火星上的日行跡
Martian Analemma <br />
<br />
<img src="http://i19.tinypic.com/2lx7ct3.jpg" border="0" onclick="zoom(this)" onload="attachimg(this, 'load')" alt="" /><br />
<br />
數位圖示版權和提供: Dennis Mammana (Skyscapes)<br />
<br />
<font color="navy">Explanation:</font><br />
<font color="darkred">On planet Earth, an analemma is the figure-8 loop you get when you mark the position of the Sun at the same time each day throughout the year. But similarly marking the position of the Sun in the Martian sky would produce the simpler, stretched pear shape in this digital illustration, based on the Mars Pathfinder project's famous Presidential Panorama view from the surface. The simulation shows the late afternoon Sun that would have been seen from the Sagan Memorial Station once every 30 Martian days (sols) beginning on Pathfinder's Sol 24 (July 29, 1997). Slightly less bright, the simulated Sun is only about two thirds the size as seen from Earth, while the Martian dust, responsible for the reddish sky of Mars, also scatters some blue light around the solar disk.</font> <br />
<br />
<font color="navy">說明:</font><br />
<font color="darkred">在地球上，如果每天同一時間在同一地點記錄太陽的位置，一年過後，就會得到一個8字型的日行跡 (analemma)。如果在火星上進行類似的工作，所得到的圖案會簡單一些，會是個被拉長的梨形。這張以火星探路者號著名火星全景圖為背景的示意圖，呈現了火星日行跡的形狀。這張模擬圖假設是從薩根記念站 (Sagan Memorial Station)觀看傍晚的太陽，每隔30個火星日記錄一次 (首次在地球曆1997年7月29日)。從模擬可知火星的太陽沒地球亮，太陽的大小只有地球的三分之二，火星的塵埃讓天空變得紅紅的，也會散射來自日盤的藍光。</font><br />
<br />
<font size="2">資料來源: Scientific American<br />
Department of Physics, NCKU</font>