GEOCENTRIC CALCULATION -------------------- John Pazmino NYSkies Astronomy Inc nyskies@nyskies.org www.nyskies.org 2012 January 8 initial 2013 July 3 current

Introduction ---------- The NYSkies Astronomy Seminar of 6 January 2012 was the first of a two-part set on the Venus and Mars apparition of-2012. Mars was treated on the 6th and Venus will be the topic for the meeting on January 20th. During the Mars discussion the work of Kepler and Copernicus was compared with the Ptolemaeus model of the planets. We saw by sketches on the white blackboard that the geocentric and heliocentric schemes yield the same line of sight to a planet, to the first level of approximation. The main errors in both Copernicus and Ptolemaeus are their use of only uniform circular motions which can not properly duplicate the real elliptical motion of the planets. The errors are greatest for the more excentric orbits of Mars and Mercury but are tempered for the more circular orbits of Venus, Jupiter, Saturn. I here go thru one calculation with the geocentric model for Venus and Jupiter. By good chance Venus has both an almost circular orbit and appearance in the night sky now. Mars, while in the night sky now, has too elliptical an orbit for good results.

The exercise ---------- Besides Jupiter also having an almost circular orbit like Venus, there happens to be on 2012 March 14 a mutual conjunction of Jupiter and Venus. The two planets stand on the same ecliptic longitude, with Venus a few degrees north of Jupiter in latitude. Since we ignore latitude here, we allow the two planets to coincide on that date. Conjunctions were one way that early astronomers cross-checked their work. They calculated such conjunctions and looked if in fact the two planets lined up in the sky. If one or the other computation was wrong, because of math or procedure error, the planets would not be in the proper places and the conjunction occurs early or late. With the simplified uniform circular model here there will be a discrepancy of a couple degrees in our computation here. In spite of this, the exercise brings out some curious and important features of planet motion.

Geocentric model -------------- In the simplified scheme of pure circular paths and pure uniform circular motion a planet moves in a small circle, the epicycle, that in turn moves around the Earth in a larger circle, the deferent. There is no real body at the center of the epicycle, just an empty point. Since to the ancient astronomers the planets had no material substance like mass or bulk, there was no problem with them moving in the opicycle with no apparent cause. This factor also maintained the premise that real motion may be only around Earth as a real center. The speed of the epicycle around Earth is the mean angular speed of the planet and its position along the deferent is the mean longitude of the planet. Ptolemaeus and his school knew nothing of orbits as such but did understand that there were two periods associated with each planet. One was the sidereal period which we know as the planet's own year. The other is the synodic period, the time to complete one round of the epicycle relative to the Earth. It is also the period for a complete apparition of the planet relative to the Sun in the sky. The interplay between these two period, when judiciously adjusted, does described closely the planets as they course thru the stars. Such was the strength of the Ptolemaeus system. In the era of naked eye observations and crude mathematical tools, the system did work.

Epicycle ------ The Prolemaeus system treated each planet independently of the others. There was no 'system' of 'unified organism' of planets. He notes in his book 'Almagestum' that there is no way to know the distances to the planets to place their deferents in rank above the Earth. He used a traditional order of the planets based on angular speed thru the zodiac. The Moon moved fastest to earn the lowest deferent. Next up were Mercury, Venus, Sun, Mars, Jupiter. Saturn, the angularly slowest, occupied the highest deferent. Since distance were not factored into the Ptolemaeus model, the deferent of each planet was set to unity radius for each planet. This amounts to superimposing all the deferents into one with the many epicycles coursing along it. Ptolemaeus did not suggest this. Future authors maintained ranked deferents to prevent collisions among the planets as they sweeped along in their epicycles. The epicycle is sized relative to unity to make the planet move as it does in the sky. In adjusting the epicycle size Ptolemaeus ended up making the epicycle and deferent ratio equal to the ratio of size for the planet's and Earth's orbit around the Sun. This was beyond him and his school to appreciate until Copernicus inverted the epicycle into an orbit around the Sun. Note carefully that for an inferior planet the epicycle maps to the planet's heliocentric orbit and the deferent maps to Earth's orbit. The epicycle radius is (planet orbit radius) as a fraction of the Earth orbit radius. For a superior planet the epicycle maps to Earth's orbit while the deferent maps to the planet's orbit. The epicycle radius is 1/(planet orbit radius). In both cases the deferent has a radius of unity. We have for the two planets ---------------------------------------------------- parameter | Venus | Jupiter | Sun ----------------+-------------+-----------------+---- synodic period | 583.9 day | 398.9 day | --- symodic arc | 575.51 deg | 393.17 deg | --- sidereal period | 224.6 day | 4332.6 day | 365.25 day deferent radius | 1.000 | 1.000 | 1.000 epicycle radius | 0.723 | 1/5.202 = 0.192 | --- prev apogee | 2011-08-16 | 2011-04-06 | 2011-03-20 ------------------------------------------------------------ The 'apogee' for the Sun is his vernal equinox. We do not use the real apogee of the Sun in his excentric deferent. These are the fundamental parameters describing the planets. As we progress thru the exercise we compute others based on these. The values are from modern solar system parameters. Note well that the SUn has no proper synodic period or epicycle. The parameters are discussed in detail further in this piece.

