What is Photosphere?
The Sun is considered as the centre of our solar system which also consists of planets, satellites, etc. Hydrogen and Helium are the two most elements of its composition. It has a different structure consisting of Internal and external structure. Different ranges of temperature can be observed in these layers which have their own significance. In this article, we will cover one of these layers i.e. Photosphere of the sun. We will learn what is the photosphere, its definition, its features and other related aspects as well. This topic is very much essential in the fields of Astronomy, Geography, and Earth Science.
Introduction
The atmosphere of the sun is composed of different layers and gases. It has outer and inner layers. The inner layer of the sun is the core, radiative zone and convection zone while the photosphere, the chromosphere, the transition region and the corona are the outer layers of the sun. Out of these, we talk about the main photosphere which is the outer layer of the earth. The photosphere is the external layer of the Sun which is known as the luminous envelope or the visible layer of the sun from which light as well as heat radiate. The lowest visible layer of a star is the photosphere. It is located under the chromosphere and the corona. In the universe, the stars have no gases but the gas beneath the photosphere is opaque. So, the photosphere acts as their effective visible surface.
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Photosphere of the Sun
The lowest layer of the sun is the photosphere. It is the outer layer of the sun. The term photosphere derived from the ancient Greek roots, photos means "light" and sphaira means "sphere" which refers to being a spherical surface. It is the deepest region of the luminous object. It is composed of convection cells which are called granules. Granules are cells of plasma that are 1000 km in diameter with hot rising plasma in the centre and the cooler plasma laying in the narrow spaces between them. It is flowing at a velocity of 7 km/second. The thickness of the photosphere is 500 kilometres. At this layer, the energy of the sun is released in the form of light. This is the layer of the sun from which most of the light of the sun comes out. Because of the distance between the earth and the sun, the light of the sun reaches the earth in eight minutes. It is the most visible surface of the sun. It is the part from where the sun's light reaches directly to the Earth. The sun is so distant from the earth as the edge of the photosphere appears sharp to the naked eye. But the sun has no surface because it is too hot to be a matter in it. But it is in the plasma state, that is a gas. The sun has so many gases composed of ionized atoms.
The temperature in the photosphere ranges from 4,100 °C or 7,400 °F at the top to 9,700 °C or 17,500 °F. In this layer, photons that are generated are deeper. This cannot get out without any absorption and remission. The density of the ionized gas is the same as air at the earth's surface. The density of ionized gas is 1/1,000. But it is more opaque. It is because of the absorption of the strong light by the hydrogen ions.
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Definitions of Photosphere of the Sun
Some of the standard definitions are given below:
"Photosphere is a sphere of light or radiance or the luminous surface layer of the sun or a star." - Merriam-Webster
"Photosphere is the visible surface of the sun, several hundred kilometres thick or a sphere of light or radiance or the luminous visible surface of the sun, being a shallow layer of strongly ionized gases." - Collins Dictionary
Features of the Photosphere
The features of the photosphere are mentioned below:-
The presence of dark sunspots.
Bright faculae
Granules
By the Doppler effect, we can measure the material of the flow in the photosphere.
It consists of super-granules and large scale flows as well as patterns of waves and oscillations.
It is the most visible surface of the sun.
The temperature of the photosphere is 5,780 degrees as compared to the temperature of the inside of the sun.
It is measured in millions of degrees.
The edge of the atmosphere is also measured in degrees.
If we talk about the location of the photosphere, it is located above the solar convection zone where heat from the core radiates outward.
The gases which are made in the photosphere are totally opaque means that we cannot see through them.
The photosphere is constructed from the convection of the cells which are called granules.
It produces a boiling effect and lives from 8-9 minutes.
Sunspots are the cooler region of the photosphere. It is dark in colour because of its lower temperatures.
Sunspots
The areas which appear dark on the surface of the sun are called sunspots. It is a temporary phenomenon in the sun's photosphere. It is darker than the other surrounding areas. It is the place where the magnetic field is about 2,500 times stronger than the earth's. The most higher magnetic field is there than anywhere else in the sun. The temperature increases because of the strong magnetic field and the surrounding atmospheric temperature decreases. That is why the temperature in the sunspots turns lower than in the surroundings.
The magnetic fields pointing in opposite directions, here sunspots occur in pairs. The region which appears as dark is called "umbra" and the region which is surrounded by light is called "penumbra." The sunspots look dark because the surrounding surface of the photosphere is about 10,000 degrees Fahrenheit while the surface which is dark is about 6,300 degrees Fahrenheit. The disturbances in the sun's magnetic field running over the photosphere which is the visible surface of the sun. The size of the sunspots is as an average or the same size as earth.
Why is the Photosphere Cooler than Corona?
