To calculate for example the polaris hour angle I use this formula to calculate polaris hour angle.
τ = θ - α
τ= hour angle
θ= sideral time
α= polaris RA (~ 2h32m)
But where does the α=2h32m come from? Is there a list? Does this change somehow over time? Is my understanding correct that this is the time where polaris crosses the upper meridian at Greenwich?