Mercury and Venus --------------- These two planets posed major problems for the early astronomers. While the Moon, Sun, Mars, Jupiter, Saturn nitida mente fell into rank above Earth, Mercury and Venus showed no obvious proper place. Authors placed both below the Sun, both above, one above and one below. No author that I know of suggested that Mercury or Venus were so close to the Sun that its epicycle overlapped the Sun's deferent. There could be times when the planet was under the Sun, closer to Earth, and others when over the Sun, farther from Earth. The usual scheme has Mercury, then Venus, then Sun. in order above Earth. This is the order employed for naming the days of the week, making it impossible now to promote a revised order

Superior conjunction ------------------ The concept of superior, and inferior, conjunction implies that the planet actually passes above or below the Sun. We are so used to these terms that we may forget that in the pure Ptolemaeus system the ranking of planet deferents was indeterminate. The more historicly correct statement is that Venus comes to apogee, farthest from Earth, regardless of where the Sun is. The inferior conjunction is the perigee, again with no regard to the real location of the Sun. That Venus reaches apogee when she is lined up with the Sun is treated as good luck, there being nothing in the model of either Sun or Venus to require the two line up at Venus's apogee. They just do. In the usually adapted order of planets, the interval between deferents allows that their epicycles do not interfere. Venus never ascends higher then the Sun. At the highest farthest point on her epicycle Venus is still lower than the Sun. Both of her conjunctions, at the apogee and perigee of the epicycle, are inferior to the Sun. By great fortune we can keep the terms inferior and superior conjunction for the same aspect of the planets relative to the Sun! When Venus is at superior conjunction she is in fact beyond the Sun in her orbit. For inferior conjunction she is under the Sun. In 2012 she actually crosses his face.

Elongation -------- The angular distance in the sky of a planet from the Sun is the elongation of the planet. It is measured downrange along the ecliptic, being (planet's longitude) minus (Sun's). Due regard for crossing 360 deg/0 deg is taken at the vernal equinox. By this sense of the difference, elongations east of the Sun are positive to appeal to the planet's presence in the evening sky for convenient viewing. West elongations, with the planet in the morning sky, are negative. Elongation may be stipulated around the full 360 degrees entirely as a positive value or as east (positive) and west (negative) value up to 180 degrees. The latter is the more common practice altho it requires rectifying the longitude difference into this range. Whole revolutions around the ecliptic are generally discarded to leave the elongation within 360 degrees. Ecliptic latitude is ignored for elongation. The planet's actual angular separation from the Sun is the diagonal of the planet's latitude and elongation. It is very nearly just the elongation except when the planet is angularly very close to the Sun. Aspects of the planet relative to the Sun are certain standard elongations. Of interest in this piece are the conjunctions, when the elongation is zero. Note well that the planet may be up to several degrees of latitude north or south of the Sun. In this exercise it happens that Venus at her inferior conjunction with the Sun in 2012 is exacta mente on top of (under, in front of) the Sun in a transit with almost zero latitude.

Calendar maths ------------ We need a way to do calendar maths. Some calculettes, mainly those for finance and business, have calendar functions. Sci/tech models generally lack them. Here is a method of maths that is quick simple and accurate consistently to within one day over many centuries. Write the two dates as 'year-month-day'. We do this step by step for the interval from Venus's apogee to the Venus-Jupiter conjunction

2012 03 14 Ven-Jup conj -(2011 08 16) previous apogee

Subtract EACH FIELD SEPARATELY! Do NOT borrow or carry! This is an algebraic operation with the signum specificly written. I put the subtrahend date in parens to remind that the minus applies to all of its fields and not just to the year.

