When do planets point in the same direction as the sun and when do they oppose the sun?
Look at "conjunction, conflict, wide distance, and stay" separately, and then calculate the respective moments.
Planets and Small Solar System Objects
Some planets are suitable to be found after sunset, while others come to the opposite direction when the sun sets. The original book estimated these sky configurations using mean event times plus period corrections. It doesn't just add a fixed period to the calendar.
Guess first
When a planet "stays", does it really stay in space?
Show answer and explanation
No, it’s the change in the direction seen by the earth that temporarily stops. — This is the apparent motion relative to the earth and cannot be regarded as the actual revolution of the planet.
Then connect experience and science
First define the phenomenon while standing on the earth
Conjunction means that the planet and the sun are in the same longitude direction, and opposition means that they are half a circle apart; the inner planets also have superior conjunction and inferior conjunction.
First distinguish the definition of phenomenon
The average period only gives a rough starting point
Event number k is estimated from the year and must be an integer. The average time is only a starting point and cannot be regarded as the final date.
JDE₀ = A + kB
Added period correction to the original book
The orbit is not circular and is perturbed, and the original book uses multiple trigonometric corrections to push the mean time closer to the event.
JDE = JDE₀ + Σ periodic term
Configuration does not mean ensuring visibility
The conjunction may be too close to the sun to be observed, and the planets may not stop orbiting. True visibility also requires location, weather and horizon.
Geometric event ≠ observation guarantee
First select the planet and phenomenon, use A and B of the combination to determine the average event JDE₀, and then find the correction according to the corresponding period coefficient table. Different phenomena cannot share the same set of coefficients; the calculation time is TT, not local clock time.
give it a try
Select the elongation of Venus and the opposition of Mars to compare the geometry of Earth's perspective. Both the average and period corrected event times are given below.
No need to memorize symbols
- k
- integer event number
- JDE
- The number of consecutive days in the TT/original book TD time scale
- Δ
- Period correction to the average event time, in days
- large distance
- The angular distance between the inner planets and the sun reaches an extreme value
Algorithm, accuracy and scope of application
Realize the superior conjunction, inferior conjunction, east-west distance and two stays of Mercury/Venus; the conjunction, opposition and two stays of Mars/Jupiter/Saturn; the conjunction and opposition of Uranus/Neptune. Table 36.A and the trigonometric terms of each event are organized into coefficient data. The general summer is calculated according to T polynomials, and the inner planet's large elongation angle value is also calculated; the values are compared with the local AAPlanetaryPhenomena type by type and multiple k. Use the approximate formula in the original book, do not find roots through the current coordinates, and are not full-precision events; unsupported combinations are returned as not applicable. The picture is a geometric explanation, and the time can be deduced without using this indication.
my understanding check
Can the average event period itself substitute for a period correction?
cannot — The main method in this chapter is to add period correction to the average time, rather than just adding a fixed period.
When the outer planets oppose each other, how similar will it be to the Sun when viewed from the Earth?
opposite direction — The corresponding longitude directions differ by about 180°.
Can the event TT date be directly used as the clock time in your city?
cannot — Conversions such as time scale, time zone, and observation conditions are also required.
Define the phenomenon you are looking for first, then use the event number and period correction calculation; do not confuse one "close" with all events.
Jean Meeus · Astronomical Algorithms, 2nd ed. · No. 36 chapter
Planets and Small Solar System Objects · All interactive courses