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Recently, I was reading a paper in the MNRAS and the author casually referred to pointing their telescope toward the Sun-Earth L5 point. Now, I imagine working out where that is in the sky involves offsetting from the antisolar point by a fixed (slightly varying as our orbit is elliptical) number of degrees along the ecliptic, with the L4 being on the other side of the antisolar point. I looked at The SkyX and some other bits of astronomical software I have knocking about (including AstroPy) but have found none that will tell you the RA/Dec of the L4/5 points from a given location at a given time.
Does anyone know – offhand – what that offset is for the Sun-Earth L4/5 please? Alternatively, can you point me at some software that would?
I can only imagine that finding the Earth-Moon Lagrange points must be much harder.
L4 and L5 are almost exactly 60 degrees away from the Sun [*], along the plane of the ecliptic, I think?
I say “almost” because as you point out, the Earth’s elliptical orbit will presumably perturb that angle slightly over the course of the year, though I imagine the perturbation is tiny.
[*] — My original forum post was incorrect, so I have edited the wording.
A correction to my previous post. Seen from the Sun, L4/5 are both 60 degrees away from the Earth. Seen from the Earth, L4/5 are both 60 degrees away from the Sun.
The Sun, Earth, and L4/5 form equilateral triangles, with all three interior angles being 60 degrees, and all the sides being 1 AU.
Brilliant. Really hadnt realised you just had to look 60 degrees in front or following the sun. That makes it pretty easy, get the sun’s position on ecliptic in RA/Dec, convert to ecliptic cooords, add 60 degrees and convert back to RA/Dec again. Sure I can find something in AstroPy to do most of that. I imagine that drops it nicely into the edge of the Zodiacal light.
Thanks again.
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