A telescope that is mounted on a vertical axis or moves only a small amount from the vertical. It is primarily used to determine positional measurement of stars moving near the zenith. The advantage i
s that there is no atmospheric refraction occurring at the zenith. If a star on one night passes through the center of eyepiece, one must observe it six month later, and see if the star has been offset by the center. A shift would mean a measure of parallax.
The persistence of a nearly constant temperature, very close to the freezing point, during annual freezing (and occasionally during thawing) of the active layer.
The persistence of a nearly constant temperature, very close to the Freezing Point, during annual freezing (and occasionally during thawing) of the Active Layer. The Zero Curtain results from the diss
ipation of the Latent Heat of fusion of water during freezing or thawing of the ground. It can persist for several hours or several weeks depending largely on the total water content of the ground, Snow Cover and air temperatures.
The persistence of a nearly constant temperature, very close to the freezing point, during annual freezing (and occasionally during thawing) of the active layer