Earth-Sun Relations and Seasons
The position of the Sun in the sky is a function of both the time and the geographic location of observation on Earth's surface. As Earth orbits the Sun over the course of a year, the Sun appears to move . Thus, the graph of solar declination, as seen from this highly tilted Earth, would resemble a triangle wave rather than a. Part B At the moment shown in the figure of the earth and sun, what is the direction of the gravitational force acting on the earth? The possible directions are. Figure We are showing a vector S' (S-prime) originating at the center of Earth and the meridian that the beam of the sun is intersecting at a given moment.
This correction is less than 0.
The error in calculating the position of the center of the Sun can be less than 0. For comparison, the Sun's width is about 0.
6(h). Earth-Sun Geometry
Atmospheric refraction[ edit ] The declination calculations described above do not include the effects of the refraction of light in the atmosphere, which causes the apparent angle of elevation of the Sun as seen by an observer to be higher than the actual angle of elevation, especially at low Sun elevations. The Sun's declination can be used, along with its right ascensionto calculate its azimuth and also its true elevation, which can then be corrected for refraction to give its apparent position.
Equation of time In addition to the annual north-south oscillation of the Sun's apparent position, corresponding to the variation of its declination described above, there is also a smaller but more complex oscillation in the east-west direction. This is caused by the tilt of the Earth's axis, and also by changes in the speed of its orbital motion around the Sun produced by the elliptical shape of the orbit. Because of rotation, the Earth's surface moves at the equator at a speed of about m per second or slightly over km per hour.
If you could look down at the Earth's North Pole from space you would notice that the direction of rotation is counter-clockwise Figure 6h The opposite is true if the Earth is viewed from the South Pole.
One rotation takes exactly twenty-four hours and is called a mean solar day. At any one moment in time, one half of the Earth is in sunlight, while the other half is in darkness.
2.9 Sun-Earth Relations
The edge dividing the daylight from night is called the circle of illumination. The movement of the Earth about its axis is known as rotation. From the North Pole the rotation appears to move in a counter-clockwise fashion.
- 3. How the Sun shines on the Earth at Different Seasons
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The orbit of the Earth around the Sun is called an Earth revolution. This celestial motion takes 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.
Position of the Sun
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 Change of Seasons Seasons are caused by the Earth axis which is tilted by