1. Stars do not really twinkle, they just appear to twinkle when seen from the surface of Earth. The stars twinkle in the night sky because of the effects of our atmosphere. When starlight enters our atmosphere it is affected by winds in the atmosphere and by areas with different temperatures and densities. This causes the light from the star to twinkle when seen from the ground. 2. Dispersion of light is the key concept to answer this question. Sunlight consists of photons of different wavelengths, which are refracted at different angles at the front surface of raindrops. The violet light (the lowest wavelength seen by eye) is deviated the most from the direction of incidence, the red light (the greatest wavelength) is deviated the least. The light is then reflected at the drop's back surface and refracted one more time at the front surface, when leaving the drop. As a result, the angle between the directions of incidence of the white light and the direction of returning of the violet light is 40o. The same angle is 42o for the red light. The red light from a raindrop, high in the sky, can reach the observer because it is deviated the most from the direction of incidence. This drop is seen as red. The violet light from the same drop passes over the observer, because it is deviated the least. In order to be seen as violet, a raindrop should be located lower in the sky. Thus, a rainbow is red on top and violet on the bottom. the third question is incomplete

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