How to Approximate the Rising Time 
of a Planet

 

Rising Time of a Planet, How to Approximate the. In the Ephemeris note the sidereal time for the day. If it is for 0h or midnight instead of 12h or noon, add 12 hours. Also note the degree position of the planet. In a Table of Houses for your latitude, find the sidereal time that corresponds to the degree position. The time difference between the S.T. of the planet's position and the S.T. noon position for the day, will be the elapsed time before or after noon that the planet will rise. For example, on Jan. 1, 1940, the Sun was in 9° Capricorn. The S. T. of 6h 38m at 24h Standard Time, becames S.T. at noon, 18h 38m. In Lat. 40°, a 9° Capricorn Ascendant corresponds with S.T. 14h 6m. The difference is 4h 32m before noon, or 7h 28m local civil or mean time - which varies by only a few minutes from the sunrise time given in the almanac. This local mean time should be further corrected to Standard Time by 4m per degree to the nearest Standard meridian. The rising time of any planet can be determined by the same method. v. Table of Houses.

 

The following formula can also be employed:

 

From Ephemeris take:

 

...(1) Sidereal Time on MC at Midnight of desired day.

...(2) Add or subtract 12 = ST at Noon.

...(3) Degree occupied by Sun on the same day.

 

From Table of Houses for desired Latitude, locate in Ascendant column the degree occupied by the Sun, and take from the first column (4) the equivalent ST.

 

Then: (4) - (1) = the arc from Noon to Sunrise, stated in hours;

..................hence the approximate time of Sunrise;

......(2) - (4) = approximate hour of Sunset.

 

Example: For Dec. 17, 1946 at Lat. 40° N

 

...(1) ST at Midnight, 5h 40m + 12 = (2) ST at Noon, 17h 40m

...(3) Long. 24°26'

...(4) Equivalent S.T. 13h 2m

 

.........Sunrise..............Sunset

.......(4) 13h 2m..........(2) 17h 40m

.... - (1) 5h 40m....... - (4) 13h 2m

...........7h 22m AM............4h 38m PM

 

Rice gives 7h 16m AM and 4h 13m PM.

 

To find the approximate time of rising and setting of Venus on that day:

 

From Ephemeris take Venus Long., 20°10'

From Table of Houses take (5) the equivalent S.T....14h 46m

.....Subtract (4) Sun's equivalent S.T..............13h  2m

.....................................................1h 44m

 

Since Capricorn rises after Sagittarius:

 

Venus rises 1h 44m after Sunrise, or 9h 6m AM; and sets 1h 44m after Sunset; or 6h 22m PM.

 

The same process will yield the rising and setting time of any planet.