Compare: SC2 & Sky Maps p.4

Both the SC002 and the sky map provide fairly accurate maps of the stars. The SC002 is a polar projection of the northern celestial sphere. One version works for all places on Earth. Sky Maps show the sky at a particular location and time and hence there are as many versions of it as there are times and places. My aim here is to show how these maps relate to each other.

Below find a sky map for CSB/SJU on November 20 at about 8 pm and an SC002. On the sky map the location of the horizon is obvious: it's the red circle that surrounds the stars. Note that I've rotated the sky map to put the northern horizon down: The SC002 shows the northern sky, so we need to adjust the sky map for viewing north. On the SC002 the horizon has no fixed location, but I've drawn it in as it would be on November 20 at about 8 pm: it is the red curve a the bottom with labels for the directions NW, N, and NE. The meridian is the blue line that runs through zenith (labeled with a Z), the north celestial pole (Labeled NCP) and the north point of the horizon.

Lets focus on some constellations in the northern sky. I've marked various constellations on both the SC002 and the sky map. The "Big Dipper" of Ursa Major, circled in green, is near the meridian and quite low in the northern sky. The "Pentagon" of Auriga, circled in orange, is in the NE. The "Northern Cross" of Cygnus, circled in purple, is in the west.

Three hours later the sky has rotated. We must twist the SC002 45° counter-clockwise. Notice that some stars have risen in the NE and others set in the NW. The Big Dipper (green) has shifted to the right, Auriga (orange) is higher in the sky...approaching zenith, and the Northern Cross (purple) is approaching the horizon. The entire celestial sphere is rotating about the NCP.

Three additional hours later the sky has rotated another 45° counter-clockwise. The Northern Cross (purple) is partially below the horizon, Auriga (orange) has just past zenith, and the Big Dipper is now 90° around on its trip around the NCP.