**UNIQUE EARTH : PART - I**

Among the billions of planets Earth is completely distinct, unique and weird . It is the largest of the Terrestrial Planets & third planet from the Sun of our Solar System.
Technology working day-night to find planets like Earth , but how much the average person really know about the home planet Earth ? How much do we really know about the ground underneath of our feet? Though we've lived on Earth all of our life.

We were learnt in our childhood that a day is 24 hours, but the Earth doesn't take 24 hours to complete the rotation on its axis & actually takes 23 hours, 56 minutes & 4 seconds. Which is referred a Sidereal Day by astronomers. Now what about the 4 seconds ? You may think that the time would add up , day-by-day, and within a few months day would be night and night would be day.
Remember that each day, the Sun moves about 1° compared to the background stars - about the size of Moon in the sky. So, if we add up this little motion from the Sun that we see since the Earth is orbiting around it as well as the rotation on its axis, we get a total 24 hours. This is known as Solar Day - is the amount of the Sun takes to return to the same place in the sky.

We're probably aware that the Earth has only 1 Natural Satellite, sometimes this is not true. There're 2 additional steroids locked into co-orbital orbits with Earth , they are called 3753 Cruithne and 2002 AA29, which are part of asteroids known as Near-Earth-Objects (NEO) . The first one measures 5 km across and sometimes it's called Second Moon . Though it doesn't orbit the Earth it has a synchronised orbit with our planet. The 3753 Cruithne also has an orbit that looks like it's following the Earth* in orbit , but it's actually following its won distinct path around the Sun.
The second one is only 60 meters across and sometimes it's referred to the Third Moon of Earth . The 2002 AA29 makes a horseshoe orbit around the Earth that brings it close to the planet every 95 years . In about 600 years the steroid will appear to circle Earth in a quasu-satellite orbit. It might make a good target for a space exploration mission.

According to Chemistry, there're 118 number of elements possible on Earth. But the Earth mostly made of Iron, Oxygen, Silicon and Magnesium . If we could able to separate the Earth out into piles of materials, we would get 32.1% Iron, 30.1% Oxygen, 15.1% Silicon and 13.9% Magnesium. If we could actually get down and sampled the core of the Earth it would be 88% Iron. That means, most of the Iron located at the Earth’s core. And we'd find the 47% of Earth’s crust is Oxygen if we sampled it.