What are Galaxies, the Solar System, the Stars and Planets

You live in a home; in a town; within a state, province or whatever; part of a country on planet Earth, which is part of the solar system; which is located in a branch of the Milky Way; which is part of a small cluster of 30 galaxies known as the Local Group. And beyond that is the rest of the Universe, which is home toan estimated ten million clusters similar or larger to the Local Group, some of which may contain between 100 and 1000 galaxies.

And how did all those things come about?

We already reviewed the theory behind the universe. Now let's jump to the galaxies that make up those clusters.

A galaxy is a vast system of stars, gas, dust, and dark matter held together by gravity. Here is a list of some of the things that can be found in a typical galaxy:

  • Stars: Galaxies are made up of billions of stars, ranging in size from tiny red dwarfs to huge blue giants. These stars emit light and heat, and are the building blocks of galaxies.
  • Gas: Galaxies contain large amounts of gas, mainly hydrogen and helium. This gas can be found in clouds or diffused regions throughout the galaxy. This gas can eventually become new stars.
  • Dust: In addition to gas, galaxies also contain dust, which is made up of tiny particles of carbon, silicon, and other elements. This dust can absorb and scatter light, making it difficult to see objects behind it. Like the gasses, dust can eventually becomes solid objects such as stars and planets.
  • Planets: They can be found orbiting stars within a galaxy or possibly floating alone. Planets can range in size from small rocky planets like Earth to gas giants like Jupiter.
  • Black Holes: Some galaxies contain black holes, which are incredibly dense objects that have such a strong gravitational pull that not even light can escape them.
  • Dark Matter: Although it cannot be observed directly, scientists believe that most galaxies contain large amounts of dark matter, which is a type of matter that does not interact with light or other forms of radiation electromagnetic.
  • Nebulae: Nebulae are clouds of gas and dust inside galaxies. They can be the birthplace of new stars or the remains of dying stars.
  • Magnetic Fields: Many galaxies have magnetic fields, which can shape and influence the behavior of gas and dust within the galaxy.
  • Cosmic Rays: Cosmic rays are high-energy particles that can be found throughout the galaxy. They are believed to be produced by supernovae and other energetic events.

The current leading theory of how galaxies are created is through a process known as hierarchical clustering. According to this theory, galaxies form from small fluctuations in the density of matter in the early universe. These fluctuations are thought to have arisen from quantum fluctuations in the very early universe, which were amplified by inflation, a period of rapid expansion that occurred shortly after the Big Bang.

Over time, gravity caused these density fluctuations to grow and clump together, forming small clumps of matter. These groups then merged to form larger structures, eventually giving rise to the first galaxies.

As galaxies continued to form and evolve, their growth was influenced by a number of factors, including the interaction between dark matter and normal matter, the formation of supermassive black holes at their centers, and interactions between the galaxies themselves.

Our Galaxy: The Milky Way

To better understand galaxies, let's review our own; the milky way Followed by our Solar System and the different objects (the sun, planets, etc) within the system.

The Milky Way is a barred spiral galaxy that contains our solar system. It is a vast system of stars, gas, dust, and dark matter that is held together by gravity. The galaxy has a diameter of approximately 1,000,000,000,000,000,000 km (about 100,000 light years or about 30 kpc) across, and contains about 100-500 billion stars.

The Milky Way formed about 13.6 billion years ago, shortly after the Big Bang. It is believed to have formed from the merger of smaller galaxies and the accumulation of gas and dust. The exact process of formation of the Milky Way is not yet fully understood, but astronomers continue to study the galaxy to better understand its history and evolution.

The Milky Way is home to a wide variety of objects and phenomena, including stars, planets, nebulae, black holes, globular clusters, spiral arms, magnetic fields, and dark matter. The galaxy has a strong magnetic field that is thought to be responsible for shaping its structure, and it is surrounded by a halo of hot gas.

Our solar system is located in the spiral arm of the Milky Way, known as the Orion Arm. From our vantage point on Earth, we can see the Milky Way as a faint band of light stretching across the night sky. However, our view of the galaxy is often obstructed by gas, dust, and other objects within the galaxy.

