Astronomy: Earth

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Table of Contents

  1. Basic Facts
  2. Why Earth is not a Sphere
  3. Surface Composition
  4. Atmosphere
  5. For Educators

Earth: The Facts

One post is not enough for Earth, after all, there are many subjects that attempt to describe it. However, I will do a brief overview of our planet in a similar fashion to that of the previous planets. Earth is 93 million miles away from the Sun(this is 1 AU), has a rotational period of 24 hours(one day), and a revolution period of 365.25 days(1 year) around the Sun. What makes our planet unique is that all the prerequisites are met that allow for life, such as having water and having organic compounds. We all know the Earth is round(with the exception of some) but it is not a sphere. When you think of round you probably think of a sphere and assume that the Earth is one, after all, it looks like one in every picture we have of it from space. However, it is called an oblate spheroid, which means two things. Oblate means stretched out, and this applies to Earth in that it is stretched at the Equator such that the poles are flattened. Spheroid means it is like a sphere, but is not exactly one, for Earth this is because rather than being smooth and round, it is quite bumpy. Once thought about, this is to be expected, because the Earth has been impacted by all sorts of extraterrestrial debris. Earth is oblate because of its rotation. Simply put, this rotation requires the particles to be at a larger distance at the Equator to stay in orbit. I have explained this in much detail in the next section. Finally, The Earth rotates about its axle tilted 24.5 degrees from the vertical. This is likely because of something impacting Earth. This something has been hypothesized to be a Mars sized object that hit Earth 4 million years ago and is also responsible for forming the Moon(this is the giant impact hypothesis).

The tilt of Earth

Why Is the Earth not a Sphere?

Unless you are interested in the physics of this question, I would recommend to skip this section, it is long. However, it can help you understand why the Earth bulges at the Equator if you do not want to just take this as fact.

This high speed rotation creates a centripetal force, which is proportional to the square of the angular velocity and the radius(distance from center). Without this force, the Earth would be a sphere, so let us take that as a starting point. Now the sphere starts spinning, and at a uniform angular velocity(it rotates at the same speed). The particles in the atmosphere at the north pole are really close to the axis of rotation(the line through the middle of the Earth that the planet rotates around) while the particles at the Equator are far away from this axis. This means two things for the particles at the Equator, and vice versa for the Poles; gravity is weaker on these particles and the rotate farther away from the axis(gravitational force is from the center of the earth and decreases as distance increases from the center). One thing is constant, however, these particles rotate at the same angular velocity whether at the poles or at the Equator.

We know that at the Equator, gravity is less. In order for these air particles to stay in orbit of Earth(and not get released), the centripetal force must be higher to account for this lessened gravity. Since angular velocity is constant, the only thing that can do this is an increase in radius. This means that at the Equator, the particles must be farther away from Earth in order for this centripetal force to be larger(this may sound counter intuitive but remember the centripetal force is directly proportional to radius). This is why there is a slight bulge at the Equator, making it oblate.

Surface of Earth

We all know of the surface of Earth as we live on it, so I will just give some of the important facts to know. I will make a full series on the Earth where you can read more about this. Since Earth is a terrestrial planet, it has a rocky surface, which is called the crust. This is broken into plates known as the tectonic plates. 71 percent of this crust is covered by the oceans, which is 360 million square kilometers. The surface on land is a granitic rock called granodiorite, which is similar to granite but has more quartz and feldspar. Meanwhile, ocean crust is basaltic, which is rock formed from lava.

Earth’s Atmosphere

I have already made a post on Earth’s atmosphere, so to learn about it, click this link! Once I have an Earth Science blog going, I will go in more detail on the atmosphere there also.

For Educators

Teaching about the Earth is no simple task, and probably should be done over many months. There is a lot to teach, so be creative! You have to teach about things like the orbit of the planet, the rock composition, and the atmosphere. The best way to do this is using hands-on activities, for example, bring in a bunch of different rocks and help students figure out how to identify them. Then relate these rocks to the crust and have students go outside and search for rocks and explore the dirt to see what composes it!

Thank you

Thank you for reading! Any questions feel free to contact me at vijaypbharti01@gmail.com!