NavList:

While a planetarium might serve as an interesting way to introduce concepts like the celestial sphere, effect of earth rotation and effect earth's orbit on the observed sky; it suffers from a terrific defect.

To wit:  unless the student is precisely at the center of the dome (sphere) of the planetarium screen, severe angular errors are introduced.  The angle measured is directly affected by the baseline or distance. Given four different seats within the planetarium, there will be four different angular readings.  These errors preclude any meaningful reduction of observation.  Indeed, the students will be confused, because they don't get the same answer!  Was it because they absolutely failed at the observation or was it just seat assignment?

If the intent is basic introduction or very basic sextant skills, then there is no real objection.  If however, the student is going to make any steps beyond that very basic introduction, the planetarium suffers.  

Brad