木星上的月影

Jupiter’s volcanically active moon Io casts its shadow on the planet in this dramatic image from NASA’s Juno spacecraft. As with solar eclipses on the Earth, within the dark circle racing across Jupiter’s cloud tops one would witness a full solar eclipse as Io passes in front of the Sun.

Such events occur frequently on Jupiter because it is a large planet with many moons. In addition, unlike most other planets in our solar system, Jupiter’s axis is not highly tilted relative to its orbit, so the Sun never strays far from Jupiter’s equatorial plane (+/- 3 degrees). This means Jupiter’s moons regularly cast their shadows on the planet throughout its year.

Juno’s close proximity to Jupiter provides an exceptional fish-eye view, showing a small fraction near the planet’s equator. The shadow is about 2,200 miles (3,600 kilometers) wide, approximately the same width as Io, but appears much larger relative to Jupiter.

A little larger than Earth’s Moon, Io is perhaps most famous for its many active volcanoes, often caught lofting fountains of ejecta well above its thin atmosphere.

Citizen scientist Kevin M. Gill created this enhanced-color image using data from the spacecraft’s JunoCam imager. The raw image was taken on Sept. 11, 2019 at 8:41 p.m. PDT (11:41 p.m. EDT) as the Juno spacecraft performed its 22nd close flyby of Jupiter. At the time the image was taken, the spacecraft was about 4,885 miles (7,862 kilometers) from the cloud tops at a latitude of 21 degrees.

JunoCam’s raw images are available for the public to peruse and process into image products at: https://missionjuno.swri.edu/junocam/processing.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill (CC-BY)

在这张由NASA朱诺号飞船拍摄的照片中，火山活动频繁的木星卫星伊奥在木星上投下了阴影。就像地球上的日食一样，当木卫一从太阳面前经过时，在木星云层顶部的黑圈内，你会看到一个完整的日食。

这样的事件经常发生在木星上，因为它是一个有许多卫星的大行星。另外，与我们太阳系中的大多数其他行星不同，木星的轴相对于其轨道的倾斜度不是很高，因此太阳永远不会偏离木星的赤道平面（+/- 3度）。这意味着木星的卫星会在全年中定期在木星上投射阴影。

朱诺号与木星的近距离接触提供了一个特殊的鱼眼视图，显示了木星赤道附近的一小部分。这个影子大约有2200英里(3600公里)宽，和木卫一差不多宽，但相对于木星而言显得更大。

木卫一比地球的月亮稍大一点，它最著名的可能是它的许多活火山，在它稀薄的大气层之上经常可以捕捉到喷射喷泉。

公民科学家凯文·吉尔（Kevin M. Gill）使用朱诺号的JunoCam成像仪中的数据创建了这种彩色增强图像。原始图像拍摄于2019年9月11日晚上8:41。 PDT（美国东部时间下午11:41）是朱诺号飞船进行的第22次近距离飞越木星。拍摄图像时，该航天器距离21度纬度的云顶约4885英里（7682公里）。

JunoCam的原始图像可通过以下网址浏览和处理原始图像：https：//missionjuno.swri.edu/junocam/processing。

图片来源：NASA / JPL-Caltech / SwRI / MSSS / Kevin M. Gill（CC-BY）