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Astrophysics

AN INTRODUCTION TO SOLAR PHYSICS

AN INCREDIBLE LIGHT SHOW - spaceonova

If you want to shine like a sun, first burn like a sun.

– APJ Abdul Kalam

This quote by our beloved APJ Abdul Kalam reflects the significance of the sun and how we should learn to work hard in our lives. The sun works tirelessly and gives the best to us every day. Similarly, when we strive to fulfill our dreams and persevere in our efforts, we shine. There is a huge amount of energy created in the sun and hence it is so hot and bright. Have you ever wondered what drives the sun and how it creates an almost infinite amount of energy? We feel the heat and light of the sun in the morning hours on earth. But we are almost 150 million kilometers away. That seems very far away. So how does this happen? Let’s think! There must be some source to produce the energy, right? And know it, that source element is Hydrogen.

In the sun’s core, due to the immense gravitational force and high temperatures, Hydrogen atoms squeeze to form Helium and this is called Nuclear Fusion. During a fusion reaction, tremendous amounts of energy are released in the form of heat and light. By the time this energy reaches the surface, it would have cooled down to around 6000 degrees Kelvin. And this is the temperature that corresponds to what we see here on our planet. The light energy takes just 8 minutes 20 seconds to travel to earth from the surface. But the sun’s core is so dense that a photon of light can take 100,000 years from the center to get to the surface. Surprising, isn’t it? Be surprised. This article is written to get to know our nearest star well and maybe interest you in taking up solar research. Get ready! The sun contains a lot of mysteries for us to uncover.

Know what we might not know?!

We all know that Helium is one of the most abundant elements in the universe, but, an astonishing fact is that it was discovered on the sun before it was found on the earth. I was so curious to know the story, just like you all. Let me tell you what happened. In the year 1868, there lived a person named Pierre-Jules-César Janssen who was an astronomer belonging to France. He was intrigued about a yellow line in the sun’s spectrum while studying a total solar eclipse in Guntur, India. I know how pleasant it is to hear this! Spectroscopy is another beautiful area of study in astronomy and let’s learn more about that in upcoming blogs. Now let’s swim through history. On October 20 of the same year, an English astronomer named Sir Norman Lockyer realized that this yellow line, with a wavelength of 587.49 nanometers, could not be produced by any element known at the time. It was hypothesized that a new element on the sun was responsible for this mysterious yellow emission and he named it helium (After Greek Titan of the Sun, Helios). Though that was a tiny tale, I think it is great to know and now, let’s get back to the hero of our story, the sun.

What happens at the center of the sun?

The core is the center of the sun and comprises 25% of its radius. 99% of the sun’s energy is produced from the nuclear fusion reactions taking place in the core. The specific type of fusion that occurs is known as proton-proton fusion, which is explained through the below diagram.

A nuclear fusion reaction (Credits- University of Calgary Energy Education Website)

The sun’s various layers

The sun is just an ordinary star in the universe and 4.603 billion years old. Though the core and nuclear fusion is an important part of the sun, it has many more intricacies associated with it. Let’s look into the mysterious sun with our ever inquisitive minds. In simple terms, the sun has an interior and an atmosphere. The solar interior consists of the core, radiative zone, and the convective zone. The solar atmosphere consists of the photosphere, chromosphere, and the corona that extends to millions of kilometers in the outer space and is visible only during a solar eclipse. You can imagine the sun’s structure to be like a giant Rambutan of 1.392 million km in diameter. Ahhh! So huge it is. It seems it would take 1.3 million Earth-sized bodies to fill up the sun. Incredible! If you have not heard about a Rambutan, it is a delicious fruit that closely resembles lychee. I will include a picture of this analogy so that you will understand better.

The analogy between a rambutan and sun’s structure (Credits- TOI and Google Images)

The pictures are nice, isn’t it? I know. I used a Rambutan for the analogy just because I felt it’s outer hairy structure was kind of resembling the shape of the sun’s corona. Take a look at the picture of the corona taken during a solar eclipse. Okay, for now, just concentrate on the regions I mentioned before. Imagine the sun’s core to be the seed of the rambutan and the radiative and convective zone together to be the flesh of the fruit. The photosphere is the surface that is visible to us and you can imagine it like the skin of the fruit. The hairy structure can be thought of as the chromosphere and corona. I believe this would have helped you to picture the sun clearly.