As we all know, the photosphere is the visible surface of the sun. It is the first layer of the sun. It is the outer layer of the sun that is present outside of the core. Because of this, it is the coldest layer of the sun. The corona is the outermost layer of the sun and it is hotter than the photosphere. The chromosphere is the layer between the corona and photosphere. This layer of the Sun is considered the visible surface of the sun. The dark areas are present on it that are cooler than the surroundings. That is why the photosphere is cooler than the corona.
Conclusion
To conclude, we said that the photosphere is the outermost layer of the sun. It is the lowest visible surface of the sun. It is a yellow coloured layer that is thick. The thickness of the layer is about 300 miles(500 kilometres). There are hot gases present in the layer which is known as sunspots. It is composed of convection cells i.e. granules. It is present in 1000 kilometres in the centre and it is flowing at the velocity of 7 kilometres per second. The temperature of the layer is 5,780 degrees as compared to the temperature in the sun. The gases which are present in the layer made it opaque. This article will help whenever you are studying the Sun and its various layers in Science or Astronomy.
FAQs on Photosphere
1. What is the photosphere of the Sun?
The photosphere is the lowest layer of the Sun's atmosphere and is the visible surface we see from Earth. The name originates from the Greek words 'photos' (light) and 'sphaira' (sphere), literally meaning a "sphere of light." It is the specific region from which most of the Sun's light and heat are radiated directly into space.
2. What are the main features observed on the Sun's photosphere?
The photosphere has a distinct, mottled appearance due to several key features, which include:
- Granules: These are bubbling patterns of hot, rising plasma (convection cells) that cover the entire surface, each lasting for about 10-20 minutes.
- Sunspots: These are cooler, darker areas that appear where the Sun's powerful magnetic field breaks through the surface, inhibiting heat flow.
- Faculae: These are bright, hot spots that are often found near sunspots and contribute to the Sun's overall luminosity.
3. What is the average temperature and thickness of the photosphere?
The photosphere has an average temperature of about 5,500 degrees Celsius (or around 6,000 Kelvin). Despite the Sun's immense size, the photosphere is a relatively thin layer, with an estimated thickness of only about 400 to 500 kilometres.
4. What is the composition of the Sun's photosphere?
The photosphere is primarily composed of extremely hot gases in a plasma state. The main elements are hydrogen (making up about 90% of the atoms) and helium (about 10%). It also contains trace amounts of other heavier elements like oxygen, carbon, neon, and iron.
5. Why is the photosphere considered the Sun's "surface" if the Sun is a ball of gas?
This is an excellent question that addresses a common misconception. The Sun does not have a solid surface like Earth. The photosphere is defined as the "surface" because it represents the layer where the Sun's gas becomes opaque to light. Below this layer, the gas is too dense for light to escape directly. Above it, the gas is thin enough for light photons to travel freely into space. Therefore, it marks the visible boundary of the Sun that we can observe.
6. How is the photosphere different from the chromosphere?
The photosphere and the chromosphere are two adjacent layers of the Sun's atmosphere with key differences:
- Position: The photosphere is the lowest, visible layer, while the chromosphere sits directly above it.
- Temperature: The photosphere is cooler, at around 5,500°C. Paradoxically, the chromosphere above it is hotter, with temperatures rising from 6,000°C to about 20,000°C.
- Visibility: We see the photosphere as the Sun's bright disc. The much fainter chromosphere is only visible during a total solar eclipse, where it appears as a distinct reddish ring.
7. How do phenomena like sunspots and granules form on the photosphere?
These features are direct results of the dynamic processes of energy transfer and magnetic activity within the Sun. Granules are the tops of convection currents, where hot gas from the Sun's interior rises, cools at the surface, and sinks back down. Sunspots are formed by intense, localised magnetic fields that disrupt this convection, blocking the flow of heat from below and making the area cooler and darker than its surroundings.
8. What is the importance of studying the photosphere for us on Earth?
Studying the photosphere is crucial because it is the source of almost all the solar energy that makes life on Earth possible. Furthermore, observing its features, like the development of sunspots and the occurrence of solar flares that are rooted in it, helps scientists understand and predict space weather. This is vital for protecting our satellites, communication networks, and power grids from solar storms.
9. Why does the edge of the Sun's disc appear darker than its centre in photographs?
This visual effect is known as limb darkening. When we look at the centre of the Sun, our line of sight penetrates deeper into the hotter, brighter layers of the photosphere. In contrast, when we look towards the Sun's edge (its limb), our view passes through the upper, cooler, and less dense layers of the photosphere. Since these upper layers are cooler, they emit less light, causing the edge to appear dimmer than the centre.
10. How does the energy created in the Sun's core reach us as light from the photosphere?
Energy produced by nuclear fusion in the Sun's core travels outwards for thousands of years through the radiative and convective zones. When this energy reaches the top of the convective zone, it heats the plasma that constitutes the photosphere. It is in this layer that the density of the gas drops enough for photons (particles of light) to finally escape and travel unimpeded through space. The photosphere, therefore, functions as the final release surface for the Sun's visible energy.
