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The bright, visible surface of the Sun, from which most of its light is given out, is called the:
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Answer: Option A ā Photosphere
Detailed Solution
The photosphere is the visible surface of the Sun, the layer from which most of the sunlight we see is emitted. The word comes from the Greek "photos" (light) and "sphaira" (sphere).
Features of the photosphere:
- It is a layer about 400 to 500 km thick.
- Its temperature is about 5,500 degrees Celsius (about 5,800 Kelvin).
- It has a grainy appearance, called granulation, caused by rising and sinking currents of hot gas.
Sunspots appear on the photosphere. They are cooler, darker regions (about 3,500 to 4,500 degrees Celsius) caused by strong magnetic activity.
The number of sunspots rises and falls in a cycle of about 11 years.
Layers of the Sun from inside to outside:
Core: the central region where nuclear fusion converts hydrogen into helium, releasing enormous energy. Its temperature is about 15 million degrees Celsius.
Radiative zone: energy moves outward slowly as radiation.
Convective zone: hot gas rises and cooler gas sinks, carrying energy to the surface.
Photosphere: the visible surface.
Chromosphere: a thin, reddish layer above the photosphere, seen briefly during certain eclipses.
Corona: the outermost layer, a faint halo of extremely hot gas that extends millions of kilometres into space.
The corona puzzle:
The corona is much hotter (1 to 3 million degrees Celsius) than the photosphere, even though it is farther from the core. Why this happens is still being studied.
Composition of the Sun:
About 73 percent hydrogen and 25 percent helium by mass, with small amounts of other elements.
Studying the Sun:
India's Aditya-L1, launched on 2 September 2023, is the country's first space-based solar observatory. It orbits the Sun-Earth Lagrange point L1, about 1.5 million km from the Earth.
NASA's Parker Solar Probe has flown closer to the Sun than any other spacecraft, passing through the corona.
Why not the other options?
- āThe chromosphere and corona are layers above the photosphere.
- āThe core is the innermost region, where energy is produced.
Quick tip
Remember: Sun's layers (inside to outside) = core, radiative zone, convective zone, photosphere (visible surface), chromosphere, corona.
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This question tests your understanding of Universe & Solar System, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the universe, galaxies and stars, the solar system and its planets, dwarf planets, moons, asteroids, comets and meteors, and the Earth's motions, including rotation, revolution, seasons, latitudes, longitudes and time zones. Common questions ask about the largest and smallest planets (Jupiter and Mercury), the hottest planet (Venus), the 'Red Planet' (Mars), and planets with the most moons. Other frequent questions cover solstices and equinoxes, the International Date Line, and Indian Standard Time, which is based on the 82.5 degree E meridian. Practise the universe and solar system questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.