2012 03 14 Ven-Jup conj -(2011 08 16) prior apogee ---- --- --- +1 -05 -02

Do NOT miss out the signa! Leave one out or mistakenly assume it will cause no end of grief later in your calculations. We now convert all fields into days. Each year is 365.25 day, This is the Julian year, close enough to the tropical or sidereal year of Earth. Each month is 30.44 day, 1/12 of the year. Each day is itself. Hours within a day are (hour)/24 decimal of a day. Add together the converted parts of the difference between dates, minding very well the signum of each:

+01 year = +365.25 day -05 month = -152.20 day -02 day = -02.00 day -------------------- +211.05 day

Venus moved from her prior apogee to conjunction with Jupiter in 211.05 days. This method is surprisingly good for just about all home astronomy purposes, being consistently within one day of the precise result. Do not use this maths for critical work, like occultations. For such applications you have to go thru a more accurate computation or avail of a fin/biz calculette. An other way is to convert all calendar dates to Julian Day Numbers and convert the result to calendar date.

Synodic period ------------ The planet moves in the zodiac at a speed different from the Sun's. It must at some moment line up with the Sun and be lost from view in daylight or strong twilight. After a few weeks the planet emerges into weaker twilight to begin an apparition. It stays in view, moving thru the zodiac until eventually it is lost from view again at the opposite twilight. A few weeks later it passes the Sun again. The interval between Sun passes, conjunctions, is the synodic period. It is also the length of each apparition or complete round of elongations from the Sun, the apogee on the epicycle. There is an other sense of synodic period is often lost in modern home astronomy. If Mars is 40 degrees east of the Sun now, he'll again stand 40 degrees east of the Sun one synodic period later. He was there one synodic period earlier. It is well to say that the synodic period is the interval between recurrences of the same place in the planet's epicycle. The conjunction of the planet with the Sun in traditional astronomy is not visible in the sky. It occurs against the Sun in daylight. In modern times we can observe the planet at conjunction in pictures captured of the Sun by the SOHO satellite. It orbits the Sun at the Sun-Earth L1 Lagrange point, well beyond the daylight caused by our atmosphere. Its LASCO-3 camera cover a 7-degree radius around the Sun to image the outer corona. The pictures show background stars that float by the Sun in successive pictures. By examining pictures taken within a few days of conjunction the planet slides past the Sun. An outer planet like Jupiter has only one conjunction with the Sun per apparition. It is, in the Copernicus model, on the far side of the Sun in superior conjunction. 'Superior' is commonly omitted because there is only this one lineup with the Sun. Venus and Mercury, inferior planets, have two conjunctions with the Sun. Some authors say there are two apparitions, one between each pair of conjunctions. The more usual treatment is to consider the full cycle of Venus as one apparition with two conjunctions and two intervals of viewing.

Synodic arc --------- While the planet is cycling around its epicycle, the epicycle is carried around the Earth on the deferent. After one synodic revolution in the epicycle, the planet has displaced a fixed distance downrange in the zodiac. Staying with the start of the cycle at apogee, superior conjunction, the epicycle center is lined up with the planet, so the displacement between apogees is also that for the very planet in the zodiac. Wanderings of the planet, the retrograde loops and stations, cancel out along the way. By counting the motion from apogee we also place the Sun against the planet. The angular length of the synodic arc is the distance run by the Sun during one synodic period of the planet. The synodic period times the daily motion of the Sun yields this angular displacement. We state the length of the arc as the distance run by the Sun in the zodiac between apogees. This is NOT necessarily the amount the epicycle, carried by the deferent, moved! Jupiter and Saturn do not whiz around the zodiac in a year and then a few more degrees. Jupiter's synodic period is about 393 days and its synodic arc is the distance the Sun runs in those days, or about 388 degrees. The very planet move only those extra 28 degrees, over the one lap of 360 degrees. This leads to the rule that Jupiter spends one year per zodiac sign as he orbits the Sun.

