The Big Dipper and the North Star, symbols of the Celestial Mechanism 
Trigrams Qian (Heaven) and Kun (Earth)
A salmon swimming against the stream, returning to the source
Ten oxherding pictures 
Hexagram #1 Heaven
An Egytpian representation of the Yellow Woman or Mysterious Female— the goddes Hatthor (also called the primordial Mother Goddess) with the narrow gate on her head
The Celestial Mechanism
The I Ching is a book about the Celestial Mechanism.
-- Lu Dongbin (9th c. Taoist master, introduction of The taoist I Ching)
The ancient maxim as above, so below attributed to Hermes Trismegistus (purported author of the Hermetic Corpus) refers to the idea that the principles of the macrocosmos universe are mirrored in the microcosmos man.
This idea is part of all esoteric traditions and plays an important part in the inner meaning of the I Ching and the 2nd century Taoist text Canton Qi (Triplex Unity)
Because the Firing Times of controlling the human mind or lower self — the stripping away of mundane yin — and bringing out the Original Spirit or Higher self — creating pure yang — are symbolized in various movements of the heavenly bodies, it is also called the Celestial Mechanism.
-- Liu Yiming (The Inner Teachings of Taoism)
These various cycles of heavenly bodies have different durations, but actually symbolize the same thing.
The Big dipper traveling around the North Star, the waxing and waning of the moon, also called the firing times of the lesser circuit of the sky, and the circulation of the sun, also called the firing times of the greater circuit of the sky, all symbolize the firing times. The times of the firing are represented by different trigrams and hexagrams.
The Big Dipper
When young I mastered the paths of life and death.
I visited all the great teachers who taught me their Way
I took Heaven as my roof and the Earth as my furnace
And used both kinds of medicine to complete the sun and moon,
Taking from yin and yang, joining Fire and Water,
I relied entirely on the Dipper for success in my movements.
-- Journey to the West, Ch 70
-- Wei Boyang (2nd c. Taoist master, Cantong Qi)
The Head (kui魁) refers to the four stars of the dipper, and Handle (bing 柄) to the last three stars of the Dipper. In ancient times man would navigate according to the position of the stars at night. The stars guided one to one`s destination. Internally this refers to the breaths of the firing process guiding one to one`s internal destination; the presence of the Original Spirit. A star is after all, a sun, and represents fire, which symbolizes the illumination of conscious awareness. The three stars of the dipper handle relate to the firing times to create the pureness of three yangs, the trigram Qian (Heaven) ☰, which is an abbreviation of the hexagram Qian (Heaven) ䷀ and are represented in the first six oxherding pictures. The four stars of the head relate to four immortals breaths and are represented in the last four oxherding pictures.
-- Chao Pi Chen (20th c. Taoist master)
The Moon — The Lesser Circuit of the Sky
All esoteric traditions see the moon as a symbol for liberation.
-- Ouspensky (20th c. Fourth Way teacher)
As said above, the trigrams Fire (Sun) ☲ and Water (Moon) ☵ are not part of the firing process. The six trigrams that make up the firing times have a natural ebb and flow from one yang to three yangs and then returning from one yin to three yins. Fire and Water take charge of these six trigrams and are the medicine; yin and yang; the inhalation and exhalation of the breath; they are not part of the cycle of the moon. The crescent moon is symbolizes by the trigram Thunder ☳ and hexagram # 24 Return ䷗.
The Cycle of the Moon -- Wei Boyang (Cantong Qi - Triplex Unity)
Thunder ☳ comes forth as an inkling,and the Yang Breath makes it start:
“Initial nine, submerged dragon.”
On the third day Thunder ☳ moves,
on the eighth, Lake ☱ is in action.
“Nine in the second place, appearing dragon”
On the fifteenth, virtue is attained
And the body of Heaven ☰ is achieved.
“Nine in the third place, at nightfall he is watchful,”
fearing that he might lose the magic charm.
When Wind ☴ takes control,
it firmly holds it in his hands.
“nine in fourth place, wavering flight”:
Mountain ☶ rules over arrest and advance,
On the twenty-third day,
it presides over the waning quarter.
“Nine in the fifth place, flying dragon”:
sitting in the throne of Heaven, it increases it`s delight.
On the thirtieth day, Earth ☷ inherits the charge,
Carrying and nourishing her children,
She is like a mother to all things in the world.
“Nine at the top, thriving dragon,”
The use of the dragon-nines flying to and fro,
are the compass and square of the Dao.
The Yang numbers are now completed.
The Cycle of the Moon symbolizes the creation of the Golden Elixir by using six trigrams. Each trigram is a step of the Firing Times going from one yang ䷗ to the pureness of six yangs, when the hexagram Qian (heaven) ䷀ is reached.
