The Total Solar Eclipse Model
The Total Solar Eclipse (TSE) is the greatest and the grandest event in the solar system. There is probably no other event in the solar system that is so beautiful as a TSE and this model tries to give the observer an idea of how a real solar eclipse would look like.
The model shows a filter sun (the sun as seen through a solar filter). The filter sun is to be viewed from a long distance of about 20 meters. The moon starts covering the sun from one side -- the first contact. The moon moves further and when it covers more than 99% area of sun's disk, a glorious diamond appears at one of the edge of the sun. As the moon moves further the intensity of diamond decreases and the corona begins to appear around the sun. This gives the diamond ring effect. The diamond fades away as the moon covers the sun completely -- the second contact. The intensity of the corona continues to grow due to the increasing adaptation of the eye to the darkness. This stage of totality remains for about a minute or two. As the totally nears an end, a streak of light appears on the other side of the sun -- the third contact. This light increases in intensity to form the second diamond while the background corona appears to shrink and the combination gives rise to the second diamond ring. The eclipse ends when the last edge of moon leaves the sun's disk -- the fourth contact.
Technical Details
The TSE model is a computer controlled model showing how a real solar eclipse would look. It is basically a light effect. The intensity of various bulbs is controlled using Pulse Width Modulation. Each bulb is controlled using a single pin from the parallel port. There is no DAC anywhere in the driver circuit. The duty cycle of the square wave from each pin is varied according to predefined law. There is a driver circuit outside the paralled port. It has driver transistors and power transistors working in switching mode. The circuit amplifies current to 3 Amps required for the bulbs to operate when.
Model at work
Following are two images images of the the model at work. The first one is a partial phase showing about 75% sun eclipsed. The second one shows the corona and a the almost faded diamond. Both the photos are overexposed.
| Fig 1. | 75% eclipsed sun |
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| Fig 2. | Totality |
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Below are two images of the model with the controlling computer and emergency control panel. This is in case anything goes wrong with the computer or the parallel port. Thus the model can also be controlled manually in case the computer is not available
| Fig 3. | The model with the PC and emergency control panel |
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| Fig 4. | This image shows me sitting besides the model. Notice the driver circuit connected to the parallel port. of the PC |
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Here are some snaps of the model taken with a Black & White CCD camera connected to the TV Tuner card of my PC. These images incredibly seem to be of a real eclipse but are infact the different stages in the model demonstration.
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