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PROBL. I.
ON the 12 of May I would find the Suns true place by the former Rules; The Sun enters Gemini May 11; which Substract from 12, the Remainer is 1, which shews the Sun to be in 1 deg. of Gemini the third Sign; that is, 61 degr. from the next Equinoctial-Point.
Let it be required to know the Suns Place the 4th of November; on the 11 day of that Month the Sun enters Sagitarius, and the 13th day of September he enters Libra: betwixt the 13 of September, and the 4 of November is 52 days, and consequently 52 degr. from the Equinoctial-Point Libra; then 30 taken from 52, there remains 22 degr. the Suns place in Scorpio, which is the thing required.
But here is a nearer Rule yet than this, to find the Suns place exactly, and that is by Mr. Vincent Wing's Hypothesis, and Tables in Astronomia Britanica, how to Calculate his true place from Earth, the Rule is,
First, enter the Table of the Middle-Motion of the Sun, and write out the Epocha next going before the time given, under which set the Motion distinctly belonging to the Years, Months, and Days, and Hours, and Minutes, if any be; (only in the Bissextile or Leap-Years,) after February a Day is to be added to the number of Days given; then adding them all together, the sum will be the Middle-Motion of the Sun for the time given.
Suppose the time given be the 12 of May at Noon 1667, at which time the Suns place is required.
Time given. | Longitude ☉ | Apog. ☉ | ||||||
S | D | M | S | S | D | M | S | |
The Epocha 1661 years In∣cluding 6 May. Days 12. | 9 | 20 | 24 | 49 | 3 | 6 | 45 | 5 |
11 | 29 | 33 | 07 | 0 | 0 | 6 | 10 | |
3 | 28 | 16 | 39 | 20 | ||||
0 | 11 | 49 | 40 | 2 | ||||
The Suns Mean-motion, or Longitude. | 2 | 00 | 04 | 15 | 3 | 6 | 51 | 37 |
2. Substract the Apog. of the Sun from his Mean-Longitude, and the Remain will be his Mean Anomaly.
Example. | S | D | M | S |
The Suns Mean-Longitude is | 2 | 00 | 04 | 15 |
The Apogeum Substracted | 3 | 06 | 51 | 37 |
The Suns Anomaly. | 10 | 23 | 12 | 38 |
With the Suns Anomaly enter the Table of his Equation with the Sign on the Head and the deg. descending on the left hand, if the Number thereof be under 6 Signs; but if it be more than 6 Signs, enter with the Sign in the bottom, and the degr. ascending on the right hand, and in the common-Angle you have the Equation answering thereunto; only you must, if need require, remember to take the Proportional part.
S | D | M | S | |
In the Table of Equation answering to 23 degr. is | 0 | 01 | 11 | 51 |
The Suns Mean-Longitude, add | 2 | 00 | 04 | 15 |
The Suns true Longitude. | 2 | 01 | 16 | 06 |
Therefore the true place of the Sun is in 1 degr. 16 min. 6 seconds of Gemini.
In the Year 1583 March 14 at Noon, in the Meridian of Ʋraneburg in Denmark, thrice Noble Ticho-Brahe, most excellently observed the Suns true place in 3 deg. 17 min. 40 seconds of ♈. The time at London was 1583 March 13 day 23 h. 8 m.