Sun's arc ------- The Sun's model has no epicycle and no synodic period. To track the movement of the Sun we bank him off of the vernal equinox. When the Sun stands at this point in the ecliptic his longitude is zero degrees. For spans of a few decades we can neglect the effects of precession. Precession causes a westward drift of the vernal equinox along the ecliptic of quite one degree in 72 years. The motion of the Sun is smooth enough to fully describe with a slightly excentric deferent. There is an apogee in early July and a perigee in early January. The Sun advances in the ecliptic a bit faster or slower but for our purposes here we assume a uniform speed thruout the year. This speed is the full 360 degrees circuit of the zodiac divided by the 365.25 days it takes to complete it, or (360 deg)/(365.25 day) = 0.9856 deg/day. For casual calculations, we commonly use 1 deg/day, like for assessing the position of constellations for a given date.

Sidereal period ------------- A second period associated with the planet is the sidereal period. This is not recta mente observable but was well known to the ancient astronomers. They needed both periods to manipulate their model of planet motion. They knew utterly nothing about orbits as such. The sidereal period was found by watching the planet go thru its synodic cycle and applying the formula

(planet sid cyc) = (Earth sid cyc) - (planet syn cyc)

In this formula we count CYCLES, ROUNDS, LAPS and NOT periods, spans,intervals. This is important!! We also count the laps of an inferior planet as a NEGATIVE number and a superior planet as a POSITIVE number. For the two planets we have from almanacs covering 2008 thru 2012 the following superior conjunctions --------------------- Venus | Jupiter ------------+-------- 2008 Jun 9 | 2009 Jan 24 2010 Jan 11 | 2010 Feb 28 2011 Aug 16 | 2011 Apr 6 2013 Mar 18 | 2012 Nay 13 ------------------------- For Venus we have 3 synodic cycles completed in 1743.93 days or 4.7746 Earth sidereal cycles. Recall that we define the year by the rounds of Earth in her orbit or of Sun in his deferent. Jupiter goes thru 3 synodic cycles in 1205.51 days or 3.3032 Earth laps. Then we get --------------------------------- item | Venus | Jupiter --------------+----------+-------- Earth sid cyc | 4.7746 | 3.3032 plan syn cyc | -3 | +3 diff cycles | 7.7746 | 0.3032 Earth/diff | 0.6141 | 10.8946 plan sid per | 224.31 | 3979.25 day ------------------------------------- Venus sidereal period is close to the true value but Jupiter is too short. The maths are correct but the premise of uniform circular motion is off. In the 2008-2012 span Jupiter happens to be near his perihelion and moves faster in his orbit. This faster motion carried thruout the orbit by the calculation makes for a quicker completion of the lap. The lesson here is that we don't need hundreds or thousands of years of record as some authors assert. Observations for only a few decades or a century are enough. This span smooths out the irregularities of the planet motion, like the faster pace near Jupiter's perihelion, to yield surprisingly accurate sidereal period. This method was in history the one employed by babylonian astronomers, who compiled the first good tables of planet motions.

General procedure --------------- We obtain the location of the planet and its elongation from Sun as follows. First, for each planet, count the days from its previous apogee to the conjunction. This gives us the fraction of both the synodic period and synodic arc for that planet. We then count the days from the previous vernal equinox to the conjunction and also from the previous apogee. We need both intervals. The latter places the Sun at the planet, he being in conjunction with the planet. This is the longitude of the planet from which it steps forward to the Jupiter-Venus conjunction. The former gives the longitude of the Sun at conjunction, by which we obtain the elongation of the planetary encounter in the sky. We finally get the deviation of the planet from the epicycle center. This is generated by the planet's movement in the epicycle and may be east or west of the epicycle center. This is the 'wandering' portion of the otherwise smooth direct movement of the planet. The longitude of the planet is the longitude of the Sun at the last apogee, plus the fractional synodic arc to conjunction, plus the deviation around the epicycle. The elongation of the planets, both in conjunction, is their longitude minus that of the Sun. If all goes well we should find the planets have almost equal longitudes and are situated in the early evening sky.

Sun's longitude ------------- We find the ecliptic longitude of the Sun by counting forward from the previous vernal equinox, when the longitude was zero degrees. The prior equinox before 14 March 2012 is 2011 March 20. We can also bank off of the next equinox of 2012 March 20 by backing off the Sun's longitude. We do both to cross-check our work. ------------------------------------- item | prev V E | next V E -------------+-------------+--------- Ven-Jup conj | 2012 Mar 14 | 2012 Mar 14 vern equinox | 2011 Mar 20 | 2012 Mar 20 elapsed days | +359.25 day | -6 days Sun's long | +354.09 deg | -5.91 deg tossed laps | +354.09 deg | +354.09 deg ---------------------------------------------------

