How do I make a hollow sphere? So my journey here is only days old, but am already struggling. I am trying to duplicate this:

I've watched countless videos and repeated the best I can learn so far. So on my first sphere I've created this:

At a different angle:

As you can see, I've created the hole, but the cylinder I used is now sticking out the other side, which I'm not sure how to remove, any thoughts?
Is this really the best way to create those hollow spheres, similar to the planets picture I pasted?
I downloaded blender yesterday (V. 2.83.1). Many of the YouTube videos I've watched are difficult to follow and often only relate to older versions, so finding one that will be 2.8 specific has proved to be difficult (might be that I'm so new to Blender so finding it difficult)
It looks as if you already used a cube with subdivision surface modifier to get your sphere. While not a bad idea, i'd recommend to use at least subdivision level 4 for a cleaner sphere, otherwise it's not really as spherical as you'd want.
Thanks to Trey Harper for pointing out the cast modifier, i barely use, which in this case though really improves the result.
That said, going from your (cube)sphere:

Apply the subdivision surface modifier on your cube(remember lvl 4, for a more spherical sphere) and a cast modifier with the factor of 1:

Marked red, important before going on is to apply these modifiers in order!
Go in front view Num 1, activate edit mode Tab
and x-ray mode Alt+Z, select half of the sphere like this:

when selecting, leave the center deselected to keep a half
With the selection, press X and choose Vertices
In the Object Data Properties we need to activate the Normals&gt;Auto Smooth:

Auto Smooth is needed for the next step to look clean at the cut
Go back in object mode Tab and add a solidify modifier.

Adjust the modifier to your needs and you have one shell done.

You can now copy Shift+D the created shell and adjust it's size to gain the other layers of the planet.
Here a little visual demonstration:

The thickness of each layer can easily be adjusted in the modifier
As the core looks like a full sphere, you should have all needed means to your cause now.
Happy Blending