Planet Earth explained in just 2639 words

The Earth

The Boundless three-dimensional extent in which objects and events have relative position and direction, that’s SPACE!

We live here! In space, but how? Why isn’t the space killing us? And why is that we aren’t getting fried by the dangerous cosmic rays? Not freezing too! There are just so many factors that can kill us, but what is it that kept us alive till now?

Ops looks like you got me! It’s our lovely planet, EARTH. Having an atmosphere that protects us from all the different vagaries that’s there. And yes, how can we even miss the location of Earth in the solar system, stands 3rd in the list of planets.

Located at a distance of 149.6 million km from the burning star in our solar system, “THE SUN”. Earth is the only life-supporting planet known to us.

Our position in the solar system ….

Each one of us has an address so that our friends, people we know, etc. can locate us from anywhere in the world, likewise, our Earth to has an address which tells its exact location in the cosmos (don’t ask who wants to locate Earth now).

When determining the position of Earth in the universe we take Earth as the center.

So, the address goes like this.

Earth,

Solar System,

Milky Way,

Local Group,

Virgo Super Cluster,

Observable Universe.     

Now for a more precise one!

Earth – you know it. 12,756.2 km.  

The Orbit of the moon – path traversed by the moon. Diameter 768,210 km.

Geospace – space dominated by Earth’s magnetic field and its magnetotail. 6,363,000 – 12,663,000 km.

Earth’s orbit – the orbit of the Earth relative to the sun. diameter, 299.2 million km.

Moons orbit around planet Earth

Inner solar system – includes the sun, the inner planets (Mercury, Venus, Earth, Mars) and the asteroid belt. 6.54 AU (astronomical unit: roughly the distance from Earth to the sun)

Outer solar system – includes outer planets (Jupiter, Saturn, Uranus, Neptune).60.14 AU.

Kuiper belt – the belt of icy objects surrounding the outer solar system. Includes dwarf planets like Pluto, Haumea, and Makemake. 96 AU.

Kuiper belt
WilyD at English Wikipedia [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

Heliosphere – maximum extent of the solar wind. 160 AU.

Scattered disc – a region containing scattered icy objects surrounding the Kuiper belt.195.3 AU.

Oort cloud – spherical shell containing over a trillion comets. Its existence is currently hypothetical. 100,000-200,000 AU.

Solar system – includes the sun and the entire planetary system. 1.23 pc (parsec: 1 parsec = 3.26 light-years or 30 trillion km)

Local interstellar cloud – an interstellar cloud of gas through which our sun and other stars travel. 9.2 pc.

Local bubble – a cavity in the interstellar medium in which our sun and other stars are currently traveling. 2.82 – 250 pc.

Gould belt – ring of stars in the Milky Way in which the Sun is currently traveling. 1,000 pc  

Orion arm – a spiral arm of the Milky Way in which the Sun is travelling. 3000 pc.

The Orbit of the solar system – the orbit of the solar system relative to the galactic center. Diameter, 17,200 pc  

Milky Way – our home galaxy. Comprising of 200 billion to 400 billion stars and filled with interstellar space. 30,000 pc. 

Milky Way subgroup – Milky Way and the satellite dwarf galaxies that are gravitationally bound to it. 840,500 pc.

Local group – a group of at least 54 galaxies of which the Milky Way is a part of. 3 Mpc. (Megaparsec: a distance of one million parsecs)

Local sheet – a group of galaxies Including the local group. 7 Mpc.

Virgo supercluster – the supercluster of which the local group is a part. 30 Mpc.  

Laniakea – a group connected with the superclusters of which the local group is a part. Comprises of roughly 300 to 500 galaxy groups and clusters. 160 Mpc.

Observable universe – comprises of at least 2 trillion galaxies. 28,500 Mpc.

observable universe
Observable universe
Credit: Andrew Z. Colvin

Universe – beyond the observable universe lies the unobservable universe. Unobservable since the light from the unobservable regions hasn’t reached Earth yet. Minimum 28,500 Mpc is possibly infinite.

Formation

Planet Earth has formed roughly at the same time as the Sun about 4.5 billion years ago.

The Solar system was formed from a giant nebula. A nebula contains gas, ice, and dust which spun fast and flattened into a disk. In early years Earth was bombarded with asteroids and comets.

Who named Planet Earth

Well, every language calls the Earth something different “prthvee” in Hindi,  “terra” in Portuguese, “dünya” in Turkish, and “aarde” in Dutch.

The Earth is the only planet whose name is not derived from Roman/Greek mythology.

The name Earth probably comes from the German word “erde” which means “soil”, “ground” or “land”.

Shape of Earth

Everyone must have come across this question at least once in their lifetime. What is the shape of the Earth?

Well, not long ago, people thought that Earth was flat like a coin (Some people still believe in Flat Earth Theory).

