Jupiters trojans from astronomy com.jpg
InnerSolarSystem with Asteroid and troja

Trojans - Jupiter's example:

"Trojans" are smaller Asteroids that have been "trapped" at the Lagrange Points L4 and L5 of Jupiter's orbit (explanation below). 
Other planets do have such "co-orbiters" as well but Jupiter got by far the most of them, as far as we know now. Interesting to note is, that these millions of asteroids form "families"....
Those points L4 and L5 are about 60 degrees before and after a Planet and explain the planetary Aspect of Sextiles and Trines in Astrology.

A "single" sextile aspect is bringing stability and is "smooth" - yet, one is ahead, just finished the start of a new cycle (orbit), needs to "grow creatively" and the other is about to finish a cycle, yet needs to start to discern and seeding for the future - both such Sextiles bring the feeling of safety and may feel as being "stuck" too but with the will for action....
A Trine brings stable harmony and a bit of "laziness" or the feel of "unnecessary to change"...  

Inner solar system. 

White is the Asteroide belt - the green dots are Jupiter's Trojans.

Trojandiagram by astronomy com.jpg

Astronomy: Roen Kelly after NASA/WMAP Science Team; Jupiter above: NASA/ESA/A. Simon (GSFC)

Lagrange Points:

L1 to L3 points were discovered by Swiss Mathematician Leonhard Euler  a few years prior to Joseph-Louis Lagrange discovered L4 and L5 in 1772 and was the "name-giver".

These 5 points are talking about the "gravitational" resonance of two bodies orbiting. Normally, the two planets/bodies exert an unbalanced gravitational force at a point, altering the orbit of whatever is at that point. At the Lagrange points, the gravitational forces of the two large bodies and the centrifugal force balance each other. Every planet has a set of these "points".    

Now imagine a line from L3 to L4 and to L5 - and from L4 to L5, but "cancel" the lines from L4 and L5 to the Sun (in Astrology those "center" lines aren't considered, maybe we should though) and you get a grand Trine as well as the so called "Kite", which I call a Pyramid (it looks similar to a tetrahedron).  Like L4, L5 and Jupiter (in this example) form the "basis" and L3 the "top"....   
 

Astrologically
Grand Trines brings very harmonious energies but often we "overlook" them, as we take the gifts of them as a given and miss to develop or grow them..... 

The Pyramid though, gives a little bit of "stress", challenge in the meaning of some form of activity/action, through the opposition. 
The themes provided by the Bodies at L4 and L5 (Sextiles) want to "move" but feel "trapped" (stress) but when integrating the middle Body-theme (Jupiter in picture) we can build a "foundation" to actually integrate the "Top"... with this, we can grow and "harvest" the gift here, which is freeing through growth....