Universe: Characteristics and Organization

Key Concepts

• Universe

• Telescope

• Structure of sun

• Nuclear fusion

• Sunspot cycle

• Prominences

• Flares

Introduction

What is Universe? 

The universe is nothing but everything we can feel, touch, sense, measure, and detect. The universe includes planets, stars, galaxies, living things, dust, clouds, time, and even light. Before the origin of the universe, space, matter, and time did not exist. The universe is considered an endless space, and all living things, including human beings, belong to space. 

The scientific study of the universe is called astronomy. The scientist who studies the universe is known as an astronomer. 

Astronomers have made exciting discoveries such as stars, galaxies, planets, nebulas, etc., by observing the universe. By studying these objects (galaxies, nebula, planets etc.), astronomers were able to learn about the origin of Earth and the steps involved in the formation of the solar system and other objects present in the universe. 

We know that the universe contains billions of galaxies, and each contains millions of stars. The space between stars and galaxies is mostly empty; even places far away from stars and planets consist of scattered dust particles or a few hydrogen atoms per cubic centimeter. Space is covered with radiation such as light radiation, heat radiation, magnetic fields, and high energy particles such as cosmic rays. 

Characteristics of the Universe 

Cosmology is the study of the origin, characteristics, processes, and evolution of the universe. Astronomers studied and found out that the universe started almost 13.7 billion years ago in one massive explosion called the big bang, and since that time the universe is expanding. The universe is too large and the objects present in it are far away from each other, so a telescope is used to study far away objects. Nowadays, with scientific development, astronomers also use computers and mathematical models to study the universe. 

Organization of the Universe 

The solar system is the closest part of the universe to Earth. The solar system consists of the Sun, Earth, other planets, dwarf planets, asteroids, and comets. It (the solar system) is a part of the galaxy. Galaxy consists of stars, dust particles, and gas forced together by gravity. Milky way of galaxy is the galaxy in which the solar system is present. There are billions of galaxies present beyond the milky way galaxy. 

Measurement of distance in the Universe 

We know that the universe is very big, and the units of measurement on Earth are very small to show the distance between the various objects present in space. So to measure distance, astronomers usually use astronomical units. The astronomical unit (represented by AU) is defined as the average distance between Earth and the Sun, which is approximately 150 million Km. The speed of light is also used to measure distance. Light travels with the speed of 300,000km/s. Light travels 9.46×1012 km in one year.This distance is called as light year. Apart from the Sun, the closest star to Earth is 4.22 light years away. 

Observing Space :

We could see the world around us and make observations because of light. At night, we can see stars and other objects in space because these objects emit light. This visible light is nothing but a small amount of energy that comes from objects. Astronomers are able to learn more about the universe by studying other forms of energy. We know that planets do not emit light, but they reflect light coming from stars. 

Electromagnetic spectrum: 

Visible light is a form of energy and is a part of the electromagnetic spectrum. The electromagnetic spectrum is defined as all the wavelengths of electromagnetic radiation. Examples of electromagnetic radiation are light, radio, waves, and x-rays. 

Visible Electromagnetic Radiation :

We can see only radiation of wavelength present in the visible light range of the spectrum. Electromagnetic radiation with wavelengths shorter than the violet light or longer than the red-light cannot be seen by the human eye. 

Invisible Electromagnetic Radiation: 

In 1800, scientist William Herschel discovered infrared light, which means below the red. Infrared radiation has a longer wavelength than visible light. The ultraviolet electromagnetic radiation means beyond the violet. Gamma rays have the shortest wavelengths. 

The Sun – A Main Sequence Star  

Though the Sun is an average star and it is the largest object in the solar system. The Sun is around 1.4 million kilometers in diameter, that is about 109 times bigger than Earth and even 10 times bigger than Jupiter. Like all stars, the Sun is made up of hydrogen and helium. Nearly 70% of the Sun’s mass is hydrogen and around 28% is helium. The remaining 2% of the Sun’s mass is oxygen and carbon. The Sun comprises of around 99% of all the mass in the solar system. 

Structure of the Sun :

The Sun can be categorized into different layers—the core, the radiation zone, and the convective zone. The visible surface of the Sun that we see is called the photosphere. The photosphere layer emits light into space. The temperature of the photosphere is around 5,800 K. Outside of the photosphere, the Sun has an atmosphere that is separated into two layers. The inner layer of the atmosphere is called the chromosphere, and the outer layer is called the corona

The Core:

The core stretches from the center of the Sun to about 140,000 km from the center. Nuclear fusion takes place in the Sun’s core. It produces the energy that reaches Earth. The fusion reactions convert hydrogen nuclei into helium nuclei. The temperature in the core region is around 15 million K. The temperature is so high that atoms have been exposed of their electrons. Due to this, the core is a gas made of charged particles. The state of matter made of charged particles is a plasma. 

The core is the power generator in the Sun present in its center. The radius of the core is close to one fourth of that of the star. Inside the core, pressures and temperatures are high enough to make fusion. Fusion is a nuclear reactions where some nuclei merge to make others. Proton-proton cycle is the most important reaction that occurs within the core of the Sun. 

In the proton-proton chain reaction, hydrogen nuclei are converted to helium nuclei through a number of intermediates. This reaction generates high-energy photons (gamma rays) that move through the “radiative layer”  that is surrounding the core. This layer takes up 60% of the Sun’s radius.  

