Steering by the stars at night is one of a sailors oldest tricks. You pick an easily identified star more or less directly in front of the boat and head for it. You align it with a stay, shroud, or other convenient reference point and then by careful steering keep them aligned. It is a great way to steer and you will soon notice that even the smallest deviation from your coarse is noted by your stars movement much faster than by the compass. When you really must “steer small” at night this is the way to do it. But that old trick is also fraught with traps for the unwary.
First, the star you choose should not be too high in the sky, no more than about 45 degrees. The higher the star, the harder it is to notice deviations from your coarse. To understand this imagine how a star right over your head would appear not to move at all no matter what coarse you steered; where as one just above the horizon would respond to the slightest change in heading. So, lying on your back looking up at the stars while steering is completely out me hardies.
Next, your intended heading has a lot to do with how accurate your star will be for steering. If you are going East or West then all you need consider is how long before your star sets or gets too high to be useful. But, if your are heading North or South – and not using the pole star or Southern Cross- the stars appear to move from East to West as the night progresses which means that over 4 hours you can see up to 60 degrees of shift. I think there are still 15 degrees to an hour. One can never be sure in this fast passed age of electronics. In any case the drift can be up to 5 degrees every 20 -30 minutes. More than enough to put the skipper in a passion after a 4-hour watch. How you compensate is up to you. Some pick a star on an East or West heading, something more or less off the beam and use that. Takes a bit of practice but it works just fine. Others are more exact and demand a new star every time the coarse shifts by 5-10 degrees. Myself, being a typical lazy sailor, I just shift my bottom a bit to compensate for the stars movement as I see the coarse drifting on the compass. Bring the boat on the proper heading and then scoot your butt over a bit until your star seems to move back to where you wanted it to be. Saves a lot of headache and gives me a good excuse to move around a bit.