The US Naval Observatory Astronomical Applications Department has a website that calculates rise, set, and transit times for the Sun, Moon, planets and bright stars for the period 1800 to 2050. The link to this site is https://aa.usno.navy.mil/data/mrst

The site gives the following preamble: “The output table also includes azimuth at rise and set, as well as altitude at transit. The altitude and azimuth values are for the center of the apparent disk of the object. The altitude values include the effect of atmospheric refraction when the object is above the horizon . The azimuth values are computed with respect to true north (not magnetic). The user can specify the height of the observer, which can range from the surface of the Earth to a maximum of 10,999 m (the top of the troposphere). It is assumed that the observer’s horizon is flat (i.e., no geometric ‘dip’ is applied) and unobstructed. This data service incorporates a model that determines the angular refraction by numerically integrating a ray passing through a simple polytropic atmosphere.”

“Rise and set times are tabulated to a precision of one minute only (i.e., no seconds are tabulated). This is because the observed times of rise and set are affected by random changes in local atmospheric conditions and other local variables which cannot be accurately modeled.” This last comment is interesting for those who believe that astrology was based on observation. It is essentially saying that determining the precise actual time of sunrise or sunset is beyond the scope of our astrological software because random changes in the local atmospheric conditions and other local variables cannot be accurately taken into account by the programs that we use. In other words, there is a kind of “uncertainty principle” regarding timing based on any astrological technique that requires an accurate time of sunrise or sunset at a particular location.

To show the usefulness of this site for astrologers, let’s look at an example. This chart belongs to a man who has recently experienced his Saturn return. It is cast in the tropical zodiac with Placidus houses, geocentric coordinates and true lunar nodes. It is a diurnal chart with the Sun above the horizon. The native was born on a Jupiter day during a Mercury hour, the 5th hour of the day as can be seen by the location of the Sun in the half of the 10th house closer to the 11th cusp where the 4th hour of the day ends.

If Claudius Ptolemy were reading this native’s chart, he would have begun his analysis by estimating the native’s longevity. First, he would determine the “life-giving” planet, which in this case is the Sun. It is a diurnal chart and the Sun is powerful in the angular 10th house which forms a whole-sign sextile to the Capricorn Ascendant.

Next, Ptolemy would identify the planet most inimical to life in this chart. Here, the most harmful planet would be Mars, the “lesser malefic” which belongs to the nocturnal sect and is particularly unfortunate in a diurnal chart. Mars is also peregrine (without essential dignity), conjunct the 12th cusp (undoing) and conjunct Jupiter (the ruler of the 12th in the 12th). In addition, the “greater malefic” Saturn, which is also peregrine (without essential dignity), has recently stationed Rx, and is mutually applying to square Mars.

Both Mars and Jupiter are disposited by Jupiter, which rules and occupies the 12th house; and both are in square aspect to the planet Saturn. In fact, with the Moon in partile opposition to Mars, this chart features a powerful T-square of the Moon on the cusp of the 6th house (illness) opposing Mars and Jupiter on the cusp of the 12th house and square to Saturn Rx in Pisces in the 2nd house. According to Morinus, planets in the 2nd house “accidentally” signify the matters of the opposite 8th house (mortal dangers). Here, Saturn in 18 Pisces in the 2nd casts its opposition into 18 Virgo in the 8th, which is ruled by Mercury and occupies the term of 12th ruler Jupiter.

Ptolemy would next ask when the life-giving Sun would meet with life-negating Mars via primary motion (the turning of the sky from east to west after birth). In other words, Mars at birth lies near the cusp of the 12th house, so Ptolemy would want to know when Mars as it rises from the Asc to the MC will be at a position in its daily motion equivalent to where the Sun is in this chart, that is, in the 10th house several degrees away from the cusp of the 11th.

This is where the US Naval Observatory site comes in handy. If we enter the date and location of the native’s birth, we can calculate the following data for the Sun and Mars:

For Mars:

[Note: Initially, I made some slight errors reading the above. I have corrected these in this update of the text. The results are essentially the same. Given that the times involved are correct only to the nearest minute on the clock, the final result of a date for the perfection of a primary direction will have an “orb” of a few months and cannot be expected to be exact.]

Given this data, Ptolemy would compute how far along their daily semi-arcs were the Sun and Mars when this native was born at 10:43 AM (apparently timed to the nearest minute on the clock).

The Sun rose at 6:42 AM (accurate to the nearest minute on the clock) and birth occurred at 10:43 AM, a difference of 241 minures on the clock, out of a total of 312 minutes in the Sun’s semi-arc: 241 / 312 = 0.7724, or 77.24% of the Sun’s travel from the Asc to the MC.

Mars rose at 9:02 AM and birth occurred at 10:43 AM, a difference of 101 minures on the clock, out of a total of 285 minutes in Mars’ semi-arc: 101 / 285 = 0.3543 or 35.43% of the Mars’ travel from the Asc to the MC.

