For latitude 60°N, the celestial equator extends from due east on the horizon to due west on the horizon, crossing the meridian at an altitude of 90°- 60° = 30° (in the south). Because the start with the dec = +30° lies 30° to the north of the celestial equator on the celestial sphere, it must cross the meridian at a point 30° to the north of where the celestial equator crosses, which means at an altitude of 60°. The same reasoning explains the rest of the rankings, for example, the star with dec = -20° lies 20° to the south of the celestial equator on the celestial sphere, so it must cross the meridian at a point 20° to the south of where the celestial equator crosses, which means it’s at an altitude of 10°.
Therefore, the answers are as follows:
Nearest the Horizon
dec = -20 degrees
dec = -5 degrees
dec = +0 degrees
dec = +10 degrees
dec = +30 degrees
Farthest Above the Horizon
