Star movement rates near pole

Date: April 23rd
Time: 10:00 PM

Brief

   Yesterday I showed the location of the north celestial pole (n-c-p) with the celestial grid.  By doing so, it indicated one key thing: if stars were placed north of any of the gridlines that cleared the horizon, they would be circumpolar.  That part is obvious when looking at the lines.  What may not be as noticeable, is that the more circumpolar stars seen at a particular latitude, the less a viewer sees of the opposite hemisphere.  As shown a few dates back with constellations such as Scorpious, with the entire constellation clearing the southern horizon at transit, it makes me feel fortunate to beable to do most of my viewing from a mid-northern latitude, when close to home.

Detailed

   For today, I am still looking directly north, yet this time with the altitude/azimuth (alt/az) grid instead of the celestial one.  The altitude grid verifies how high we would be viewing when looking directly at the n-c-p. 

It is also a reminder of how far a star is from cardinal north (azimuth 0º) when it is before or after transit.  The closer a star is to the north axis, as the celestial grid showed in past entries, the less of a variance there is for that star in both azimuth and altitude.  When a star transits, that is when azimuth rate changes the fastest at most latitudes.  When very close to the n-c-p however, and about to transit, the altitude changes at its slowest.  The opposite holds true for both when the star is furthest from transit, changing rate extremes: azimuth changes the least when the star is the same altitude as the n-c-p, which is just under 6 hours before and after transit.
   To further show the following, I will include a second image of the both the alt/az and the celestial grids overlapping with a 2º field.  By doing so, and remembering that the stars follow the celestial gridlines, it can help understand the change of altitude and azimuth rates.  Polaris is the star that we will use for example, for both, being close enough to the n-c-p.

*click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.