851 meters per hour is about 0.0000000008 times as fast as The Speed of Light.

The speed of light (and all other electromagnetic radiation) in a perfect vacuum is known as "c" and measures exactly 1,079,252,850,000 meters per hour, per the formal definition of the meter. While visible light travels close to this speed in air, it slows to 719,501,899,000 meters per hour when passing through the glass of a typical window.

In other words, it's 0.0000000007885084580 times the speed of The Speed of Light, and the speed of The Speed of Light is 1,268,217,210 times that amount.

(C) (in a vacuum)The speed of light (and all other electromagnetic radiation) in a perfect vacuum is known as "c" and measures exactly 1,079,252,850,000 meters per hour, per the formal definition of the meter. While visible light travels close to this speed in air, it slows to 719,501,899,000 meters per hour when passing through the glass of a typical window.