# Why does the altitude-azimuth mount have a blind spot near zenith?

I understand the subject mathematically. Azimuth of the celestrial object under track changes a finite 180 degrees instead of a infinitesimal amount as the body passes zenith. This would require infinite rotational speed from the telescope, which is impossible.
But what I need is really a physical and intuitive picture. I just don't understand why the telescope can't simply 'flip over' around the horizontal axis. And how would the telescope actually move to keep track of the object?
I've been searching for a educational illustration or animation, but the best result google offers is this Youtube video

and this picture from Wikipedia. They both illustrate the concept of alt mount nicely, but leave me no clue for the concept of blind spot. I've been staring at them for 20 minutes, trying and failing to mentally picture the process.
Any help would be appreciated, especially if one with an illustration. Thanks!

• Welcome to Astronomy SE! Who says there's a blind spot? I'm not saying there isn't, but it would be better to cite a source, it may help answer authors. Of course some mounts don't have to stop their altitude motion at the zenith and can pass right through it and back down to the other horizon, but that may prove inconvenient for some telescopes. Certainly the big boxy mount with the short stubby telescope in the video can do it, but a long telescope in a short fork can't for example.
– uhoh
Commented Dec 28, 2022 at 10:33
– uhoh
Commented Dec 28, 2022 at 10:36
• Many large observatories use AltAz mounts, like the 8.2m "Very Large Telescope". They make no mention of a blind spot. Amateur Alt-Az telescopes generally do have this blind spot, since they are rarely used for long exposure imaging it doesn't play much role in their function. Commented Dec 28, 2022 at 16:01
• @GregMiller AFAIK the VLT blind spot is within about 0.5 degrees of zenith. Commented Dec 29, 2022 at 0:15