Lecture_5_1-22_

Lecture_5_1-22_ - Angular measure See box E-1 in text...

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Angular measure • See box E-1 in text • Around a whole circle = 360 o = 360 degrees •( The Earth moves about 1 o per day around the Sun.) •1 o is divided into 60 arc minutes = 60’ • 1’ is divides into 60 arc seconds = 60” • Do not confuse arc minutes and seconds with minutes and seconds of time
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Some angles in the sky.
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An object appears at a larger angle when it is closer Angular size in radians = size/distance See box E-2 for details Since we can measure the angle with a telescope, if we know the size of an object, we can find its distance, and vice-versa. We won’t do any calculations with this, but you need to know the concept, and the units of angular measure.
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Fig E.20 in text Fig 10.1 in text Using parallax to measure distances to astronomical objects
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Using Parallax • The radius of the Earth’s orbit is defined as 1 astronomical unit = 1 AU = 93,000,000 miles • Using the baseline of the diameter of the Earth’s orbit = 2 AU, measure the parallax angle to get the distance to the star
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Parsecs as distance • Parallax angles are small – all less than 1 arc second • The distance for which the parallax would be 1” is called a “parsec”. • Parsec is a common astronomical unit of distance equal to about 3.3 light-years.
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Reflection and Refraction Law of reflection Angle of incidence = angle of reflection Law of refraction n 1 sin ± 1 = n 2 sin ± 2 N = index of refraction
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Both a positive lens (thicker in the middle) and a concave mirror can converge parallel light to an approximate focus. (The simple lens has color errors in its focus, and it takes
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Lecture_5_1-22_ - Angular measure See box E-1 in text...

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