Using the Blend Tool, Width Shape Tool and the Gradient Tool you can create this moon with craters and a ring. Fun, quick and easy to create.
Start with a circle, fill it with a color.
Create a smaller circle, fill it with a lighter color. Place it near the top of the first circle.
Create a 3rd circle, make it into an oval and fill it with a lighter color than the other two shapes.
In the Tool Bar, double click on the Blend Tool to open up the dialog box. Choose Smooth Color from the Spacing drop down menu.
Select all the shapes. Using the Blend Tool, click on the bottom of each of the shapes as indicated by the red circles. Start with the top shape, click on the bottom point, then the bottom point of the middle shape, then the bottom shape.
This will create a smooth blend of all the shapes into a highlighted sphere.
Create another circle. Add a stroke and add a gradient fill.
Open the Gradient panel to adjust the colors of the gradient. Click on the gradient color stops to call up the swatches to choose from.
Use the Gradient Tool to change the direction and the distance of the gradient.
Duplicate the shapes (craters) then use the Eyedropper tool to select the attributes of the first circle to make the gradient go the same direction on them all.
For the ring, create an oval, apply an 8 pt stroke.
Use the Width Shape Tool to make one side wider than the other by pulling on the stroke to make it wider.
Select the ring and choose from the Object Menu>Path>Outline Stroke
Using the Group Selection Tool (nested in the Direct Selection Tool), select the outer ring of the moon
Copy the outer ring to put it behind the ring.
Select both the ring and the circle with the Selection Tool. Use the Pathfinder Panel to select the Divide Mode.
After the Divide has been applied, use the Direct Selection Tool to select and delete the shapes you don't need to leave just the ring.
With all the shapes taken away, this leaves the ring with rounded ends that match the shape/arc of the moon.
Move the ring into position. And your moon with craters is done!