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below picture is my probably best attempt, at keylong (can't remember hotel name, something like delykin....??) and shooting while the moon lit the snow peaks.
to share what my friend taught me physically as well as to reiterate all the online readings, first of all, star trails can only be done where there is a lot of visible stars, and secondly relatively free from stray light pollution, usually overseas. avoiding these light pollution partially relies on your ability to frame them away.
to shoot star trail, one has to know where it revolves around. for that, i dunno but i just follow. if u have no one to follow, shoot first then adjust. anyway, the viewfinder is in complete darkness and framing requires multiple tries and adjustment too (while altering the setting). the shooting of cos will require a tripod on steady ground, using a remote control while setting to bulb mode (check your manual, usually is to set exposure to manual and push shutter duration setting over 30s for nikon).
the next step is to set the exposure at the highest ISO and an intermediate aperture of say maybe f/8 to f/11 for a duration of 1min. this gives a test shot of the amount of exposure from the frame. from there, one can decrease the ISO to decrease the exposure or increase the aperture to increase the exposure.
after a suitable amount of exposure is determined. the ISO and aperture can be further adjusted to gives a longer exposure (low ISO and small aperture) while noting that low ISO improves noise control while large aperture gives thicker (and in my opinion nicer) star trails. the maximum duration allowable for some nikon models is 1hr or 30mins with in-camera noise reduction (30mins exposure + 30mins in camera processing).
a few points i have noted, is the frame intensity may keep changing due to the moon (it does moves at night or may be covered by clouds at times) or due to reframing. second point i have noted is having a single stop ND filter might be handy as a two stop ND filter can be a little too tough due to the time limit of the camera.