This graph represents the direction and power of thermal emission from Pioneer 10 at a distance of 25 AU from the Sun. The spacecraft's antenna points toward the top of the graph; the direction of spacecraft motion is toward the bottom of the graph. If Pioneer 10 radiated heat away in all directions equally, the plot would look like a circle (dark blue line). But Pioneer 10 does not radiate heat isotropically; the thermal model predicts that most of the power comes out the sides of the spacecraft, with almost none radiating directly along the spacecraft's direction of motion (magenta line).

NASA / JPL / Slava Turyshev