Introduction to Spherical Astronomy: p. 13

Term: SC002 star map

The SC001 provides a map of the equatorial region of the celestial sphere. We also need a map near the north celestial pole. The Mercator-type projections are increasingly inaccurate as we move away from the celestial equator, so a different type of projection is needed. Polar projections map the poles so that a pole is at the center, and the hour circles (which all meet at the poles) radiate out as straight lines, and the diurnal circles which surround the pole, are displayed as circles. For a north polar projection, declination=90° is at the center, the inner-most circle has declination=80°, followed by 70°... The outer-most circle on the SC002 has declination=30°, so there is a lot of overlap between the outer edge of the SC002 and the top of the SC001. RA is measured around the circles, with 0^h at the top, 6^h on the right, 12^h on the bottom, and 18^h at the left. You should be able to roll up your SC001 into a cylinder and place your SC002 on top and have the RAs match up. Remember the star side should be found on the inside of the cylinder!

The below diagram shows how we could make a polar projection of the south celestial pole. It's the same process for the north celestial pole.