### How to calculate a planet's current position within the solar system

• I'm making an application that needs to calculate a planet's current position within the solar system - I don't want to calculate its position in the sky.

For example, what I want to do is exactly what this website does:

http://www.theplanetstoday.com/

I want to create an overhead view of all the planet's positions in the solar system.

Where do I start? Is there a latitude/longitude coordinate system for the solar system? Everything I've found seems to calculate a planet's position in the sky from the observer's point on earth.

As the page you mention itself notes, http://ssd.jpl.nasa.gov/horizons.cgi (HORIZONS) has all the data you need. If you want to make your own computations, NASA publishes formulas that describe planets' positions to within a few hundred meters.

Thanks barry, this is exactly what I needed. By using the vector ephemeris type HORIZONS calculates the x, y, and z coordinates of planetary bodies relative to the sun. If I need to dig deeper into it I'll use Gerard's answer, but for now this should do.

• Buy Astronomical Algorithms 2nd ed. by Jean Meeus. It is published by Willmann-Bell Inc. If you buy it direct from the publisher, you will get a corrected printing with all errata up to August 10, 2009. There are a number of systems for describing the location of a planet. This book provides a method to find the heliocentric longitude, latitude, and distance from the Sun. It also explains the different coordinate systems and how to transform from one to another.

The method you use depends on how accurate you need to be. If you state your needed accuracy some of us might be able to suggest other alternatives.

Can you describe the relevant information?

The book has 58 pages of coefficients, and an explanation of how to combine the coefficients to find the positions. There are other sources that are shorter but less accurate, or (much) longer but less accurate.