What does this number measure?
The Messier catalogue hosted by LAMOST relates an angular diameter of 20 arcminutes and a distance of 25 100 ly to an extent of about 145 ly. The visible size varies with the depth of the observation.
Compare the stated dimensions
The comparison uses the number in each fact sheet: altitude, height, diameter, length or distance, depending on the reference. Two values in metres do not necessarily describe the same property.
Source and limitations
Rounded documentary extent. Boundaries are diffuse and depend on the observations and convention used; this is not a distance from Earth.
Original schematic illustration, not a photograph. Shapes, colours and details are interpreted; only the stated dimension is compared.