gas.

· Plasma is simply ionized gas [convert (an atom, molecule, or substance) into an ion or ions, typically by removing one or more electrons]

· Lightning and electric sparks are everyday examples of phenomena made from plasma.

· Neon lights could more accurately be called “plasma lights”, because the light comes from the plasma inside of them.

Aurora

· An aurora is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions. [This is due to magnetic field lines of earth]

· Auroras are caused by charged particles, mainly electrons and protons, entering the atmosphere from above causing ionization and excitation of atmospheric constituents, and consequent optical emissions.