“THE SUN”

- Presentation by Sanjok Chettri

INTRODUCTION

The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radiation, and is the most important source of energy for life on Earth.

Surface Temperature : 5,772 K

Radius: 696,340 km

Age: 4.603 billion years

Distance to Earth: 149.6 million km

Mass: 1.989 × 10^30 kg

STRUCTURE OF SUN

• Core
• Radiative Zone
• Convective zone
• Photosphere (Surface)
• Granules (Grains or Patches on Sun’s Surface)
• Chromosphere (Lower Atmosphere)
• Corona (Outermost Atmosphere)

“ STRUCTURE & FUSIONS “

TEMPERATURE AND TRANISTION

We can see the Temperature cools down as we move from Core to Surface, and it again increases as we move outwards from the Surface towards Outermost Atmosphere.

Temperature & Compositions of the Sun’s Interior (from Core to Surface)

PHOTOSPHERE

The visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Photons produced in this layer escape the Sun through the transparent solar atmosphere above it and become solar radiation, sunlight. The change in opacity is due to the decreasing amount of H⁻ ions, which absorb visible light easily. The photosphere is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as LIMB DARKENING. The photosphere has a particle density of ~10²³ m⁻³. The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form.

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SOLAR GRAULATION

THE CHROMOSPHERE

The lower region of the Sun's atmosphere is called the chromosphere. It was named after the Greek root chroma (meaning color). The chromosphere appears bright red because the hydrogen in the Sun emits a reddish-colored light at high temperatures. The chromosphere is a thin layer of plasma that lies between the Sun’s Visible surface (the photosphere) and the corona (the Sun’s upper atmosphere). It extends for at least 2,000 km above the surface

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SOLAR CORONA

• Our Sun is surrounded by a jacket of gases called an atmosphere. The corona is the outermost part of the Sun's atmosphere.
• The corona is usually hidden by the bright light of the Sun's surface. That makes it difficult to see without using special instruments. However, the corona can be seen during a total solar eclipse.
• The corona extends far out into space. From it comes the solar wind that travels through our solar system. The corona's temperature causes its particles to move at very high speeds. These speeds are so high that the particles can escape the Sun's gravity.

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PROMINENCES

• A solar prominence (also known as a filament when viewed against the solar disk) is a large, bright feature extending outward from the Sun's surface. Prominences are anchored to the Sun's surface in the photosphere, and extend outwards into the Sun's hot outer atmosphere, called the corona. A prominence forms over timescales of about a day, and stable prominences may persist in the corona for several months, looping hundreds of thousands of miles into space. Scientists are still researching how and why prominences are formed.��The red-glowing looped material is plasma, a hot gas comprised of electrically charged hydrogen and helium. The prominence plasma flows along a tangled and twisted structure of magnetic fields generated by the sun’s internal dynamo. An erupting prominence occurs when such a structure becomes unstable and bursts outward, releasing the plasma.

IMAGE OF SOLAR PROMINENCE

SUNSPOTS

Sunspots are visible as dark patches on the Sun's photosphere and correspond to concentrations of magnetic field where the convective transport of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, so they appear dark. At a typical solar minimum, few sunspots are visible, and occasionally none can be seen at all. Those that do appear are at high solar latitudes. As the solar cycle progresses towards its maximum, sunspots tend to form closer to the solar equator, a phenomenon known as Sporer’s Law. The largest sunspots can be tens of thousands of kilometers across.

FACULAE

Solar faculae are bright spots in the photosphere that form in the canyons between solar granules, short-lived convection cells several thousand kilometers across that constantly form and dissipate over timescales of several minutes. Faculae are produced by concentrations of magnetic field lines. Strong concentrations of faculae appear in solar activity, with or without sunspots.

Solar Facula (Brighter Zones)

SOLAR FLARES

A solar flare is an intense localized eruption of electromagnetic radiation in the Sun’s atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, and other solar phenomena. The occurrence of solar flares varies with the 11-year solar cycle.

Solar flares are thought to occur when stored magnetic energy in the Sun's atmosphere accelerates charged particles in the surrounding plasma. This results in the emission of electromagnetic radiation across the electromagnetic spectrum.

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SOLAR CYCLE

The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the sun's activity measured in terms of variations in the number of observed sunspots on the Sun’s surface. Over the period of a solar cycle, levels of solar radiation and ejection of solar material, the number and size of sunspots, solar flares, and coronal loops all exhibit a synchronized fluctuation from a period of minimal activity to a period of maximal activity and back to a period of minimum activity.

The magnetic field of the Sun flips during each solar cycle, with the flip occurring when the solar cycle is near its maximum. After two solar cycles, the Sun's magnetic field returns to its original state, completing what is known as a Hale cycle.

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SOLAR WIND

The corona extends far out into space. From it comes the solar wind that travels through our solar system. The corona's temperature causes its particles to move at very high speeds. These speeds are so high that the particles can escape the Sun's gravity. The Solar winds have speed about 400Km/S or (1 Million Mph)

SOLAR CYCLES OVER THE YEARS

THE SOLAR MAGNETIC FIELDS

It is widely believed that the Sun's magnetic field is generated by electrical currents acting as a magnetic dynamo inside the Sun. These electrical currents are generated by the flow of hot, ionized gases in the Sun's convection zone.

The Sun rotates differentially, that is, different parts of the surface of the Sun rotate at different rates; the rotation period ranges from 27 days near its equator to more than 30 days near its poles. This uneven spin winds up the magnetic field lines of the Sun (as shown to the left). This has the same effect as one winds up a rubber band. As the winding becomes tighter, the field (rubber band) is stressed. This stress leads to the formation of Sunspots, prominences, and an active corona. When the field snaps (locally) to release the tension, flares can result. Eventually after ~ 11 years, the stress causes a global relaxation of the field which also leads to a polarity reversal. The winding process then starts over leading to another relaxation after 11 years with another polarity reversal to return to the Sun to its original state. Sunspots vary on the relaxation time scale while the total cycle seems to be twice this relaxation time.

SUN’S MAGNETIC FIELD LINE

CONCLUSION

• The Sun is a star powered by the Nuclear fusion in its core.
• When Hydrogen fuses into Helium in the Sun’s core, the energy is released in the form of light.
• The Sun polarity changes in the period of 11 years & reverts back to it’s original position in 22 years, this cycle is called Solar Cycle or Haye’s Cycle.
• Hot Plasma moves inside the sun creating magnetic fields, which in turn creates Sunspots, Solar flares, & Coronal Mass Ejections (CMEs).
• The CMEs & Solar flare merges with Solar wind and travels outwards in the space, and it have speed well over 1 Million Km/h.
• These CMEs when interacts with Earth’s magnetosphere generating Aurora, causing power blackouts and damages satellite.
• The Study of sun is important, we depend on it for light & heat, and the very basis of life depends on it.

BIBLIOGRAPHY�

• Wikipedia.com
• Google.com
• YouTube.com/crashcourse
• An Introduction to Astro Physics by Baidynath Basu

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THANK YOU!