In the core region, the helium nuclei make up 62% of the mass and the remaining is still hydrogen. The radiative and convective layers have around 72% hydrogen, 26% helium, and 2% heavier elements by mass. The energy generated by fusion reaction is then transferred to the solar surface and produced as light or emitted as high-energy particles. 

By the time the energy reaches the surface of the Sun, temperature have come down to 6000ﹾK. This is a temperature that relates to the sunlight that we see. On average, the energy released from the hot surface, is close to 230 million watts per square meter.  

Nuclear fusion is the source of all the energy emitted by the Sun, does two things: 1. It converts hydrogen atom into helium (or in other words, creates helium nuclei from protons) and it transforms mass to energy. 

The mass-to-energy conversion is explained by Einstein’s equation:  

E = mc² 

OR 

Energy = mass × the square of the velocity of light. 

As the velocity of light is a very big number, this equation tells that lots of energy can be obtained from using up a small amount of mass. 

The energy produced by the prcoess of  nuclear fusion within the core of the Sun (or any other star) exerts an outward pressure. If not contained, such pressure can make an explosion. The internal pressure that keeps a star from exploding is the gravitational attraction of the gas mantle that surrounds the core (It is the majority of the volume of the Sun, and is very hot but does not burn away by itself). 

The outward pressure generated from the nuclear fusion reactions prevents the stars from collapsing. The inward pressure from gravitation prevents the stars from bursting. If the nuclear fusion reactions in the core turn out to be very weak, a star can collapse. Such collapse can provide new situations in a core that develop in new types of nuclear fusion reactions, as a result expansion follows. If the nuclear fusion reactions in the core turn out to be more strong, then a star can explode.  

The Radiation Zone:

Radiation zone is present above the core. It extends from around 140,000 km to about 500,000 km from the center. In this zone, temperatures are even so high that matter is in the plasma state. In the radiation zone, the energy generated by nuclear fusion is transferred from the core by electromagnetic radiation. The temperature of the radiation zone decreases with distance from the core from about 7 million K to about 2 million K at the peak of the radiation zone.  

The Convection Zone:

The convection zone is the Sun’s outer layer. In this zone, energy is transported from the top of the radiation zone to the surface by thermal convection. Columns of hot material create convection cells as they rise to the surface, cool, and then sink to the bottom of the convection zone. 

Photosphere:

At the top of the convection zone is the Sun’s photopsphere. The photosphere has a grainy appearance. The individual grains of photosphere are called granules and are normally around 1,000 km across. Granules are the tops of the convection cells. The bright regions are hot material that is rising and the dark regions are cooler material that is sinking.  

Sunspots :

Some regions of the Sun look darker than others. These darker regions of the Sun’s photosphere are called sunspots. These are cooler than surrounding areas. Temperatures in the dark center  region of sunspots can be 2,000ﹾK cooler than the surrounding granules. Sunspots are carried by the roatation of Sun. The movement of sunspots indicates that the Sun rotates faster at its equator than at its poles. Sunspots are produced by areas of strong magnetic fields that decrease the transport of energy to the surface by convection. 

Sunspots are not the permanent characteristics of the Sun. They appear and vanish over periods of days, weeks, or months. The number of sunspots changes in a relatively consistent pattern called the sunspot cycle, or solar activity cycle. Cycles of sunspot maximum occur around every 11 years, with periods of sunspot minimum appearing in between. At a sunspot minimum, sunspots occur at high latitudes. As the cycle continues, sunspot appear closer to the Sun’s equator. By the next minimum, they again come together at high latitudes. 

Prominences and Flares:

Strong magnetic fields linked with sunspots can cause huge bending columns of gas called prominences to erupt. Convection in the convection zone causes magnetized gases to flow upward in the direction of the photosphere. Sometimes the strength of magnetic field is great enough that magnetic field lines shoot out from the surface near a pair of sunspots and produce a prominence of solar material to loop from one spot to the other spot. Some prominences explode material from the Sun into space at speeds that ranges from 600 km/s to more than 1,000 km/s. Sometimes gases near a sunspot suddenly brighten, and gases shoot outward at high speed called solar flares. Temperatures in these flares can go up to 100 million K. Particles produced in a solar flare retain so much energy that the Sun’s magnetic field cannot keep them as it can hold prominences, and they explode into space. 

Summary

• The universe is nothing but everything we can feel, touch, sense, measure, and detect

• The universe includes planets, stars, galaxies, living things, dust clouds, time, and even light.

• The scientific study of the universe is called astronomy.

• The scientist who studies the universe is known as an astronomer.

• Cosmology is the study of the origin, characteristics, processes, and evolution of the universe. Galaxy is consists of stars, dust particles, and gas forced together by gravity.

• Milky way of galaxy is the galaxy in which the solar system is present.

• The electromagnetic spectrum is defined as all the wavelengths of electromagnetic radiation. The examples of electromagnetic radiation are light, radio, waves, and x-rays.

• A telescope is a device that collects electromagnetic radiations coming from the sky and focuses it for good quality observation.

• The Sun can be categorised into different layers—the core, the radiation zone, and the convective zone.

• The inner layer of the atmosphere is called the chromosphere, and the outer layer is called the corona.

• Proton-proton cycle is the most important reaction occur within the core of the Sun.

• The darker regions of the Sun’s photosphere are called sunspots.

• Strong magnetic fields linked with sunspots can cause huge bending columns of gas called prominences.

• A sudden increase in the Sun’s brightness is called a solar flare.