A grand trine is three planets, points, or conjunctions all in trine aspect (about 120 degrees apart) to each other. It is called a "trine" because it forms an equal-sided triangle in the chart. More information is available here: http://www.bobmarksastrologer.com/GrandTrine15.2.htm
As to WHY you have so many in your chart, I believe it was because your birth could not be put off until another time when you would have had fewer!
4 fire grand trines! Whoah! That's... huge! Well to me anyways :roll:
Have you posted your chart here, Heaven? It would be interesting! I used to have a grand water trine, but supposedly the degrees are too far for it to be real...
Sincerely, I'm eager to see your chart!
All aspects are derivatives of the 360 degree circle divided by a particular number or "frequency".
A grand trine, is 360 degrees divided by 3.
The numerical vibration of the number "three" has particular qualities.
Too many to go into here, and out of topic anyway.
Sufice to say, the energy "flows" very smoothly.
However, it can be a real nightmare if it doesn't have a couple of oppositions and squares to level it out.
I did reading for a woman when I was first reading charts, a long time ago, and she had 3 grand trines.
I thought "Wow, this woman has got to be Mother Teresa herself!"
She was a total mess, had never had any boundaries imposed on her, had never learned any "real 3D" lessons.
She was a "Zillionair", and such a ...
Point being, "free flowing energy" is all good and well, but if it has no direction and no purpose, it is a good as any "bad aspect" can ever be.
It reinforces the theory that there are no good or bad aspects, only misunderstood, and miss-used ones.
If you place the slower moving planet on the ascendant, and see where the other planet lands, you can figure out the quality of the aspect...
The trine correlates with the 5th and 9th houses.
The lower trine (Leo) reflects a flow of juice that is concerned with the free flow of "self expression", so much fun!
The upper trine is connected with the free flow of "sharing", usually knowledge, but not restricted to it.
Grand trines are cool, but they sometimes need discapline...