Apogee longitude -------------- When the planet is at the apogee, at the farthest highest point in the epicycle, it is also in conjunction with the Sun. The longitude of the apogee at this moment is the longitude of the Sun. It is found by pacing the Sun from the vernal equinox to the apogee. We could have banked off of the 2012 vernal equinox and probably should do so as a double-check on our work. I did this, not shown here, and all looks copasetic. ------------------------------------ item | Venus | Jupiter ------------+--------------+-------- apogee date | 2011 Aug 16 | 2011 Apr 6 prev ver eq | 2011 Mar 20 | 2011 Mar 20 raw elapsed | 0 +5 -4 | 0 +1 -14 elapsed per | 148.20 day | 16.44 day elapsed arc | 146.07 deg | 16.20 deg apogee long | 146.07 deg | 16.20 deg -------------------------------------- Do understand well that is is the movement of the epicycle center, NOT of the very planet, from its previous apogee to the vernal equinox. Because the vernal equinox is zero degrees, this movement puts the apogee at its longitude.

Mean longitude ------------ Mean longitude is the fraction of the synodic arc from the previous apogee plus the longitude of that apogee. We got the apogee longitude above because this is also the Sun's longitude on that date. ----------------------------------- item | Venus | Jupiter ------------+-------------+-------- Ven-Jup con | 2012 Mar 14 | 2012 Mar 14 prev apogee | 2011 Aug 16 | 2011 Apr 6 raw elapsed | +1 -5 -2 | +1 -1 +8 elapsed per | 211.05 day | 342.81 day synodic per | 583.9 day | 398.9 day symodic arc | 575.51 deg | 393.17 deg elapsed arc | 208.18 deg | 367.45 apogee long | 146.07 deg | 16.20 deg mean long | 354.25 deg | 383.65 deg tossed laps | 354.25 deg | 23.65 deg ------------------------------------- The apparent discrepancy between the longitude of Venus and Jupiter, hardly a conjunction situation, comes from the fact that both planets are off of their apogees, in an other pars of their epicycles. We must compute a correction based on the fractional revolution of the planet in the epicycle and this is the hard part of this exercise. You NEED trigonometry and a sci/tech calculette.

The hard step ----------- There is no real body at these mean longitudes, only the mathematical point at the center of the wpicylcles. The final step, which is the toughest, is to find the deviation of the planet, the angle from the epicycle center as seen from Earth. This involves some trigonometry to solve various triangles. At this point you BETTER make a sketch of the planets, which I have here for Venus. Due to ASCII limitations I leave out the actual circles of deferent and epicycle.

+A +J

+X

+V

+E +O

A is the apogee of the Venus epicycle. V is Venus somewhere more or less near her location on the epicycle. X is the center of the epicycle on the Venus deferent. E is Earth. We look from the north on to he planetary system. The epicycle is the circle around X, its center, passing thru A and V. The deferent is the circle around E passing thru X. The angle from the vernal equinox O around Earth E to X is the mean longitude of Venus. Angle AXV is the synodic angle of Venus, the portion of the full 360 degree of the epicycle run by Venus since apogee. Angle XEV is the displacement of Venus throwing her off of the mean longitude location of line EX. We got so far the mean longitudes of Jupiter and Venus and now must find the displacements from those positions..

Synodic angle ----------- The angular movement of the planet around its epicycle is counted from the apogee and is in classical works called the anomaly. This angle is not an observable one, there being no such thing as an epicycle but is an intermediate quantity that goes into other calcs to yield the place and motion of the planet in the sky. By convention, to keep the algebraic signa consistent, the synodic angle for an inferior planet is counted anticlockwise as a positive value and clockwise as a negative one for a superior planet. You can remember this by the direction the planet emerges from superior conjunction with the Sun. When Venus leaves apogee she heads into east elongation from the Sun, making her displacement a positive angle. Jupiter leaves his apogee into west, negative, elongation. The angle is found by the portion of the synodic period elapsed since the previous apogee. This same portion was applied to the synodic arc to get the mean longitude since the apogee. The synodic angle for Venus and Jupiter are ------------------------------------- item | Venus | Jupiter --------------+-------------+-------- Ven-Jup conj | 2012 Mar 14 | 2012 Mar 14 prev apogee | 2011 Aug 16 | 2011 Apr 6 elapsed per | 211.05 day | 342.81 day synodic per | 583.9 day | 398.9 day synodic ratio | 0.3614 | 0.8594 synodic angle | 130.12 deg | -309.38 deg ---------------------------------------

