DSST Astronomy

# The is an independent unit probably invented by man

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The _________ is an independent unit probably invented by man, although its length may have been based on the interval between the quarter phases of the moon. Week. The seven days of the week are named for the seven planets including the sun and moon as recognized by the ancients. Basic Properties of Light and an Intro to our Solar System A speed of 186,282.397 miles per second is called the speed of ___________. Explanation: Light. The speed of light is the highest possible speed and universality of the observed speed is one of the postulates of the theory of relativity. The fact that the speed of light is finite means that the deeper into space we look, the further back in _______ we are seeing. Time. Looking far into space is actually looking back in time. That's because the light that is reaching our telescope left its origin a long time ago. For instance, if we're looking at a galaxy 10 billion light years away, that light took 10 billion years to reach us--we're looking back in time 10 billion years! The ____________ to a surface is simply a line or direction perpendicular to that surface at that point. tion: Normal. This term is used when discussing the laws of optics and visible light. The law of ______________ describes the manner in which light is reflected from a smooth, shiny surface. Explanation: Reflection. If light strikes a shiny surface, it must make a certain angle (the angle of incidence) with the normal to the surface at the point where it strikes. The angle it forms with the normal to the surface as it reflects is the angle of reflection.

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The law of reflection states that the angle of reflection is equal to the angle of incidence, and that the reflected ray lies in the plane formed by the normal and the incident ray (in other words, all three line up): The law of ______________ deals with the deflection of light when it passes from one kind of transparent medium into another. Detailed Explanation: Refraction. Every transparent substance can be characterized by its index of refraction, a measure of the degree to which the speed of light is diminished in passing through it. Whenever light passes from a medium having one index of refraction into a medium having another index, it is always bent or refracted at the interface between the two media. The image below illustrates the refraction of light as it passes from air through glass and then back to air. _____________ of light is the manner in which white light, which is a mixture of all wavelengths of visible light, can be decomposed into its constituent wavelengths or colors when it passes from one medium into another. The beam of light is spread out or dispersed. Explanation: Dispersion. The phenomenon of dispersion occurs because the index of refraction of a transparent medium varies slightly for light of different wavelengths. Whenever light is refracted in passing from one medium into another, the violet and blue light of shorter wavelengths is always bent more than the orange and red light of longer wavelengths. Nature provides an excellent example of the dispersion of light in the production of a rainbow.
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