# Earth's Orbit Path & Variations

Curiosity Science Physics Earth's Orbit Path & Variations

• Dear Geek Swipe,

Is there such a thing as a map, diagram, chart or a set of coordinates which define the ‘wobble’ of earth’s orbit through our solar system?

To put it another way, if we were to look at our solar system as a disk, earth’s path might be likened to the grooves in a vinyl LP.

These variations are measurable but are these figures available?

Many thanks, I look forward to hearing from you.

– Geoffrey via the Ask a science question page.

• Hello Geoffrey. Yes, all the planets in the solar system revolve around the sun close to a disk-like plane with a little inclination and eccentricity. For Earth, the orbital inclination is about 7 degrees related to the Sun’s equator. The eccentricity of the orbit is 0.0167. And you’re right, the orbit does change over time and this can be recorded.

And as we observe and record everything from the Earth, we keep our Earth’s plane as the reference plane and call it the ecliptic. We observe other celestial objects relative to this ecliptic. So, for the orbital motion of the Earth relative to Sun, we can simply track the Sun’s position throughout the year. The coordinate system is called the ecliptic coordinate system. It can either be geocentric like the above case or heliocentric.

And as mentioned, there will be significant changes in the orbit over a longer time—but like in thousands of years. As it involves other planets in the solar system, it’s an n-body problem. The orbital change will be due to perturbation effects. From planets like Venus and Jupiter heavily affecting the eccentricity of the Earth. The precession of the Earth. The axial tilt. And other complex orbital perturbations along with any unexpected celestial activity that affects the solar system. We call the cyclical effect on Earth as the Milankovitch cycles. Hope this is what you are looking for.

• Dear Karthikeyan KC,

However, these are the facts I already know.
My question was where do I find the data that tells us the actual positions of the earth during its varying orbits.

The earth’s position relative to the sun changes constantly, I rather assumed that these changes are measured and recorded.
It may be, however, that the earth’s wobbles month by month and year by year are too slight to be measured.

If you know about such data, I would be very grateful if you or the Geek Swipe Team were able to enlighten me.

All the best,

Geoffrey

• It may be, however, that the earth’s wobbles month by month and year by year are too slight to be measured.

@m1-6eek-5w1pe, you are right. The perturbations are too small if measured within a certain period of time. So for the long run, it is an iterative process where we will revise the celestial coordinate systems including all the perturbations at certain reference points in time. You might know these points as epochs.

I rather assumed that these changes are measured and recorded.

Yes, they are. And you can compute them for future dates as well. You can find them in an astronomical ephemeris. You can find one at NASA’s Solar System Dynamics website. But this one shows the data you need with J2000.0 as the reference epoch. For your case, you will need a similar calculator but one that uses up-to-date equinox data. Perhaps NASA’s SPICE is what you are looking for. Found a geometry calculator based on the SPICE data as well.

• Many thanks, this is what I was looking for.

SPICE didn’t show up in search results but then, I didn’t know the term, “astronomical ephemeris”.

I’ll hopefully find something that is at least approximate, that would be enough.