I resorted to using “scope rows and cols” instead of “id” and “header”. Is this a big deal? I feel for time sake, using “scope” is efficient but perhaps using “id” and “header” could be more meaningful for the impaired.
I think it’s a much easier way to use scope. The outcome is probably the same for assistive technologies. Both concepts connect the <td>s to their corresponding <th>s
Here are some small points to consider:
The slash at the end of a self-closing tag like <meta> isn’t needed anymore.
When using <colgroup> all columns need to be listed. There should be a third entry: <col span="9">.
All the *span and scope attributes are correct except for “Dwarf planets*”. Since it’s a single row it should be scope="row".