Logically this does not make sense, since from the fourth trigram on, yang begins to decrease and returns to yin with the sixth hexagram. However, as Yuyan said above it is all metaphor. The symbols of inner alchemy have the same purpose as the koans of Zen-Buddhism, which is to bypass the logical mind and inspire and awaken the Original Spirit.
The Sun — The Greater Circuit of the Sky
While the cycle of the moon uses the trigrams, the cycle of the sun uses the hexagrams to symbolize the creation of the Golden Elixir.
Ancient immortals used the term Gold Elixir as a metaphor of the essence of true consciousness...... Growing from one yang to gradually reach the pure wholeness of six yangs, growing from vague to clear, the Gold Elixir develops naturally. -- Liu Yiming (Inner Teachings of Taoism)
The Cycle of the Sun -- Wei Boyang (Canton Qi - Triplex Unity)
At the new moon`s light lies Return ䷗;
The Yang breath begins to spread through,
Going out and coming in without error.
At Overseeing ䷒, the furnace issues strips of light,
Opening the way for proper radiance.
Radiance and shine gradually advance.
Looking upward, it forms Tranquility ䷊.
The firm and the yielding both come to hold sway.
As Yin and Yang conjoin,
The small departs, the great approaches.
Gradually comes the turn of Great Strength ䷡.
Boldly standing at the gate to dawn.
At Parting ䷪ the time has come for Yin to move into retreat,
For Yang has risen and has come to the force.
Heaven ䷀ is strong, flourishing, and bright,
And lays itself over the four neighbourhoods.
Here, pure yang has been reached and the Golden Elixir is created. The verse then continues with six hexagrams (Meeting ䷫, Withdrawal ䷠, Obstruction ䷋, Observation ䷓, Stripping Away ䷖ and Earth ䷁) showing the ascend of yin and descend of yang.
These hexagrams represent mundane yin energy arising, pure yang energy being injured and consequently the loss of the Golden Elixir. When one observes this in oneself, one tries to interrupt this process and return to pure yang again. The end verse of this section is as follows:
Taoist master Shangyang comments on this:
Now these twelve hexagrams are seen from a different perspective. The two groups of six hexagram (six hexagrams of advancing Yang and six of advancing Yin), if they gain the Yellow Woman, actually represent the inhalation and exhalation of the six yang breaths of the firing process.
The yang of Heaven and the Yin of Earth are like the opening and closing of a door….. Opening and closing, breathing out and breathing in, are the door of the mysterious female, the root of Heaven and Earth. Here breathing out and breathing in do not refer to exhalation and inhalation through the nose, but rather to the opening and closing of the true breath, the inner pulse of life, the movement of energy and stillness of the spirit. -- Li Dao Chun, the Book of Balance and Harmony p48
The first verse about the return of Yang said: The Yang breath begins to spread through. After one has reached the pureness of six yangs, meaning a pure state of conscious awareness, one does not want to return to yin intentionally. In fact, the hexagrams following #1 Heaven, Hexagram #44 Meeting, #33 withdrawal , #12 Obstruction, #20 Observation, #23 Stripping Away and #2 Earth, are all about how to ward off yin energy.
-- Liu Yiming (The Taoist I Ching, hexagram #44, commentary on the top line.
The Firing Process and the Celestial Mechanism are intentionally not completely explained.
In the Taoist I Ching, Liu Yiming mentions about fourteen times that the firing process cannot be known on one`s own; one needs to find a genuine teacher.
The cycle of the sun takes twelve months; each hexagram is matched with a month. However, Taoist scriptures repeatedly speak of ten months of work, not twelve months.
The Chinese use the lunar calender, where one month is four weeks, so a pregnancy is considerd to be ten months. The number ten is what is important here. All the symbolic cycles of the Firing Process come down to ten breaths.
One needs to continue: The spectacle of an hour appears within a whole breath. Any single breath contains within itself the ‘catch’ whereby the single yang returns.
The Firing Process refers to six breaths of action and four breaths of non-action in which one bathes.
-- Zhuangzi (4th c. BCE Taoist master)
-- Chao Pi Chen (20th c. Taoist master)
The Big Dipper God Tonrosho
Trigrams Li (Fire) representing the sun and Kan (Water) representing the moon, symbolize the medicine
The sheperd boy with the Big Dipper (ninth picture of the ten oxherding pictures
Sun Wukong, The Monkey King 
Hexagram #24 return and hexagram
Venus of Willendorf, estimated to have been carved .24,000–22,000 BCE. She is a symbol of the Earth Mother or Mother Goddess that can be found in all esoteric traditions.
In Taoism she is called the Yellow Woman 
The laughing Buddha, pregnant with the spiritual embryo
