180204期:金星与三个紫外波段下的太阳

金星与三个紫外波段下的太阳

在2012年发生了一次不同寻常的日食。通常,日食现象的产生是因为月亮运动到了太阳与地球之间,但在2012年,金星扮演了月亮的角色。如同月亮造成的日食样,随着金星与太阳逐渐重合,金星的相位逐渐变成更加纤细的娥眉状。最终,二者完美重合,金星相位降为零,成为一个太阳表面的暗斑。从技术上来说,这可以称得上是金星造成的日环食,只不过其外围好似巨大无比的火环。上面这幅摄于掩食阶段的影像里,太阳是由其动态观测卫星所拍摄的三个紫外波段的影像叠合而成的,右侧的暗区是日冕洞。数小时后,随着金星在轨道上持续行进,纤细的相位复现。要见到下一次的金星凌日,得等到2117年。

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Venus and the Triply Ultraviolet Sun
Image Credit: NASA/SDO & the AIA, EVE, and HMI teams; Digital Composition: Peter L. Dove

Explanation: An unusual type of solar eclipse occurred in 2012. Usually it is theEarth’s Moon that eclipses the Sun. That year, most unusually, the planet Venus took a turn. Like a solar eclipse by the Moon, the phase of Venus became a continually thinner crescent as Venus became increasingly better aligned with the Sun. Eventually the alignment became perfect and the phase of Venus dropped to zero. The dark spot of Venus crossed our parent star. The situation could technically be labeled a Venusian annular eclipse with an extraordinarily large ring of fire. Pictured here during the occultation, the Sun was imaged in three colors of ultraviolet light by the Earth-orbiting Solar Dynamics Observatory, with the dark region toward the right corresponding to a coronal hole. Hours later, as Venus continued in its orbit, a slight crescent phase appeared again. The next Venusian transit across the Sun will occur in 2117.

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