Explanation:
What's that new star in the sky? The star might appear new, but it's actually just the variable star Mira near its brightest. Rolling your cursor over the above vertically compressed image will identify the unusual star Mira, a star that can change from practical invisibility to one of the brighter stars on the sky over the course of a year. Pictured above a castle in Stuttgart, Germany, last week, red giant star Mira appeared near its maximum brightness of magnitude 2. Although similar in mass to our Sun, Mira tenuous and cool atmosphere could extend out past the orbit of Mars, and achieve a luminosity over 10,000 times greater than our Sun. Mira is near the end of its life and its variability is somewhat erratic. Details of Mira's variability are still being researched, but the reason for Mira's pulsations are thought related to periodic changes in the thickness of parts of Mira's atmosphere. Recent high resolution images show that Mira is not even round. Mira lies 420 light years distant toward the constellation of the Monster Whale (Cetus). Mira will fade over the next 200 days, but climb back to naked-eye visibility early next year.
說明:
天空上那顆新的星星是哪顆星呢？這顆星可不是最近才出現的，它是芻蒿增二變星，而現在正是它變得最亮的時候。把你的游標放到上面這幅垂直壓縮過的影像上，就可以找到這顆特別的芻蒿增二，它可以在一年內從肉眼不可見的星星變成天上的亮星之一。上圖，是上禮拜芻蒿增二這顆紅巨星最亮時 (約為2個星等)所拍攝，它就在德國 斯圖加特的城堡上方。雖然芻蒿增二的質量和太陽差不多，但它那相對較冰冷的大氣可延伸到相當於火星軌道般的大小，亮度也是太陽的10,000倍。芻蒿增二是一顆已經接近生命終點的星星，它光度變化的週期也有點不規則。芻蒿增二光度的變化仍是一直被研究的話題，但它的振盪主要是來自於部份大氣厚度上週期性的變化。近年來的高解析度影像顯示出芻蒿增二並不是球形的。芻蒿增二位於鯨魚座 (Cetus)，距離地球約420光年。 芻蒿增二 在接下來的200天裡會慢慢變暗，但在明年年初的亮度又會增至肉眼可見的程度。
影像版權與提供: Stefan Seip (AstroMeeting)
[ 本帖最後由 Sadako 於 2008-5-1 18:05 編輯 ] |
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