EXPLANATION OF PLANET DIAGRAM

Evening Post, Volume CXXIII, Issue 1, 2 January 1937, Page 22

EXPLANATION OF PLANET DIAGRAM

The planet diagram enables the approximate times of rising and setting of the sun and principal planets to be found for any night during the year 1937. The diagram is constructed for latitude 40 degrees South, but should be useful for approximate times in any part of New Zealand. As an example ot its use, suppose it is required to find what planets will be visible in the svening sky on August 18, 1937. Running up the vertical line, marked August 18, the time of sunset is seen to be about 17h 30m (5.30 p.m.). The next :urve to cut the August 18 line indi:ates that Mercury sets about 19h 10m (7.40 p.m.). Mercury would therefore be visible in the west for about two hours after sunset.' Proceeding up the August 18 line, Saturn rises at about 20h 35m (8.35 p.m.); so that from that time onwards Saturn would be risible somewhere in the eastern sky. Tha diagram also indicates that Mars

sets just before 2h the following morning, and must therefore have been : visible during the previous evening. ■ Next, Venus rises at 4h 40m, and 1 Jupiter sets at sh. Thus Jupiter would , have been visible the previous evening, but not Venus. Finally, sunrise : occurs at about 6h 50m. Having found whai; planets will be visible on the evening of August 18, it is possible to ascertain from the diagram approxi- . matetly in what part of the sky to look for them at any particular time. For instance, at 21h (9 p.m.) on August 18 Mercury will have set and will be no longar visible. Saturn has just risen (at 20h 35min—8.35 p.m.) and will therefore be visible low down to the east. Since Mars sets at about 2h and Jupiter at 5h on the following morning, both these planets will be well away from the western sky at 21h (9 pin.), and Jupiter would be to the east of Mars.