In the last episode, we talked about why Earth is habitable. Today, we will continue exploring Earth and Moon.
First, we will talk about Earth. Earth is a beautiful blue planet with a relatively huge moon. Moon has a diameter of 27% the Earth’s and it is the relatively largest moon in the 8 planets in the Solar System! We will talk about Moon later.
Earth’s dimensions
Earth is a terrestrial planet with a diameter of 12,742 km, which is about 302 marathons. It has the mass of 1 Earth mass, which is about 5,972,190,000,000,000,000,000,000 kilograms. It is also the densest planet in the Solar System, its density is 5.51 times of water. Its g-force is 1g, which is about 9.8 m/second squared. It is the most massive, the densest and the largest terrestrial planet in the Solar System.
Earth’s profile
Earth’s surface is covered in water. It has 71% of water while the others are land. It has 7 continents: North America, South America, Africa, Europe, Oceania, Asia and Antarctica. Earth’s tectonic plates are constantly moving and theoretically, there was a large continent called Pangea, which consists of all the land. But after that, Pangea broke apart and formed 7 continents. There are 8.7 million species known as of 2011, and there is a lot more to be discovered. Earth’s highest mountain from land is Mount Everest, which its peak is 8,848 metres from sea level. The deepest trench on Earth is Mariana Trench, which its depth is 11,000 metres from the sea level.
The atmosphere consists of 78% nitrogen, 21% oxygen and 1% other elements and compounds.
Earth’s rotation and revolution
Earth spins on its axis with a tilt of 23.5 degrees which makes seasons. When the northern hemisphere is in winter, the southern hemisphere is in summer, and vice versa half a year later. It takes 24 hours for it to rotate and 365.25 days to orbit around the Sun. The additional day for calendars every four years is called leap days. (note: 1700,1800,1900 etc. is not a leap year due to the small variations of calendars, but 1600 and 2000 are.)
Earth’s orbit is actually elliptical, with the perihelion being on early January, and the aphelion being on early July.
Earth is the only celestial body known to harbor life. This is answered in the last episode.
Moon’s profile
Moon is the only natural satellite and the largest object in orbit around Earth. It is the fifth-largest moon in the Solar System, being one eighty-first the mass of Earth and has one fifty-first the volume of Earth. It is the closest celestial body to Earth, only 384,400 kilometres away and it is also the closest natural satellite to the Sun, because the closer planets, Venus and Mercury have no moons.
Unlike Earth, Moon has no atmosphere. Instead, it has an exosphere. Its exosphere is so thin that it is a molecular cloud like a nebula surrounding it, and sound waves cannot travel there because there is no contact between molecules there.
Moon is the only place humans have set foot on except Earth, and it has been only visited by 12 people.
Moon’s rotation and revolution
One side of Moon always faces the Earth because Earth tidally locked it. That is quite common for other moons and exoplanets. It takes 27.3 days for Moon to orbit Earth once.
Moon phases occur because the relative position of the Sun, Earth and Moon changes over time when Moon orbit around Earth. A moon phase cycle is about 30 days. The approximately 2.7-day difference is because Earth has moved a little, approximately one twelfth in its orbit.
Moon’s Orbit is tilted about 5 degrees to the Earth’s orbit, so we don’t see solar or lunar eclipses every month. Moon’s Orbit is dynamic and sometimes passes through Earth’s orbit at a new moon or a full moon. A solar eclipse or lunar eclipse occurs.
Solar Eclipse and Lunar Eclipse
When the Moon is in the middle of Earth and Sun and they form a straight line, Moon will obscure Sun, either partially or completely. If Moon is in its apogee during a solar eclipse, it can only obscure part of Sun, sometimes leaving a ring-like ‘object’ in the sky.
When the Moon enters the shadow of Earth, a lunar eclipse will happen. There are no lunar annular eclipse because Earth is larger than Moon.
