Astronomy Subject

1. Lesson 2.3: Earth's
Atmosphere

2. Learning Outcomes
In this lesson, you are expected to do the following;
◦ Determine the different atmospheric layers of the Earth.
◦ Differentiate each layer of Earth's atmosphere.
◦ Appreciate the importance of each layer.

4. Troposphere
The troposphere is the layer of the atmosphere nearest to the
surface of the Earth.The clouds are seen in this layer and this is
where the weather occurs. It is also considered as the wettest layer
because of the moisture that it holds.The troposphere span is from
the surface of the Earth to approximately 10 km (6.2 miles or about
33,000 feet).The height of the troposphere is dependent on the
latitude (It is in the lower position in North and South Poles but the
highest position in the equatorial part) and by season (during
winter is at the lowest and the highest during summer).
The air temperature of the troposphere decreases as you move from
the bottom to the top. It is warm if you are near the surface and gets
colder as you move up. It is also the same case with air pressure and
density; as you, the altitude increases, it decreases.That's why the
cabins of jets are always pressurized.The next layer after the
troposphere is the stratosphere. In between them is what we called
the" tropopause."

5. Stratosphere
The stratosphere's bottom part is situated at about 10 km (6.2 miles or
about 33,000 feet) above the surface. The topmost part of it is
approximately at an altitude of 50 km (31 miles). Same with the
troposphere, its height is dependent on the season that occurs annually.
During wintertime, the lowest portion of the stratosphere is about 20 km
(12 miles or 65,000 feet) near the equator, while 7 km (4 miles or 23,000
feet) at Northern and southern poles.The boundary of the stratosphere
and mesosphere is what we called "stratopause."
Ozone (O3) is abundant in this layer of the atmosphere that responsible
for absorbing energy from the sun that is composed of ultraviolet rays.
When you are in the stratosphere, the temperature increases as you go
upward, unlike that of the troposphere that is inversely proportional.
Because of these changes in temperature in each layer, there is a process
of convection to stabilize the temperature.

6. Stratosphere
The stratosphere is called the "jet stream" because of the thin air in its
lower portion that makes it stable compared to that of the
troposphere. It avoids turbulence for a safe and stable flight
Unlike the troposphere, the stratosphere is dry because it lacks
moisture. It is the reason why fewer clouds are formed in this layer; it
is usually formed in the humid part of the troposphere.
Polar stratospheric clouds (PSCs) that are situated on the lowest part
of the stratosphere in the polar region during winter is an exemption.
These clouds are at about 15 to 25 km (9.3 to 15.5 miles). It is formed
when the temperature is below -78° C. It helps to create the holes in
the ozone because of the chemical reactions that happen in its
formation; it is also known as nacreous clouds.

7. Mesosphere
The mesosphere is the third layer of the atmosphere, starting from the surface. It is in
between the stratosphere and thermosphere. It has a range of approximately 50 to 80 km
(31 to 53 miles) above the surface of our planet. Same with the troposphere, the
temperature of the mesosphere decreases with as the altitude increases.
The coldest temperatures recorded on Earth's atmospheric layers, approximately -90° C (-
130° F), is found in the mesosphere
The demarcation line between the mesosphere and thermosphere is known as
"mesopause."
This layer of the atmosphere is hard to study; that is why only a few data is available about
the mesosphere.The hot air balloons cannot reach through this layer. Some satellites are
launched at this layer, but they still can't fully study the composition of each layer.
When meteors enter this layer of the Earth, they are usually vaporized, and that's the
reason why this layer is composed of iron and other metal elements.

8. Thermosphere
The thermosphere is the fourth layer of the atmosphere, starting from the surface of
the planet. It is in between the mesosphere and the exosphere. It ranges
approximately at about 80 km to 640km and 1,000 km (311 to 621 miles). Above the
surface, its boundary to the exosphere is what we called as the "thermopause."
This layer is usually thought of as the starting point of the outer space because of its
low air density. Space shuttles and space crafts are usually found at this layer of the
atmosphere.
The collision of gas particles happens in the thermosphere, wherein they break and
become separated depending on the chemical that it contains. Photons of ultraviolet
rays and X-rays also splits in this layer of the atmosphere.The air in the uppermost
part of the thermosphere contains atoms of oxygen, nitrogen, and helium.

9. Thermosphere
When X-rays and ultraviolet rays traveled in this layer, most of them are being
absorbed. In the case that the sun releases an enormous amount of radiations and
electromagnetic waves, the thermosphere expands. Because of this, the altitude of the
thermopause changes. Because of this, the height of the top of the thermosphere (the
thermopause) varies.The thermopause is usually located at a height of approximately
500 km and 1,000 km.
Finally, the Northern and Southern lights, also known as the aurora, happens in the
thermosphere.When charged particles from outer space impacts with other atoms
and molecules.When this happens, it excites the charged particles and atoms,
creating an enormous amount of energy that emits photons of that which we can see
in the night sky called auroral display.

10. Exosphere
The exosphere is the outermost layer of the atmosphere. It extends from the
thermosphere up to outer space.The air in the exosphere is a thousand times thinner
than the other layers that are comparable to that of space.
Not all scientists and space experts consider the exosphere as one layer of the
atmosphere.They believe that the thermosphere is the last layer of the Earth's
atmosphere and the exosphere is a part of space.The reason is because of the
exosphere air density that very low and thin.There is no clear demarcation on which
is the boundary of the exosphere as it slowly fades away as you go higher.
The outermost limit of the exosphere puts around 190,000 km (120,000 miles). At this
separation, radiation pressure from the sun applies more power to hydrogen particles
than the draw of Earth's gravity

11. Exosphere
The exosphere is the outermost layer of the atmosphere. It extends from the
thermosphere up to outer space.The air in the exosphere is a thousand times thinner
than the other layers that are comparable to that of space.
Not all scientists and space experts consider the exosphere as one layer of the
atmosphere.They believe that the thermosphere is the last layer of the Earth's
atmosphere and the exosphere is a part of space.The reason is because of the
exosphere air density that very low and thin.There is no clear demarcation on which
is the boundary of the exosphere as it slowly fades away as you go higher.
The outermost limit of the exosphere puts around 190,000 km (120,000 miles). At this
separation, radiation pressure from the sun applies more power to hydrogen particles
than the draw of Earth's gravity

12. Exosphere
Underneath the exosphere, particles of gases in the atmosphere continually collide
into one another. Since the air in the exosphere is thin, it is unlikely and rare to
happen.
Although the exosphere is, in fact, part of Earth's atmosphere, from numerous points
of view, it is a part of space. Numerous satellites, including the International Space
Station (ISS), circle inside the exosphere or beneath. For instance, the normal height
of the ISS is around 330 km (205 miles), setting it in the thermosphere beneath the
exosphere! Even though the air density is incredibly thin in the thermosphere and
exosphere, there is still enough air to cause a slight amount of force on satellites that
circle inside these layers.

13. Thank you! ☺