Rashi: They have backs ¹ . Malbim - these are the fixed stars ² that stand over them. They are numerous to count and too distant to measure. They stand on Galgalim and wheels of Kochvei Leket (the sun, moon and five closest planets).

Rashi #1: They scare one who sees them ¹ .

Rashi #2: They stand in fear [of Hashem].

Radak: Anything extraordinary in quantity is called Pele and Nora, like "El Am Nora", "me'Eretz Nora'ah" (Yeshayah 18:2, 21:1), or exceptional in quality, like "ha'Kerach ha'Nora" (below, 22).

Malbim: The stars and their wheels are tall beyond measure, and all the more so the fixed stars in the milky way (our galaxy). Modern physics explains that their orbits are due to gravity, which pulls small stars towards big stars. It is as if they fear to distance from them, and is drawn to it. Chazal said that they fear Devar Hashem, who decreed that they be drawn to the center of their orbits.

Rashi: Their eyebrows ¹ .

Radak: This is the masculine form of v'Gabeihen. The verse changed [gender] due to the repetition ² .

Malbim: Their Gav (back) is full of innumerous fixed stars and suns that illuminate to afar without limit in every direction. Since each star influences what is below it, and via it Hashem oversees everything, they are Hashem's open eyes that constantly conduct the entire existence.

Rashi: They can see in all four directions, for they do not turn when they go.

Malbim: Refer to 1:18:3:3.