# Earth and sun relationship

### Sun Earth Relationship

I Earth-Sun Relations: Figure 1 below shows that the orbit of the Earth about the sun is not circular. The path is elongated or ellipitcal. This means that the. The Earth-Sun Relationship. A look at the Earth-Sun system provides important insight into current environmental phenomena. Since the beginning of the Earth's . Sun Earth Relationship. The earth receives almost all its energy from the Sun"s radiation. Sun also has the most dominating influence on the changing climate of .

Now note the orange rectangle which represents the plane of the equator.

We can clearly see that the two planes do not coincide. That is to say, the Earth is tilted with respect to the plane of the ecliptic. Figure 2 also shows the Earth's axis of rotation. This deviation, or tilt, is called Inclination. We will find that this inclination is vital for seasons on Earth. Make sure to memorize the amont of inclination as we will see this number pop up time and again!

The spinning of the Earth about its axis is called Rotation. One rotation takes about 24 hours or 1 day. Figure 3 reveals two more important parts of the seasons story. This is always the case for the whole Earth, but equal parts of each hemisphere may not be in daylight and darkness.

The dividing line between day and night is called the Circle of Illumination. The orientation of the circle of illumination changes with the seasons.

### Environmental Decision Making, Science, and Technology

Note in Figure 3 that the circle of illumination does not pass through the poles. Look carefully and you will see that more of the Northern Hemisphere is in daylight than in darkness which means that the day is much longer than the night! What is important here is that the changing orientation of the circle of illumination alters the lengths of daylight and nighttime hours.

The second major concept shown in Figure 3 is the Subsolar Point. Figure 3 shows a special event when the subsolar point is as far north as it ever gets, the Tropic of Cancer. The subsolar point is where the sun's rays are most direct and, therefore, most concentrated. The concentration of the solar energy heats the surface.

Important rules emerge from this fact: When the subsolar point is as far north as it can go, it is the Northern Hemisphere's Summer. When the subsolar point is as far south as it can go, it is the Northern Hemisphere's Winter. Figure 4 is a view of the Earth from space showing the circle of illumination.

Earth-Sun Relationship

Again, you can see that half of the planet is all ways in darkness and half is in daylight. The amounts of the northern and southern hemispheres in daylight and darkness, however, may NOT be equal.

Read on and try to answer a question about this diagram posed below. Figure 5 below shows the position of the Earth relative to the sun at four times of the year. You can see that the orbit is elliptical, as described earlier, and that the Earth exhibits a tilt inclination relative to the plane of its orbit around the sun plane of the ecliptic.

Figure 5 also shows how the circle of illumination changes through the year. There is one final element that this figure shows that has a direct affect on seasons. Note the orientation of the Earth's axis. Do you see that the North Pole is always pointing in the same direction in space?

This constant orientation of the Earth's axis in space is called Parallelism. Look at the axis at position A and then at position C.

## Earth-Sun Relationships

Do you see that the axis is parallel in these two positions? Also, note that the axis is again parallel at positions B and D. The inclination of the Earth coupled with parallelism means that at one time of year the North Pole is pointed toward the sun A and six months later it is pointed away C. This shift from A to C and back again causes the circle of illumination and the subsolar point to move and for the planet to experience seasons.

### Earth-Sun Relations and Seasons

When studying the seasons, make sure to note the tilt of the Earth, the position of the subsolar point, the orientiation of the circle of illumination, and the relative lenths of daylight and nighttime hours.

Let's begin talking about seasons at March 21 position D in Figure 5 above and in Figure 6 below. At this point in time, the axis is neither pointed toward nor away from the sun.

This causes the subsolar point to fall on the equator. The circle of illumination also passes through both poles making daylight and nighttime hours equal see below. When daylight and nighttime hours are equal, the event is called an Equinox. The rotation of the earth about its axis also causes the day and night phenomenon.

The length of the day and night depends on the time of the year and the latitude of the location. For places in the northern hemisphere, the shortest solar day occurs around December 21 winter solstice and the longest solar day occurs around June 21 summer solstice. In theory, during the time of the equinox, the length of the day should be equal to the length of the night. The average time the earth takes to move around the sun in approximately days.

This path that the earth takes to revolve around the sun is called the elliptical path. When the sun is moving down from above the celestial equator, crosses it, then moves below it, that point of intersection between the two planes is when the Autumnal Equinox occurs. This usually happens around the 22nd of September. When the Sun moves up from below the celestial equator to above it, the point of intersection between the sun and the celestial equator is when Spring Vernal Equinox occurs.

It usually happens around the 21st of March. During the equinoxes, all parts of the Earth experiences 12 hours of day and night and that is how equinox gets it name as equinox means equal night.

At winter solstice Decthe North Pole is inclined directly away from the sun. At this point it will be at declination This cycle will carry on, creating the seasons that we experience on earth. The earth is tilted At the summer solstice which occurs around 21st of June, the North Pole is pointing towards the sun at an angle of Therefore the apparent declination of the sun is positive At the Winter solstice which occurs around 21st December, the North Pole is pointing away from the sun at an angle of Therefore the apparent declination of the sun is negative