When will Mars be 77% of its way between the Asc and the MC on its diurnal semi-arc, which will place Mars in an equivalent position to where the Sun is at birth with respect to both the horizon and the meridian?

77% of the 285 minutes in the semi-arc of Mars equals 220.13 minutes after Mars-rise, which we must add to the time of Mars-rise so that Mars will arrive at an equivalent position with the natal Sun. BUT Mars had already moved 101 minutes from Mars-rise when the native was born, so 220.13 minutes minus 101 minutes = 119.13 minutes after birth.

Ptolemy converted this number of minutes to the native’s age by the simple formula one degree of timing on the Equator in RA equals one year of life. Here, Mars will be proportionately at the same position as the natal Sun when 119.13 minutes have passed after birth. Dividing 119.13 by 4 clock-minutes per year gives the result of 29.78 years old, or around 29 years 9.4 months of age.

Naibod used a different “key” for timing in which the average daily motion of the Sun equals on year of life. At the Naibold rate, natal Mars will align with the Sun at age 30.297 years, or around 30 years 3.6 months of age (around the end of January of 2026).

I find that the midpoint of the age indicated by the keys of Ptolemy and Naibod is often a good estimate of the timing of an event. In this case, 29.78 + 30.297 = 60.077, which gives an average (midpoint) of 30.04 years, or age 30 years and 14 days. Since this native was born on 9 November 1995, the primary direction of the Sun to Mars, measured by Ptolemy’s method of proportional semi-arc and timed by the midpoint of the Ptolemy and Naibod keys, would be expected to manifest about half a month after his birthday on 9 November 2025, that is, arround 23 November 2025. In reality, this young man died unexpectedly on Sunday 19 October 2025, within about a month of the predicted date. Because the recorded time of birth is specified only to the nearest minute on the clock, and the time of sunrise is also calculated to the nearest minute on the clock, these calculations may be off by up to two minutes, which implies an accuracy to within about 6 months (each clock-minute corresponding to about 3 months in timing).

Calculting this native’s directions by proportional seim-arc around ages 29-30 in Janus software, using the recorded birth time of 10:43 AM, we get the following results, shown with both Ptolemy’s and Naibod’s Key:

In the list of directions without latitude, Mars is carried to the position of the natal Sun on 26 Sep 2025 (Ptolemy Key) or on 4 March 2026 (Naibod Key), the midpoint of these dates being mid-December of 2025. This list was compiled using only the conjunction and the traditional aspects (sextile, square, trine, opposition), and it is apparent that 2025 is likely to be a highly stressful year, especially the period between September of 2025 when Mars aligns with the Sun by primary motion, according to Ptolemy, and March of 2026, when Mars aligns with the Sun by primary motion, according to Naibod. When the Sun was directed to the conjunction or hard aspect of Mars, medieval astrologers considered it a critical period, potentially indicating illness, danger, or even the risk of death, depending on other factors in the chart.

If we calculated the direction of the Sun to Mars with latitude (here Mars is below the ecliptic and has a latitude of 00 S 49′), then this direction with latitude, using Ptolemy’s Key, would perfect on 23 October 2025, which is very close to the event of 19 October 2025. With the Naibod key, it would perfect 01 April 2026.

Next is the Polar Chart of this native from NOVA Chartwheels, giving a view of the natal planets spread out around the Earth’s Equator from a point in outer space directly above the North Pole of the Earth’s axis. Wwe want to know how long it will take Mars (the anaereta) to move to the fixed position of the Sun (hyleg) as the sky appears to rotate from east to west after birth:

Another way to look at this chart is through the ancient method of “circumambulation.” With the Sun as the “life-giver,” we would let primary motion carry the zodiac across the natal position of the Sun. Doing so, we would see that around age 29 – 30 years, the position of the harmful planet Mars in Sagittarius in the term (bound) of Venus, which also contains the 12th cusp (sorrow, misfortune, undoing), aligns with the Sun.

At the time of the unexpected passing of this man, his distributor (divisor) was Venus, which ruled the Venus bound of Sagittarius containing the natal 12th cusp, Mars, and the opposition aspect of the Moon — part of the powerful T-square linking Mars, Moon, Saturn, Jupiter and the significations of the 6th, 8th and 12th houses.

If we consider his Profections, at age 29 he is in a 6th sign from the Asc profection year with a Gemini Asc, ruled by Mercury. Gemini being the profected Ascendant activates the Moon on the 6th cusp in Gemini, with the Moon squaring Saturn and opposing Venus, Mars, Jupiter and the 12th house cusp — a very stressful T-square in the birth chart..

With Mercury as the hour lord at birth, the Lord of the Orb or Turn at age 29 becomes the Moon, which also activates the stressful T-square in his chart.