月光三重奏

The Moon (left), Saturn, and Jupiter (lower right; Saturn is above and to the left of Jupiter) were seen in the sky above the Washington Memorial on Dec. 17, 2020. At the time, Saturn and Jupiter were nearing each other in the sky, culminating in a “great conjunction” on Dec. 21, where they appeared a tenth of a degree apart.

Great conjunctions between Jupiter and Saturn happen every 20 years, making the planets appear to be close to one another. This closeness occurs because Jupiter orbits the Sun every 12 years, while Saturn’s orbit takes 30 years, causing Jupiter to catch up to Saturn every couple of decades as viewed from Earth.

The last great conjunction was even more special: Jupiter and Saturn had not appeared that close in the sky to each other since 1623.

For skywatching tips, visit What’s Up.

Image Credit: NASA/Bill Ingalls

2020年12月17日，在华盛顿纪念馆上方的天空中看到了月亮（左）、土星和木星（右下；土星在木星的左上方）。当时，土星和木星在天空中彼此靠近，最终在12月21日出现“大近合”，相距十分之一度。

木星和土星之间的大近合每20年发生一次，使这两颗行星看起来彼此很近。之所以如此接近，是因为木星每12年绕太阳一圈，而土星每30年绕太阳一圈，从地球上看，木星每几十年就会赶上土星。

上一次大近合更加特别：自1623年以来，木星和土星从未在天空中如此接近。

有关观星小贴士，请访问观星指南。

影像来源: NASA/Bill Ingalls