(reflector telescope with primary mirror formed of spinning liquid)
A liquid mirror telescope is a reflector telescope
whose primary mirror is formed of a rotating
open container of a reflective liquid such as mercury,
i.e., a liquid mirror.
Under gravity, the upper surface forms into
an upward-facing concave parabola,
useful for a reflector telescope.
However, the resulting mirror is in a fixed position,
aimed straight up, though very slight aiming can be
accomplished by moving the rest of the optics,
with some decrease in the quality of the image.
The the International Liquid Mirror Telescope (ILMT) is an example liquid mirror telescope
and the Large Zenith Telescope (LZT) is a past example.