THE PLANETS AND THE SOLAR SYSTEM

The Planets and the Solar System

What is SOLAR SYSTEM?

• Our planetary system is named the "solar" system because our Sun is named Sol, after the Latin word for Sun, "solis," and anything related to the Sun we call "solar."

• Our planetary system is located in an outer spiral arm of the Milky Way galaxy.

•  The sun together with the group of celestial bodies that are held by its attraction and revolve around it also : a similar system centered on another star.

The Composition Of The Solar System

• It consists of our star, the Sun, and everything bound to it by gravity — the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, dwarf planets such as Pluto, dozens of moons and millions of asteroids, comets and meteoroids.

• There are more planets than stars in night sky. Most of the hundreds of billions of stars in our galaxy are thought to have planets of their own, and the Milky Way is but one of perhaps 100 billion galaxies in the universe.

• It gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly.

Multiple Choice

^{🌏How old is our Solar System?}

• 4.6 billion years

• 5000 years

• 300 million years

• 500 years

The Age of the Solar System

• Billions of years ago, in some forgotten corner of the Milky Way, a molecular cloud like many others collapsed to form new stars. One of them formed in relative isolation, collecting material in a protoplanetary disk around it, and eventually forming our Sun, the eight planets, and the rest of our Solar System. Today, scientists proclaim that the Solar System is 4.6 billion years old

Structure

• The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of mostly rocky asteroids, and four giant planets surrounded by the Kuiper belt of mostly icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four giant planets.^[25] Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune

The Planets

• Mercury – The smallest and fastest planet.

  Venus –It's thick atmosphere makes it the hottest planet in our solar system.

  Earth – The only planet in our solar system with liquid water on the surface.

  Mars – Mars was a wet and warm planet billions of years ago.

  Jupiter – The largest planet, its dark red spot is a storm larger than Earth.

  Saturn – It has the brightest, most massive and most complex ring system of any planet.

  Uranus – It is tipped on its axis by almost 90-degrees.

  Neptune – It was the first planet discovered through mathematical calculations.

Multiple Choice

As of today, How many planets are there in the Solar System?

• 8

• 9

Distances and scales

• The distance from Earth to the Sun is 1 astronomical unit [AU] (150,000,000 km; 93,000,000 mi). For comparison, the radius of the Sun is 0.0047 AU (700,000 km). Thus, the Sun occupies 0.00001% (10⁻⁵ %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10⁻⁶) that of the Sun. Jupiter, the largest planet, is 5.2 astronomical units (780,000,000 km) from the Sun and has a radius of 71,000 km (0.00047 AU), whereas the most distant planet, Neptune, is 30 AU (4.5×10⁹ km) from the Sun

Formation and evolution

• The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud.  This initial cloud was likely several light-years across and probably birthed several stars. As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars. As the region that would become the Solar System, known as the pre-solar nebula, collapsed, conservation of angular momentum caused it to rotate faster. 

Moons

• It is also known as natural satellites – orbit planets and asteroids in our solar system. Earth has one moon, and there are more than 200 moons in our solar system. Most of the major planets – all except Mercury and Venus – have moons. Pluto and some other dwarf planets, as well as many asteroids, also have small moons. Saturn and Jupiter have the most moons, with dozens orbiting each of the two giant planets.

Sun

• The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses), which comprises 99.86% of all the mass in the Solar System, produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium, making it a main-sequence star. This releases an enormous amount of energy, mostly radiated into space as electromagnetic radiation peaking in visible light.

  The Sun is a G2-type main-sequence star. Hotter main-sequence stars are more luminous. The Sun's temperature is intermediate between that of the hottest stars and that of the coolest stars.

Orbits

• The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using numerical models.

• The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury are very nearly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earth's orbit).

Asteroid belt

• Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of refractory rocky and metallic minerals, with some ice. They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), depending on different, somewhat arbitrary definitions.

THE SOLAR SYSTEM

THE PLANETS

THE SUN

THE ORBITS

THE ASTERIODS