Earth-Sun Relations Seasons Daily Temperature Variations
Earth-Sun Relations
The sun is the driving force in our Solar System. Upon a closer examination of the Earth's orbital pattern around the sun, we see that the subtle elliptical mechanics involved play a small role in determining the Earth's climate, however, the rotation of the Earth on its tilted axis plays a huge role in determining our climate.
The Earth, as well as the rest of the planets, follows an elliptical path around the sun. Johannes Kepler (1571-1630) pioneered laws of elliptical motion. The Earth makes one revolution around the sun every 365.25 days, or, one y ear.
Kepler's 3 laws are stated as follows:
The degree of non-roundness of an ellipse is termed eccentricity. The eccentricity is the ratio of the semiminor axis to the semimajor axis of an ellipse.
Due to the Earth's elliptical motion about the sun, during different times of the year, the Earth is at different distances from the sun. When the Earth is at its closest point in its orbit, it is at perhelion. When its at its furthest point, it's at aphelion. As we will soon discover, seasons are not caused by differing distances of the sun from the Earth.
It is interesting to note that up until the 1600s, the Earth was believed to be at the center of the Solar System and the planets and the sun were believed to revolve around the Earth. This point of view is referred to as geocentric. Also, up until the 1500s, the Earth was believed to be flat by most people. However, in ancient Greece long before the 1500s, Pythagoras (who formulated the pythagereon theorem), did an experiment suggesting the Earth was round. But people probably thought he was crazy. I'll go over the experiment in lecture. Explorers such as Christopher Columbus and Ferdinand Magellan proved beyond a doubt that the Earth was round.
Gravity
Gravity is the attraction that is present between any two objects in the universe. Gravity is also what keeps objects in motion around other objects (such as the Moon around the Earth and the Earth around the sun). A balance of a gravitational force directed inward and a centripetal force directed outward keeps an object a constant distance away from the object it is revolving about.
Centripetal force
is a force that is developed when an object moves in a curved path.A force is the product of a mass times an acceleration. An acceleration is a change in velocity over a change in time.
Earth's Rotation
In addition to revolving around the sun, the Earth rotates on its axis and the axis of the Earth's rotation is tilted at an angle of about 23.5 degrees. Earth's rotational period is 23 hours 56 minutes and 4 seconds. Our clock however is set a ccording to a 24 hour day. Every four years, the 3 minutes and 52 seconds left over from each day adds up to one full day. To adjust our calendars for this imperfection, we have Leap Year.
If you have ever spun a top on a table or other flat surface, you notice that at certain rotational speeds, the axis of rotation of the top will wobble. The same effect occurs with the Earth. The result is that during different times of the year, dif ferent parts of the Earth face the sun and other parts of the Earth face away from the Earth. As a result, different parts of the Earth receive varying amounts of insolation - (Incoming Solar Radiation.
During the Summer in the northern hemisphere, the northern hemisphere is facing toward the sun and as a result is getting more direct radiation. During the Winter in the northern hemisphere, the northern hemisphere is facing away from th e sun and as a result is getting less direct radiation. The seasons are switched in the northern hemisphere and southern hemisphere. In other words, when its Summer in the northern hemisphere, its Winter in the southern hemisphere and vice-versa.
Because the Earth is a sphere, sunlight arrives at different parts of the planet at different angles. The closer to perpendicular (90 degrees) that the sunŐs rays arrive, the stronger the sunŐs rays will be at the location they are striking. As will be illustrated in class, in equatorial regions, the sun's rays are much more direct and closer to perpendicular than in the polar regions. This is why these latitudes are so much warmer.In the northern hemisphere, the period between Summer and Winter is called Autumn or Fall. The period between Winter and Summer is called Spring. The first days of the seasons are determined by the locations on Earth where the su nŐs rays are directly overhead.
| First day of: (in Northern Hemisphere) | Sun directly overhead |
|---|---|
| Summer | 23.5 degrees N |
| Autumn (Fall) | Equator |
| Winter | 23.5 degrees S |
| Spring | Equator |
The first day of Summer and Winter are referred to as the Summer Solstice and Winter Solstice respectively. The first day of Autumn and Spring are referred to as the Autumnal Equinox and the Vernal Equinox respectively.
There is a lag in time between the hottest day of the year and the Summer Solstice. In the northern hemisphere, typically the hottest day of the year climatologically is sometime in August. The coldest day of the year climatologically is in early Feb ruary well after the Winter Solstice.
Tidal Forces
Tides in the ocean are the result of the Moon's gravitational influence on the Earth. Each day at every location on Earth, there is a high tide and a low tide. High tide is when the Earth is facing the Moon and a point on the Earth will be closest to the moon whereas low tide would be when a point on Earth is facing away from the Moon.
Gravitational force is dependent on distance according to the formula F = GM1M2/r^2 (more about this in lecture). All masses in the universe are under the influence of all other masses according to the above formula.
Solar relation concepts
Solar noon refers to the spot on Earth where the sun's rays are directly overhead. Solar elevation refers to the angular distance off of the horizon that the sun can be found.
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