So, Earth is round then? No. Potato shaped? No.

Earth is a sphere, not a perfect sphere but very close to being a perfect sphere.

So, saying that Earth is a sphere is not wrong but if we are getting technical then it’s actually an oblate spheroid – a sphere with a bulge around the equator. The Earth has bulged at its equator because it’s rapidly rotating on its axis. The Earth’s diameter at the equator is 45 km (27 miles) more than its poles.

If the Earth is round like a Globe then how it is possible that we don’t fall off?

It is because the Earth’s gravity pulls everything towards itself. So, the people on the opposite side of the planet are also being pulled towards the center.

Orbit and Rotation

The Earth orbits the Sun at an average distance of 150 million km. Earth makes one rotation in 23.9 hours and one full orbit around the Sun in 365.25 days. The 0.25 day of every year is added as a leap year after every four years.

The Earth’s average orbit speed is 29.78 km/s (107,200 km/h) or 66,600 mph.

The axial tilt of Earth is 23.43 which is responsible for seasons on the planet. When the Northern hemisphere is tilted towards the Sun, it is winter in the north and summer in the south. The situation is reversed in six months.

earth's apehelion and perihelion

Average distance from the Sun: 92,956,050 miles (149,598,262 km)

Perihelion (closest approach to the Sun): 91,402,640 miles (147,098,291 km)
Aphelion (farthest distance from the Sun): 94,509,460 miles (152,098,233 km) (NASA)

Size and distance

Earth is the biggest of the four terrestrial planets. Earth’s radius is 3,959 miles (6,371 km) which is slightly bigger than Venus.

The Earth orbits the Sun at an average distance of 150 million km also known as the Astronomical Unit (AU).

Which is the closest planet to Earth?

The question is tricky because the planet that’s closest to the earth is always changing depending on where they are in their respective orbits.

When Venus is in the middle of the Sun and Earth, it is at its closest point to Earth. During this period, Venus would be the closest planet to Earth.

For Earth and Mars to be at their closest, both planets need to be on the same side of the Sun, Mars needs to be at its closest distance from the Sun (perihelion), and Earth needs to be at its farthest (aphelion).

There are times when Mercury is closer when both Mars and Venus are on the opposite side of the sun.

Atmosphere

Earth’s atmosphere is made of 78% Nitrogen, 20% Oxygen and other gases like Argon and Carbo dioxide.

Our Earth’s atmosphere is loaded with a gas which we can’t live without, Oxygen, which is essential for life to flourish.

Earth also has an Ozone (O3) layer which protects us from the Sun’s harmful radiations. Our atmosphere also protects us from meteors, most of which burn up in the atmosphere.

Gases like Carbon dioxide and Methane are responsible for keeping the planet warm by trapping the heat from the Sun: called Global Warming. Without global warming, Earth would have been much cooler than it is today.

Too much global warming is also not good for example extreme global warming has made planet Venus the hottest planet in the solar system with an average surface temperature of 480 degrees Celsius.

Magnetic field

Earth’s magnetic field is generated because of planets’ rapid spin and molten nickel-iron core. The process of generation of the magnetic field is called the Dynamo effect. Earth’s magnetic field protects us from solar storms and radiations.

When charged particles from the solar wind become trapped in Earth’s magnetic field, they collide with air molecules above the planet’s magnetic poles. The air molecules then begin to glow and cause aurorae (Northern/Southern lights). (NASA)

Earth's magnetic field illustration
Original bitmap from NASA. SVG rendering by Aaron Kaase. This SVG image was created by Medium69.Cette image SVG a été créée par Medium69. William Crochot [Public domain]

According to NASA, the magnetic field of Earth has weakened 10% since the 19th century.

The Earth’s magnetic field can flip completely, with North and South poles swapping places.

After the switch happens, the compass needles will point south instead of North. The most recent switch occurred approximately 700,000 years ago.

Surface

The total surface area of Earth is about 550 million km^2 (192 million sq. mi). Of this 70.8 % is below sea level and covered by ocean water.

Earth’s oceans have an average depth of 2.5 miles (4 km) and contain 97 % of the Earth’s water. Below the ocean surface lies much of planets volcanos, mountains, canyons and plateaus.

Hawaii’s Mauna Kea volcano is taller from base to summit than Mount Everest, but most of it is underwater. Earth’s longest mountain range is also underwater, at the bottom of the Arctic and Atlantic oceans. It is four times longer than the Andes, Rockies and Himalayas combined. (source: NASA)

Hawaii's mount kea, tallest mountain on earth
Hawaii’s Mauna Kea
I
mage by Adrian Malec from Pixabay

The remaining 29.2 % also have volcanos, plains, and mountains but it varies from place to place.

Almost 75% of the earth’s surface is covered by sedimentary rocks.

