Astronomy Picture of the Day

Explanation: This sequence of false color X-ray images captures a rare event - the passage or transit of planet Mercury in front of the Sun. Mercury's small disk is silhouetted against the bright background of X-rays from the hot Solar Corona. It appears just to the right of center in the top frame and moves further right as the sequence progresses toward the bottom. The dark notch is a coronal hole near the Solar South Pole, while a flaring coronal bright point can be seen to the left of the notch in the top frames. The frames were recorded on November 6, 1993 by the Soft X-ray Telescope on board the orbiting Yohkoh satellite. Transits of Mercury (and Venus) were historically used to discover the geometry of the solar system and to map planet Earth itself.

這組假色X射線影像，記錄了一個罕見的事件 - 水星通過太陽前方的行星凌日。 影像裡，水星小盤面的剪影以背景熾熱日冕的明亮X射線輻射為襯托。 事件啟始時，水星位在最上方圖板的中右方，隨著時間推移滑向下方的圖板並向右移動。 影像裡的暗色凹口是太陽南極附近的日冕洞，而在最上方圖板的凹口左側，可以看到一個突然亮起的日冕亮點。 這些影片定格是在1993年11月6日，由陽光號（Yohkoh）衛星上的軟X射線望遠鏡所記錄。 水星（和金星）凌日在歷史上，常被用來找出太陽系的幾何形狀及繪製地圖。