Overall, the Milky Way is a fascinating and complex system that continues to captivate astronomers and scientists as they work to unravel the mysteries of our galaxy and the universe as a whole.

Our Galactic Neighborhood The Solar System

The Solar System is a planetary system consisting of the Sun and all celestial objects that are attached to it by gravity, including planets, dwarf planets, moons, asteroids, comets, and other small bodies.

The Sun is the central and most massive object in the Solar System, comprising more than 99% of its total mass. It is a G2 spectral type star, which means that it emits light mainly in the yellow-green part of the electromagnetic spectrum. The Sun is the source of energy for all life on Earth, and its light and heat are responsible for driving Earth's weather and climate.

The eight planets in the Solar System, in order of distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The four innermost planets, Mercury, Venus, Earth, and Mars, are known as terrestrial planets because they are small, rocky, and have relatively high densities. The four outer planets, Jupiter, Saturn, Uranus, and Neptune, are known as gas giants because they are much larger and have much lower densities than the terrestrial planets.

The Solar System also contains several dwarf planets, including Pluto, Ceres, Haumea, Makemake, and Eris. The dwarf planets are similar in size to some of the largest moons in the Solar System and are smaller than all eight planets. They have not cleared their orbits of other debris, as the eight planets have.

The Solar System contains numerous moons, including Earth's Moon, which is the fifth largest moon in the Solar System. Jupiter and Saturn have the most moons, with more than 70 each. Some moons are small and irregular in shape, while others are large and spherical.

The Solar System also contains countless asteroids and comets, which are remnants of the early days of the Solar System. Asteroids are small rocky bodies that orbit the Sun, while comets are icy bodies that originate from the outer reaches of the Solar System and have a characteristic coma and tail when approaching the Sun.

Overall, the Solar System is a fascinating and complex system of celestial bodies that scientists continue to study to better understand the history and evolution of our planetary system and the universe as a whole.

James Webb cosmic cliffs

The stars: especially our sun

Stars are massive, luminous balls of gas held together by their own gravity. They are powered by nuclear fusion, a process in which atomic nuclei combine to form heavier nuclei, releasing vast amounts of energy in the process.

Our sun is just one of several different types of stars that can be found in galaxies and the universe. Stars come in a variety of types, sizes, and colors. These are the different types of stars:

  • Red dwarfs: are the smallest and most common type of star in the universe. They have low mass and low temperature, and emit mainly red light.
  • Yellow Dwarfs: These are stars that are similar in size and temperature to the Sun. They emit mostly yellow light and are often referred to as G-type stars.
  • Blue Giants: These are very large and very hot stars that emit mainly blue light. They are often referred to as O-type stars and are among the brightest stars in the universe.
  • Red Giants: These are stars that have used up most of their hydrogen fuel and have expanded to several times their original size. They emit mainly red light and are often referred to as M-type stars.
  • White Dwarfs: These are the remnants of low to medium mass stars that have exhausted their nuclear fuel. They are very dense and hot and emit mainly white light.
  • Neutron stars: These are the remnants of high-mass stars that have undergone a supernova explosion. They are incredibly dense and emit mainly X-rays and other high-energy radiation.
  • Black Holes: These are objects that have collapsed to a point of infinite density, called a singularity. They are so dense that nothing, not even light, can escape their gravitational pull.

Our Sun is a typical star, classified as a G-type main sequence star. It is made up of about 70% hydrogen and 28% helium, with the remaining 2% consisting of other elements such as carbon, nitrogen and Oxigen.

The Sun's energy is generated in its core, where temperatures and pressures are high enough to initiate nuclear fusion reactions. In the nucleus, hydrogen nuclei fuse to form helium nuclei, releasing energy in the process. This process, known as the proton-proton chain, is the main source of energy production on the Sun.

The energy released by nuclear fusion in the Sun's core travels outward through the layers of the Sun's interior, eventually reaching the surface, where it is radiated into space as visible light and other forms of electromagnetic radiation. The energy released by the fusion reactions of the Sun is what allows life to exist on Earth, providing heat and light for photosynthesis and other vital processes.