Here I would like to tell a fun fact about the solar corona, the outermost layer of the sun. In fact, I want to tell you two important facts. First, the corona extends into millions of kilometers above the visible surface of the sun and gradually transforms into the solar wind that flows outward through our solar system. Second, the temperature in the corona is more than a million degrees, surprisingly much hotter than the temperature at the Sun’s surface. This is known as the coronal heating. The underlying cause is not yet clear and is an active research problem. It is something like a Nobel Prize-winning problem. If anyone is interested, you can try getting a Nobel Prize for solving it.

You would have definitely heard about NASA’s Parker Solar Probe. The mission is primarily aimed to understand the coronal heating problem and what accelerates the solar wind. NASA says that the Parker Solar Probe mission will revolutionize our understanding of the Sun and it will provide new data on solar activity and make critical contributions to our ability to forecast major space-weather events that impact life on Earth.

ISRO is also planning to launch India’s first mission to study the sun in January 2022. It is named Aditya – L1 and it will place a satellite in the halo orbit around the Lagrangian point 1 of the Sun-Earth system that has the advantage of continuously viewing the Sun without any occultation/ eclipses.

Image of the corona during a Solar Eclipse (Credits-NASA)

What do we observe through solar telescopes?

There are specialized telescopes through which we can observe several different features in the sun’s atmosphere, the cause for which is the sun’s magnetic field. The photospheric features include sunspots, faculae, and granules. And the chromospheric features include prominences, plages, and filaments. The coronal features include energetic events such as flares and CMEs. This is just to give you an overall idea, so just understand that the sun has features one can observe. For example, Sunspots are seen as dark spots on the sun when viewed through solar filters. We will see this using a picture, which is much more interesting. You can also observe sunspots by projecting an image of the Sun through a telescope or binoculars onto a white screen, like paper plates or walls. Try this out and have fun at home!

The features of the sun (Credits- NASA)

The magnetic activity and the solar cycle

Like the earth, the sun also generates a magnetic field. The solar cycle is the cyclic variations that the Sun’s magnetic field goes through approximately every 11 years. Now, this is another open research problem for solar physicists to work on, or maybe someone from you all one day. Why do you the solar cycle is roughly 11 years? If any ideas pop up, I would love to know in the comment section. Hopefully, it will be found out in our lifetimes. Remember? I said the sun holds a lot of mysteries for us. That’s indeed strange since we have been with the sun for so long and we have not yet understood it completely.

Let’s see what is happens in a solar cycle? The most prominent features of the sun are sunspots. It was because of the recording of the sunspots that the 11-year cycle was found out. During a solar cycle, the sunspots start occurring at a minimum rate and gradually increase to a maximum count and again gradually decreasing. It is also called as The Sunspot Cycle. It is predicted that by this year, Solar Cycle 25 would start.

(credit: SOHO (ESA & NASA))

Why do we study solar physics?

The sun is just a normal star in the universe. So what is the big deal in studying it? Since the sun is our only accessible nearest star, by understanding our sun, we can better understand other stars. The sun has important influences on earth. It drives our weather patterns, space weather, ocean currents, and climate, and also makes plant life possible through photosynthesis. So by mastering the processes that drive the sun, we are better equipped to understand our own planet too. Another practical implication is for predicting solar storms to safeguard our electrical grids and satellites in orbit. I leave this for my readers to reason out how solar storms affect the earth.

Search for the invisible discoveries in the sun when you find yourself running for shade during a sunny day. (A tip- Never try to look at the sun directly with your eyes. Use solar filters, telescopes, and the best option, research using Google. ) Have a great time researching!

I think that was quite a trip to learning about our star and it was awesome traveling with you people. Hold yourself to Spaceonova’s blog for amazing articles relating to space science.

Resources- NASA, ESA, Wikipedia, LiveScience

Further Reading-

[1] https://www.isro.gov.in/aditya-l1-first-indian-mission-to-study-sun

[2] http://parkersolarprobe.jhuapl.edu/The-Mission/index.php

[3] https://www.space.com/58-the-sun-formation-facts-and-characteristics.html

[4] https://phys.org/journals/solar-physics/

[5] https://www.sciencemag.org/news/2019/05/scientists-tackle-burning-question-when-will-our-quiet-sun-turn-violent

#Spaceonova #Astrophysics #Sun #SolarPhysics #SolarStructure #SolarCycle

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Gayathri

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