A balloon floated across the sky.

气球飘过天空。

《新英汉大辞典》

Finally, the balloons are beautifully placed across the sky, but the red balloon in the upper left of the frame is the final, key element to the success of the image.

最后，气球美丽地横跨在天空里，然而画面左上角的红色气球是成功拍摄这张照片决定性的关键元素。

youdao

Like a conventional mirror, a solar balloon of this sort must be turned to face the sun as it moves through the sky, and Cool Earth is testing various ways of doing this.

这样一颗太阳能气球，就像传统的太阳能反射镜板一样，必须随太阳横越天空时移转面向，所以酷地球公司正在进行各种使气球转向的实验。

youdao

After a delay of almost four weeks the BBC Sky Balloon finally got off the ground in County Fermanagh.

BBC: Giant weather balloon carries out its sky mission

Where it would land, no one knew but, using a GPS tracker, the BBC Sky Balloon team tracked the payload to the Killynick Road, Derrylin, near the border with the Irish Republic.

BBC: Giant weather balloon carries out its sky mission

Conflicting reports emerged about the company that operated the doomed balloon, Sky Cruise.

CNN: Deadliest balloon crash in decades kills 19 in Egypt