The Sun's life cycle is expected to last about 10 billion years. It is currently in the middle of its main sequence stage, where it is fusing hydrogen into helium in its core. As the Sun uses up its hydrogen fuel, it will begin to evolve and expand, eventually becoming a red giant before collapsing into a white dwarf.

Overall, stars are fascinating objects that continue to captivate scientists and astronomers as they seek to understand the complex processes that drive these incredible objects.

The planets: especially the earth

Planets are large, spherical objects that orbit a star and do not produce their own light. They are typically made of rock, metal, or gas and are held in their orbits by the gravitational pull of the star they orbit.

Planets form through a process known as accretion. This process begins with a cloud of gas and dust, known as a protoplanetary disk, surrounding a young star. Within this disk, dust and gas particles begin to clump together due to gravitational attraction. As these clumps grow, they begin to attract other clumps, eventually forming planetesimals, small rocky bodies that are the building blocks of planets.

Over time, these planetesimals continue to collide and merge with each other, growing in size and eventually becoming protoplanets. Protoplanets are larger than planetesimals and have enough mass to gravitationally pull in even more material. As protoplanets continue to grow, they may begin to draw in gas from the surrounding protoplanetary disk and eventually form gas giants like Jupiter and Saturn.

Once a protoplanet has accumulated enough mass, its gravity becomes strong enough to pull in more material from its surrounding area. This process, known as accretion, continues until the protoplanet has cleared its orbit of all other objects, becoming a planet. The planet formation process can take millions or billions of years, depending on the size and location of the protoplanet.

There are eight planets in our Solar System, listed here in order from the Sun:

  • Mercury: is the smallest planet in the Solar System and the closest to the Sun. It has a rocky surface, full of craters and no atmosphere.
  • Venus: is the second planet from the Sun and is similar in size and composition to Earth. It has a thick, toxic atmosphere that traps heat, making it the hottest planet in the Solar System.
  • Earth: is the third planet from the Sun and is the only known planet with liquid water and a stable climate. It has a solid surface and a thin atmosphere that supports life.
  • Mars: is the fourth planet from the Sun and is known as the "Red Planet" due to its reddish appearance in the sky. It has a thin atmosphere and a rocky, desert-like surface.
  • Jupiter: is the largest planet in the Solar System and the fifth planet from the Sun. It is a gas giant, with no solid surface and a thick atmosphere containing colorful cloud bands and swirling storms.
  • Saturn: is the sixth planet from the Sun and is also a gas giant. It is known for its spectacular rings, made up of countless ice particles.
  • Uranus is the seventh planet from the Sun and is an ice giant, with a solid core surrounded by a thick layer of icy gas.
  • Neptune: is the eighth planet from the Sun and is also an ice giant. It has a deep blue color and is known for its strong winds and large storms.

In addition to these eight planets, there are also five recognized dwarf planets in the Solar System: Ceres, Pluto, Haumea, Makemake, and Eris. These objects are smaller than planets and are generally found in the outer Solar System beyond Neptune.

In general, planet formation is a complex process that requires the right conditions, including a protoplanetary disk, gravity, and time. Understanding how planets form can provide valuable information about the formation and evolution of our own Solar System and other planetary systems in the universe.

Regarding Pluto

Pluto is no longer considered a planet because in 2006, the International Astronomical Union (IAU) redefined the criteria for what constitutes a planet. Under the new definition, a planet must:

  • orbit the sun
  • Be massive enough to have an almost round shape.
  • Have cleared its orbit of other debris and objects.

Although Pluto meets the first two criteria, it does not meet the third. Pluto is part of a region of the Solar System known as the Kuiper Belt, which contains many other small objects and debris. Therefore, the IAU reclassified Pluto as a "dwarf planet", which is a separate category of celestial objects that meet the first two criteria but not the third.

The decision to reclassify Pluto was controversial and met with some resistance from the public and some scientists. However, it was done in an effort to create a more precise and scientifically accurate classification system for objects in our Solar System.

And that's a breakdown of galaxies, solar systems, stars, and planets. Astronomy is awesome.

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