Next step ------- Here's where your work can go horribly wrong without a diagram and clear understanding of how angles behave. The synodic angle AXV is the portion of 360 degrees traveled by the planets. ---------------------------------------------------------- item | Venus | Jupiter | in Venus diagram -------------+------------+-------------+----------------- deferent rad | 1.000 | 1.000 | line EX epicycle rad | 0.723 | 0.192 | line XA synodic ang | 130.12 deg | -309.38 deg | angle AXV interior ang | 49.88 deg | 129.38 deg | triangle EXV planet dist | 0.769 | 1.132 | line EV, Cosine Law deviation | 46.00 deg | 16.33 deg | angle XEV, Sine Law ------------------------------------------------------------- I used the Law of Cosines and Law of Sines, wxplained below, to get the missing parts of triangle EXV, for Venus and a similar triangle for Jupiter.

Planet longitude -------------- We're almost done. The longitude of the planet is the mean longitude plus the deviation. Do watch for any rollover thru 360 degrees. -------------------------------- item | Venus | Jupiter -----------+------------+-------- mean long | 354.25 deg | 23.65 deg deviation | 46.00 deg | 16.33 deg true long | 400.25 deg | 39.98 deg tossed lap | 40.25 deg | 39.98 deg sign | 10 Taurus | 9 Taurus ---------------------------------- The last line is merely the sign-angle notation, truncated to the degree, for the ecliptic longitude. The ecliptic is divided into 12 signs of 30 degrees each. The 30-degree blocks of longitude are named after the 12 zodiacal signs. In astronomy and most astrology the degrees within a sign are numbered 0-29. Some astrologers use 1-30.

Observability ----------- Where are the planets relative to the Sun and to the sky? This is shown by the elongation of the planets from the Sun, their longitude minus that of the Sun. Because we found the longitudes are the same, the planets being in mutual conjunction, we need only one calculation. --------------------- item | planets -----------+-------- true long | 40 deg, rounded Sun's long | 355 deg, rounded elongation | -315 deg tossed lap | +45 deg --------------------- The planets are about 45 degrees east of the Sun, placing them in the evening sky in twilight. They set in early night. Note that Venus is near her eastern greatest elongation, where she sat on March 27th.

Sines and cosines --------------- I used the law of Sines and law of Cosines to get the deviation of the planet from the center of the epicycle. Because in astronomy these two trig tricks are so handy, yet so little known among home astronomers, I explain them here. First, I must remind that these are valid ONLY for plane, flat, triangles, NOT triangles on a sphere. You can not use these directly on the sky, for example. There are spherical versions of the laws which I sip here. The Law od Sines is the simpler of the two. In the triangle here the capital letters are the angles and small letters are the sides. Each side is opposite an angle of the same letter. The triangle is NOT a right triangle but we'll see what happens when it is.

A----------c---------------B \ / \ / b a \ / \ / C

sin(A) / a = sin(B) / b = sin(C) / c

This is easy! Yet if we know all three sides we can get all three angles. You do need that sci/tech calculette to get the angle itself that has the function value you found. The Law of Cosines is a bit more fiddly and demands close attention to the singa of each item.

c ^ 2 = a ^ 2 + b ^ 2 - (2 * a * b * cos(C))

A common mistake is to miss taking the square root of c^2 after doing the rest of the maths. Your result is all wrong, specially if side c goes into a downstream calculation. For both formulae do not ever assume the signum of an item! Write it in and apply it in the maths. What's with the right triangle? Angle C is 90 degrees. Cosine of 90 degrees is zero. The whole term with cos(C) zeros out. We got

c ^ 2 = a ^ 2 + b ^ 2

which is our good friend the Pythagoras Law! For the Law of Sines with anfgle C as the right angle, we note that c is the hyptonuse and sine(90) = 1. Then

sin(A) / a = sin(B) / b = 1 / c

For each term of this equation

sin(A) = a / c

sin(B) = b / c

which are the very definition of the sine function in a right triangle.

Conclusion -------- On 14 March 2012 both planets are really in longitude 40 degrees, 10 Taurus by modern computation methods. We ignored latitude effects. making the two planets essentially coincident on the ecliptic. They are really about 3 degree north of Jupiter. The procedure here is definitely a first-order approximation and is intended to illustrate the way planet positions are calculated in the geocentric model of the solar system.