Earth and Space - The Solar System and Planets

The Solar System consists of the Sun, eight planets, their moons, and smaller objects like asteroids and comets. The planets in order from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The four inner planets ($Mercury, Venus, Earth, Mars$) are terrestrial planets, meaning they are rocky and relatively small.

The four outer planets ($Jupiter, Saturn, Uranus, Neptune$) are gas giants or ice giants, composed primarily of hydrogen ($H_2$), helium ($He$), and ices like water ($H_2O$) and methane ($CH_4$).

Gravity is the force that keeps planets in orbit around the Sun. The gravitational pull depends on the mass ($m$) of the objects and the distance ($r$) between them.

Mass is the amount of matter in an object (measured in $kg$), while Weight is the force of gravity acting on that mass (measured in $N$). The gravitational field strength ($g$) on Earth is approximately $9.8 \text{ N/kg}$, while on the Moon it is approximately $1.6 \text{ N/kg}$.

Distances in the solar system are often measured in Astronomical Units ($AU$), where $1 \text{ AU} \approx 1.5 \times 10^8 \text{ km}$, representing the average distance from the Earth to the Sun.