The Solar System

Planets
Ah yes, as I've said there are many planets throughout the universe, and there are some out there that is just far strange. The closest planet to us is probably Mars. The nearest heavenly body could be The Moon which is 384,000 km or 238,606 miles far from us. Anyway, there are 8 planets (9 if you count Pluto), simply Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (Pluto is already considered as a dwarf planet). The terrestrial planets or inner planets are Mercury, Venus, Earth and Mars. The outer planets or Jovian planets are Jupiter, Saturn, Uranus and Neptune, also these planets are called gas giants.

Mercury
Mercury is the nearest planet to the Sun, about 0.4 AU (astronomical unit, exactly 149597870700 meters, about 150 million kilometers, or 93 million miles). Its period of revolution is 87.969 or either 88 earth days, and its period of rotation is 176 earth days, which means you could probably have 2 birthdays every year in this planet. Even though it's the nearest planet to the Sun, it is not the hottest, yet the heat when day is scorchingly hot and the coldness when night is freezingly cold. The temperature at day measures 700 K (427 °C; 800 °F) and measures 100 K (−173 °C; −280 °F) at night. Mercury's surface experiences the greatest temperature variation of the planets in the Solar System, most notably because it has almost no atmosphere to retain heat,. The inner parts of this planet has 3 parts, simply the crust, the mantle, and the core. Its crust measures 100–300 km or 62-186 miles thick, the mantle measures 600 km or 372 miles thick, and the core measures 1,800 km or 1,118 miles in radius. Mercury has no natural satellites nor does Venus.

Venus
Venus is the second planet from the sun about 0.7 AU away from it. What's interesting about this is that it's the hottest planet, its period of revolution is shorter that it's rotation, and it rotates on the opposite direction or also called retrograde rotation. It is the hottest planet because it's atmosphere is so thick and is made out of large amounts of carbon dioxide (CO²) and only a small portion of the atmosphere contains nitrogen (N). This gas makes up 96.5% of the atmosphere and only 3.5% of nitrogen. The gas prevents the heat from the sun to escape back to space, and this effect is known as the "Greenhouse Effect", and in the future, this effect could most likely to happen on Earth too probably because we are destroying nature. Its revolution takes 224.65 days to complete an orbit, but its rotation takes 243 earth days to complete a day. A day in Venus is called Venusian day and it rotates on a clockwise direction called retrograde rotation. This planet also has no natural satellite like Mercury.

Earth
This is the planet we live. Also known as "The Blue Marble", because the planet is mostly composed of water, covering about 3/4 of the planet. In the next billion years, the planet will no longer exist due to the sun expanding enormously by "annihilating" by means of getting near, but despite that, the Earth might actually survive. Not much to be scared, because we'll be actually long gone way before the Sun swallows or let's go of Earth.

Solar System
The planets, Saturn, Moon, Earth, Jupiter, Mars, Venus, Mercury, Uranus and Neptune are in one system, the system is the Solar System. We live on the Earth, in the Solar system, the universe, the unlimited. The Solar System comprises the Sun which is the biggest heavenly body in this system we live, comprises the objects that orbit it, either directly or indirectly, while the remainder are significantly smaller objects, such as dwarf planets and small Solar System bodies (SSSBs) such as comets and asteroids. This system was born 4.6 billion years ago. Although that the Milky Way and Andromeda galaxy will eventually collide together in the next 4 billion years, the system would most likely survive the collision because stars are far away from each other.