Whats the spinning thing inside the telescope mount?
The “wrong” time on the clock shows the sidereal time, which is which “line of celestial longitude” (the technical term is “meridian of right ascension”) is passing overhead. We define a “day” to be the time it takes the Sun to complete one circuit around the sky. Since the Earth is constantly moving in its orbit around the Sun, this period is longer than the time taken for Earth to spin once around its axis by around 4 minutes. As a result, a particular meridian of right ascension is overhead 4 minutes earlier each successive day, so sidereal time gains 4 minutes a day relative to clock time. (This is why the constellations change with the seasons: over time we’re looking out at different sections of the sky.) At the start of an evening’s observing we use the sidereal time to calibrate where the telescope is pointing. There is a “right ascension calibration wheel” on the telescope column, consisting of two disks with graded tick marks—vaguely reminiscent of a sundial, except it’s flat
