Solar system,  Milky Way

Definition and Components of Our Solar System

Definition and components of our solar system

The solar system is the planetary system composed of celestial elements held together with the Sun by gravity. The Sun is a G2-class main-sequence star 1.39 million kilometers in diameter, representing 99.86% of the solar system's mass.

The solar system is located in the Local Interstellar Cloud, located in the Local Bubble of Orion's arm, within the Milky Way. The Milky Way is between 150 and 230 thousand light-years in size and has between 100-400 billion stars.

In the space between these celestial bodies is interplanetary matter. The main component of the interplanetary medium is the solar wind, which is a stream of charged particles flowing from the Sun. 

Components of the Solar System

In addition to the Sun, the Solar System contains eight planets, five dwarf planets, more than one million known asteroids, 644 planet moons, dwarf planets, and asteroids, and 3,701 known comets. Most of these objects revolve around the Sun in orbits with slight inclinations relative to the ecliptic.

The most prominent elements orbiting the Sun move in the same virtual plane called the ecliptic plane.

1. the Sun: the Central Star of Our Solar System

The sun is the unique star in our planetary system and the solar energy source.

The sun contains by its attraction all the planets of the solar system that orbit around it and other bodies that belong to him.

It is a medium star but, due to its proximity, it is the only star that can be seen with the naked eye in its circular shape.

The Sun emits energy in the form of radiation from the nuclear fusion reactions of hydrogen atoms inside it. This energy is vital for Earth's life (heating the planet, allowing plants to photosynthesize, etc.)

After the Sun, the closest star is Proxima Centauri, a low-mass star located 4.2465 light-years.

2. Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune

The solar system includes:

  • Inner planets: Mercury, Venus, Earth, Mars.

  • Outer planets: Jupiter, Saturn, Uranus, Neptune

All the planets and most solar system elements rotate around the Sun in the same direction that our central star rotates (counterclockwise when viewed from the Sun's North Pole). However, the time they take to orbit the Sun is not the same: while the Earth's orbit is about one year, the orbit of Neptune takes 135 years.

Most planets revolve around their axis in the same direction as they revolve around the Sun, except Venus and Uranus.

Planets orbit the Sun following Kepler's laws. According to Kepler's laws, each object does not rotate in circular orbits, but on an ellipse, in one of whose foci is the Sun.

3. Satellites of Planets and Moons

Most of the planets in the solar system have their subordinate systems. Many are surrounded by satellites; some of them are larger than Mercury.

The four largest planets are gas giants. These planets also have rings, thin bands of tiny particles that rotate in very close orbits almost in unison.

4. Dwarf Planets

A dwarf planet is a spherical object that moves in a heliocentric orbit but has not cleared the surrounding space.

5. Other Small Bodies

The terms minor planet and planetoid refer to a classification, currently in disuse, that until 2006 included the bodies of the solar system

Small bodies of the solar system are grouped into:

  • Asteroid belt.

  • Trans-Neptunian objects and the Kuiper Belt.

  • Oort cloud.

Before 2006, there was the concept of the minor planet. This definition included the system solar bodies that, not being satellites or comets, turned out to be smaller than the "traditional" planets but more significant than meteoroids, commonly defined with a maximum size of 10 meters.

What Is the Origin of the Solar System?

According to modern thinking, the solar system was formed about 5 billion years ago due to the accumulation and compression by the gravity of a cloud of gas dust called the solar nebula.

Definition and components of our solar systemIn the compression process, the dimensions of the solar nebula decreased, and the rotation speed increased. As a result, most of the mass had been concentrated, and it began to heat up much more than the surrounding disk.

The compression speeds of the clouds parallel and perpendicular to the axis of rotation were different. It caused the flattening of the cloud and the formation of a characteristic protoplanetary disk and a hot, dense protostar in the center. The accretion of this disk formed the planets.

In 50 million years, the pressure and density of hydrogen in the center of the protostar became high enough to start a nuclear fusion reaction of hydrogen atoms.


Published: September 23, 2021
Last review: September 23, 2021