Mercury (planet) at a steep angle. Mercury is 10° above the horizon when the planet appears directly above the Sun (i.e. its orbit appears vertical) and is at maximum elongation from the Sun (28°) and also when the Sun is 18° below the horizon, so the sky is just completely dark. This angle is the maximum altitude at which Mercury is visible in a completely dark sky. At middle latitudes, Mercury is more often and easily visible from the Southern Hemisphere than from the Northern. This is because Mercury's maximum western elongation occurs only during early autumn in the Southern Hemisphere, whereas
The Secret of the Ninth Planet Plutonians dead, the danger to the solar system is past. Burl sees then the people of other planets and of other stars coming together in peace and mutual understanding. The book was reviewed by “When the power of the sun becomes noticeably diminished, young Burl Denning and his expedition take off in an anti-gravitational ship to discover the cause and its location. After a dizzying tour of all the planets, they realize that the trouble springs from Pluto, a belligerent planet which is trying to usurp the life-giving power which the sun gives earth. Making an alliance with the friendly