Today's word is . . . heliosphere!
Heliosphere uses the same Greek root as the word "helium," which is "helios," meaning the Sun. Sphere of course, implies something spherical. Together, the heliosphere, is basically a sphere of helium.
Along with all the light it's putting out, the sun fires out a constant spray of charged particles in every direction. Any object in its vicinity is constantly experiencing pressure from the sun as this wash of particles pushes against it. Astronomers call that "the solar wind," because it pushes out from the sun like a wind.
Now, if you could look at the sun from very far away, you would see that the solar wind has produced a humongous bubble of gas around the sun. It's a bit like blowing a soap-bubble, where your breath is the solar wind. However, the bubble around the Sun is huge; its edge is four times as wide as Neptune's orbit.
That bubble of gas is in a spherical shape, creating the heliosphere!