在本研究中，我們嘗試計算得出落日時的天文折射現象。在光線通過大氣層的過程中，它會因為受到大氣層折射的影響而使光線的路徑逐漸彎曲，這即為天文折射現象。天文折射現象的彎曲程度受到天體的仰角所影響，在天頂時最小而在地平面時最大。天文折射現象是受到空氣的密度所影響，其與空氣的溫度和壓力息息相關，為了得到大氣的垂直密度結構，我們使用中央氣象局的雷文送（無線電探空儀）傳回的大氣垂直資料。我們用來比對的落日照片是在2011年9月17日，2011年10月17日與2011年10月28日在淡水海邊所拍攝。將拍攝的落日與建模計算的落日仰角進行比對，兩者間的差異最小時是在天體仰角高度為0.749674°時，差異量為-0.70"；兩者間差異量最大時是在天體仰角高度為1.387341°時，差異量為123.72"。

關鍵字：天文折射、落日、折射、大氣層、雷文送、觀測

In this work, we try to calculate the astronomical refraction of the setting sun. The light path from a source outside the earth’s atmosphere is a curve due to the astronomical refraction, and this curve depends on the observed location and the angle between celestial body and the horizon, especially when the celestial body is near the horizon. The astronomical refraction is influenced by the density and temperature of the vertical atmosphere structure. The CWB rawinsonde observed data is used to construct the vertical density structure of the atmosphere. The sunset images taken on the September 17, 2011, October 17, 2011 and October 28, 2011 at Tamshui, and thes images are used as comparison of model and observed astronomical refraction of the setting sun. The difference of the model and the observed setting sun in minimum is -0.70" when the un-refracted incident angle is at 0.749674º above the real horizon, in maximum is 123.72" when the un-refracted incident angle is at 1.387341º above the real horizon.

Key Words: Astronomical Refraction, Sunset, Refraction, Atmosphere, Rawinsonde, Observe

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