Internal structure

Similar to other terrestrial planets like Mercury, Mars, and Venus, Earth is made of three layers: core, mantle, and crust.

The Core is the innermost layer and is made of two layers: inner core and outer core.

The inner core is about 1600 miles (2600 km) in diameter and is mostly solid. It is responsible for the planet’s magnetic field which protects us from harmful solar winds.

The outer core is liquid and is 1,400 miles (2,250 km) in diameter.

In between crust and core lies the mantle, the thickest layer which is about 1,800 miles (2,900 km) thick. The mantle is highly viscous.

The crust is the uppermost layer and is the coolest layer. The thickness of the crust varies from 6 km (3.7 miles) under the oceans to 30-50 km (19-31 miles) for the continents.

Life on Earth

Earth is the only planet in the solar system where life, as we know, exists. The universe is very big so there is every chance that life may exist somewhere else in the universe but we just don’t know of it yet.

Earth has millions of species ranging from deepest oceans to a few miles into the atmosphere.

Perhaps the biggest factor why life exists on Earth might be the presence of liquid water.

The first single-celled life is thought to have come around 3500 million years ago. The earliest evidence of life on Earth comes from fossilized mats of cyanobacteria called Stromatolites in Greenland that are about 3.7 billion years old.

Evolution of life on planet Earth chart
Evolution of life on Earth

The first multicellular organism came around 1000 million years ago.

About 66 million years ago a large asteroid impact led to the extinction of dinosaurs and large reptiles. This led to the evolution of humans.

Moon

We all know Moon: the brightest thin in the night sky. Earth’s Moon has no particular name it’s just called MOON.

Planet Earth's moon
Image by Susan Cipriano from Pixabay

Moon is the fifth largest satellite in the solar system after Ganymede (Jupiter), Titan (Saturn), Callisto (Jupiter) and Io (Jupiter).

Moon is 2,159 miles (3,474 km) in diameter that is about one-fourth of Earth’s diameter.

The Moon is farther away from Earth then it appears. It is an average of 238,855 miles (384,400 km) away from Earth.

Earth’s Moon probably formed when a large Mars-sized body collided with Earth, ejecting a lot of material into the orbit. This debris later formed into Moon.

The gravitational attraction between Earth and Moon causes tides on Earth.

Moon is tidally locked: its rotation period is the same as the time it takes to orbit the Earth. As a result, we always see the same side of the Moon from the surface.

Movement of stars

Depending on where you are on the Earth, the stars seem to move differently in the night sky.

If we go towards the poles, we will see that the stars seem to move in circles around the sky. For example, the North Star or Polaris, since it is directly in line with Earth’s axis of spin, it appears as if still while other stars twirl around it.

Next, if we go towards the mid-latitudes then towards the pole, the stars seem to move in tight circles and towards the equator, the stars seem to take wider arcs,

Lastly on the equator if we see, stars will appear as traveling straight and parallel across the sky.

This is all because the Earth is a sphere (an oblate spheroid) and of course the centuries of astronomical observation have taught us that the stars don’t move around the Earth and that this very illusion is created due to the Earth’s rotation along its axis.

Past beliefs about the structure of the solar system

The Geocentric model or the Ptolemy system was a dominated model from the 4th century BCE until the 17th century CE. It gave the description of the universe with Earth at the center.

Ptolemy's model of the universe
Ptolemaic geocentric model
Photo by: Bartolomeu Velho

According to this model, the Sun, Moon, stars and all the other planets orbited around the Earth. This stayed as a predominant description of the cosmos in many civilizations, for example, those of Ptolemy and Aristotle.

But how did they come with such a conclusion?

Well, their observation was completely aided by naked eyes, since during that time the telescopes weren’t discovered.

All of their perspective about the cosmos was based on two observations:

1st – if you go to any corner or anywhere on Earth, you will still see the sun revolving around the Earth. Likewise, all the stars and all the planets seem to revolve around the Earth. Though all celestial bodies mentioned had their own specific motion, when viewed from Earth looked as if revolving around it.

2nd – from an Earth-bound perspective, the Earth seems to never move from its position, that is, it felt stationary.

Changing the past beliefs ….                               

Heliocentric solar system, an astronomical model which says the Earth and the planets revolve around the Sun, which is at the center of the solar system.

Historically the heliocentric model as opposed to the geocentric model. It was proposed as early as 3rd century BC by Aristarchus of Samos. But since his model was not proved mathematically, it attracted just a little attention.

It was not until the 16th century that a mathematical model of the heliocentric solar system was presented by a mathematician, astronomer and catholic cleric, Nicolas Copernicus which lead to the Copernican Revolution.

Heliocentric orbit of the solar system
Heliocentric model

The race of astronomical wonders had begun. In the coming century, elliptical orbits were introduced by Johannes Kepler.

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