* Altitude: The altitude of a star setting due west is 0 degrees. Altitude is the angular height of an object above the horizon. When an object is setting, it's touching the horizon.

* Azimuth: The azimuth of a star setting due west is 270 degrees. Azimuth is the angular measurement of a celestial object from north, going clockwise around the horizon. Due west is precisely 270 degrees from north.

Important Note: This assumes we're talking about a perfect "due west" setting. In reality, the star might be slightly north or south of due west, causing its azimuth to be slightly different from 270 degrees.