Question:
Where was Victor Ambartsumian educated in May, 1928?

Context:
 Victor Ambartsumian attended Herzen University from Jan, 1924 to Jan, 1925. 
 Victor Ambartsumian attended Pulkovo Observatory from Jan, 1928 to Jan, 1931. 
 Victor Ambartsumian attended Faculty of Physics and Mathematics of the Saint Petersburg University from Jan, 1925 to Jan, 1928.

Answer:
Pulkovo Observatory