Can someone please tell me how to properly quote your posts, so that I can answer them in the usual format? Thanks.
CurtC: Congratulations on the birth of your second son!
Greenwich Mean Time is used to calculate the planetary positions at the time of birth. This is because the ephemeris lists observed positions for 0-deg longitude – either at noon or at midnight, depending on which type you buy. So the point is that you have to determine what GMT was at birth and (essentially) interpolate planetary positions between the previous midnight (or noon) and the next.
True Local Time is used to calculate the position of the Ascendant (degree/sign on the horizon) and Midheaven (degree/sign directly overhead), as observed from the place of birth. Sidereal time is used for this, but corrections are made to account for the 4-min difference between the sidereal and solar day. This is also where latitude of birthplace comes into play. Then you consult a reference table – which usually lists the calculated Ascendant/ Midheaven positions every four minutes for each whole degree of latitude – and interpolate.
I’m not sure why you ask about partial-days – I mean, i understand you are referring to the fact that the solar year is 365.25 (or thereabouts) days long. But this has no effect on clock time – or dates, for that matter. The Gregorian calender itself corrects for this; it’s designed so that a particular astronomical phenomenon (the vernal equinox) occurs on the same calendar day, over the long haul. So every fourth year, the equinox occurs on the same calendar day and at about the same time.
Chronos: Good to know that I explained myself clearly.
RJKUgly: OP was correct about required info for a birth chart. Date of birth, time of birth (as nearly as possible) and place of birth (since both longitude and latitude enter the calculations).
Theoretically, yes: two children born at the same time in the same place have the same charts. Does this mean, theoretically, that they have identical personalities? Yes, at least at birth; but this does not mean they will remain exactly the same throughout their lives. A personality does not develop in isolation: environment and genetics plays a role. The inherent personality interacts with its environment, and is molded by it; and vice versa. Astrology does not say that the traits of the psyche are carved in stone and unchanging. But it does teach that every person is different, born with different inherent strengths, weaknesses, talents and traits. These may grow, change and alter through life – but the inherent, underlying persona is still there. Just as you grow physically, build bones and muscles, grow older, turn grey, lose your hair, etc. – your genes remain the same. You are still you, even if you are not exactly the same as you were at birth. There are still things about you which define you, distinct from everyone else. Two adults with the same chart would find that they share similar personality traits, strengths, flaws, etc. How these played out in their lives and experiences is an entirely different matter.
I know some people think that children are born as blank slates, upon which experience writes and gives them who they are. But what parent will argue that their children did not exhibit some degree of individuality, even in infancy?
As for matching charts to people: I think it should be possible, yes, but from a scientific perspective I see a few snares. For one, the natal chart is not an exact map of the adult with his/her cumulative experiences (see above). Also, matching a chart to the individual presumes that the individual is fully self-aware and in touch with him/herself enough to recognize his/her own description. This is not always going to be so; as someone observed much earlier in this thread, people often hear what they want to hear about themselves, not nec. what is true.
Sorry – have to dash to lunch but I will happily continue later on. And answer you more specifically about what kind of information the chart reveals.