Write an article based on this summary:

Gather the materials you need to draw the sphere. Trace your circular object on the paper. Choose where your light source will be. Fill the sphere with very light shading. Smooth the shading with a cotton ball or tissue. Add more shading to areas of the sphere that the light source minimally reaches. Repeat smoothing out the shading with a cotton ball or tissue. Darken the outer edges of the sphere, particularly on the bottom and opposite side of the light source. Smooth the darkened shading again. Make the crescent edge opposite the light source the darkest. Rub your cotton ball or tissue over the dark crescent at the bottom to smooth it one last time. Clean up the edges of the sphere by erasing any smudges that escaped the edges.

Article:
This is a basic method for drawing a sphere, so minimal materials are needed.  Sketch pad or paper Pencil Cotton balls or tissues Circular object You can use a small bowl, a glass, a mug, or another object with a circular shape or base. Tracing the circular object allows you to focus on shading the sphere rather than on learning how to draw a perfect circle. Once you decide the angle from which your light source will come, draw an arrow toward the circle from that direction. You will later leave an untouched spot on the sphere, below that arrow, to signify the highlight from the light source. Avoid pressing too hard with your pencil while you shade, as this is your first layer of shading. You will add additional layers of darker shading in later steps. Leave the circular or oval-shaped spot untouched, below where the arrow points from the direction of the light source. Gently rub over the light shading, taking care not to smear the graphite out of the edges of your circle. Remember to leave your highlight spot untouched, so also take care not to smear graphite into that area. Gently shade again around most of the circle, making darker shading on the sides of the sphere where the light source cannot reach. This shading is called the mid-tone. Around the middle of your sphere, you should have about medium tones of shading. Again, take care to avoid smearing the highlight spot and smearing outside the edges of the circle. The light source cannot reach these areas, so naturally, they should be darker. As you get further from the light source, the shading should get darker. However, they should not be as dark at the space directly below the sphere. Maintaining a smooth-looking sphere is important in order to help it look realistic. Use your cotton ball or tissue to do this. This is the final shading step, creating the core shadow. Shade the border moderately dark, and taper it into a crescent shape before tapering off on the other side. Keep this darkest area of shading close to the bottom edge of the sphere; it should be no more than ½ centimeter in thickness. This will help to blend the core shadow into the rest of the sphere. You might also have stray line marks that went outside the edges. Take care not to erase anything within your sphere.