# RA and Dec of L4 and L5

1. Oct 18, 2004

### Valareos

Does anyone know the JNow Ra and Dec of the L4 and L5 points in the Sun/Earth System?

2. Oct 22, 2004

### BrianJ.

Hi,
interesting question, can't find any references on the web, so here's a couple of thoughts.....

My understanding of the Earth/Sun L4 & L5 points is that they lie on the Earths orbit with the lines linking them to the Sun making 60° angles with the Earth-Sun line. So Earth/Sun/L4 and Earth/Sun/L5 are equilateral triangles (when viewed from above the plane of the ecliptic). So, L4 must be 60 degrees East of the Sun and L5 60 degrees West, along the plane of the ecliptic. So if you know the RA and Dec of the Sun, you've got a good start! (Have a look at JPL Horizons website,that should give the Sun RA and Dec for given time). Then the question becomes one of trigonometry....how to calculate the position of a point 60 degrees East(or West) of the Sun along the plane of the Ecliptic which is inclined at 23.45 degrees to the celestial sphere equator.
My trigs not that good, unfortunately! Anyone?.......

NB This assumes the Earth's orbit to be circular, which it isn't, so this is only an aproximation, I guess......

Good luck,
BrianJ.

3. Oct 22, 2004

### MiGUi

Lagrangian points are actually ellipses around the Sun. They are always over an imaginare line from the Sun to our planet. ¿Can have RA and DEC, those imaginary orbits? Difficult to calc...