A telescope for exact definition of celestial bodies. In the beginning of the 19th century instruments like this attained high level of perfection and became obligatory part of the numerous large observatories.
Well-known centre of their production was the work-shop of T. L. Ertel, where in 1828 the meridian circle for the first state Russian astronomical observatory was produced.
It is oriented according to the line of St.-Petersburg meridian in the eastern pavilion of the observatory on marble pillars, which originated from dissembled St. Isaac's Cathedral. To work with it a special astronomical slot opening was arranged.
The diameter of the objective is 120 mm, focal distance — 1600 mm, weight is about 100 kg.
At the late 1940-ies the Ertel's meridian circle was transferred from the Pulkovo Observatory to M. V. Lomonosov's Museum of the Academy of Sciences and re-installed in its historical place.
In 2004 — 2005 it was restored, some details were reconstructed.