A is the the first letter of the Sanskrit, Latin and English Alphabet. It corresponds to Alif in Arabic, Alpha in Greek and Aleph in Hebrew. In some early alphabets the first letter is merely a point or 3 points in the form of a bindu.

In Sanskrit A is much more than the first vowel. In AUM
A = Beginning   = adimat     = Creator     =  Brahma
U=  Progress     = utkarsa    = Preserver  =  Vishnu
M = End            = miti          = Destroyer =  Shiva
See: AUM and adimat, utkarsa, miti. Cf. Alpha - Omega.
A - K
The complex origins of this letter are almost certainly linked with the symbol for Agni which was  sometimes ^ and sometimes an upward triangle. Greek and some versions of the Latin Aphabet reduced the A to ^. This analogy of A and flame leads not only to Agni but also to reconsider the link between A and K.
Morning      A     
Noon          >     becomes  >I   becomes K, becomes AK and becomes ac.
Afternoon   KA                                      
In the afternoon this AK is reversed as KA. This leads to "aka" the word for 1 and Akka as in Akkadians and accadians. See: 3 Phases of Day.
A Ka Tha (q.v.)
In the context of the "A Ka Tha" it is the beginning of the creative process as the original trinity which was upight in the form of an upward triangle moves downward in the form of a downward triangle. A Ka Tha also leads to a sequence
 A K 
 A K T 
 A K T P 
These letters become the names of divisions of the Sanskrit alphabet and alphabets generally
A - L
When the logic of 3 phases of the day is applied to three seasons of 4 months each then we have:
Spring        A     
Summer     Λ
Autumn      V
This logic explains why A and L are fundamentally connected. If we take 3 L shapes and connect their apex at 120 degree intervals we have a Triskell. If we take 4 L shapes and connect their apex at 90 degree intervals we see a counterclockwise swastika. This form goes back at least 18,000 years and was called Yungdrung (q.v.).  
Focussing on the first 2, in terms of the year:
First 6 months =  A       = Alpha  
Last 6 months =  Λ       = Lambda
Visually this means A shift from A with full power to A with reduced power.
First 6 months =  AΛ  = AL
Last 6 months =  ΛA   =LA
This leads to obvious combinations:
Male      Female
AL         LA 
Al          Lat         
Al          Allat
See: AL -LA

A-G    H-N     O-U     V-Z
When we apply this approach of phases of time to the week then find:
Week 1 : Days 1 - 7:    A - G
Week 2 : Days 8- 14:   H - N
Week 3 : Days 15- 21: O - U 
Week 4 : Days 22- 26: V - Z
Day 14:  N
Day 15:  O  = Full Moon, the O of Ovum and YOni
Day 16:  P   = Full Moon where Male I and female o become P with
                     metaphysical dimensions in Nitya 16 and mystical drop.
The first week goes from A to G.
G = Guru (later Jupiter) becomes the Male. 
The end of the first week after A-G brings a split to a second week which is shown by H, which becomes hera or hIra and becomes the female.
These are then aligned:
Left              Right
Male             Female
G                 H
Guru            hera/hIra
Zeus            Hera
Jupiter          Juno

A remains male. So we have further connections of A -H
Male            Female
A                 H 
ha               Lha        
Ha               Hu
Hahut          Lalut
Ha              Ya      
Ha              Haya
Am             in
Amin          Haya
See further under A - H  and H -Y
A-M             N-Z
In terms of the year, there is a split between the first 13 letters A-M and the second 13 letters N-Z. See: Male - Female Letters 
A -V
Seen as a flame A begins as an upward flame linked with 3 phases of a day, the flame begins upwards, turns sideways and is then  inverted as V:
Morning      Λ 
Noon          >
Evening      V
This leads to Sanskrit words which have become familiar elesewhere:
Focussing on 1 and 3, in terms of the year
Beginning of year           = A
End of Year                    = V
But there is a challenge of expressing that the year continues, so
Beginning of year           = A
End of Year                    = Y
The end now points to a bifurcation which implies a new beginning and new life. In Sanskrit this leads to the words:
aya    =   turn to right (in chess and of the sun assuming one looks East)
Aya    =   approach
aja     =   goat, ram, Aries
The implications of this shift go much deeper.
They help us understand why
AUM is fundamentally linked with
See: A - Y.
In an older Hindu system the year began with Sagittarius which was placed in the bottom left of a cube of 16 squares (see Presentation Zodiac Square). In these squares the orientation was to the East at the top. As a result the year divided as follows:
First 6 Months                                        Last 6 Months
Mid-November - April                             Mid-April - End of October 
Sagittarius- Aries                                   Taurus - Libra
Γ                                                          Γ    Reversed  
Γ   =  G or Ga as in Gamma                    Γ    Reversed   = Ag
G - A                                                    A - G
gama                                                    agama
guna                                                     aguna   or
G - A                                                    Y - A
Ganges                                                 Yamuna
See: Ganges -Yamuna
Further Notes.
In hieroglyphs A as Ah is linked with Vulture and broad A is linked with Arm and Hand.
In Sumer according to Encyclopedia Britannica 1911:
The word a= the sign A =  water  (original meaning) can indicate anything whatever connected with the idea moisture. Thus, water, moisture, weep, tears, inundate, irrigate, &c. The word a can also mean  shining, glistening, an idea evidently developed from the shining rippling of water. Note that in Turkish su means both  water  and  the lustre of a jewel, while in English we speak of gems of the first water. The combination a-and-tu, literally  water enter ship, means abetbu,  deluge, ordinarily, but in one passage a-md-tu is made the equivalent of shabilbu,  flame, a pure pun on abilbu,  deluge.
See Website.
Saturn = A = 1
as first of the 7 Vowels:  A E H I O Y Ω

In the All Powerful Ten A is implicit and refers to the Green Space Circle around the Mandala.
ओ - औ