nbelakovski / asen_6008

Constants for CU Boulder's ASEN 6008

About

This library encodes all of the information provided in the handouts Coefficient Data and Ephemeris_Meeus from ASEN 6008 (CU Boudler). This library was created in Spring 2021 when the course was taught by Professor Kate Davis. The relevant files have been uploaded to the repo.

Installation

pip install asen_6008

API

This library provides 10 classes (the 8 planets, Pluto, and the Sun) and 2 constants, AU and Days_per_year.

The classes are all instances of the class Planet which has the following layout (note this is pseudocode)

class Planet:
    L # deg
    a # AU
    e
    i #deg
    Omega # deg
    Pi  # deg
    mu  # km3/s2
    r # km

Elements L, a, e, i, Omega, and Pi are of type OrbitalElement which has the following layout

class OrbitalElement:
    a0
    a1
    a2
    a3

Elements mu and r are simply floating point values.

To access any of the data for a planet would look something like this

import asen_6008

print(asen_6008.Mars.L)
print(asen_6008.Earth.e.a1)
print(asen_6008.Sun.mu)

The names of all the classes and constants provided are listed below

AU
Days_per_year
Sun
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto

Also, both the Planet and OrbitalElement class have overridden the __repr__ class attribute, so they can be printed directly, for example:

>>> import asen_6008
>>> print(asen_6008.Jupiter)
L (deg): 34.351484, 3034.9056746, -8.501e-05, 4e-09
a (AU): 5.202603191, 1.913e-07, 0, 0
e: 0.04849485, 0.000163244, -4.719e-07, -1.97e-09
i (deg): 1.30327, -0.0019872, 3.318e-05, 9.2e-08
Ω (deg): 100.464441, 0.1766828, 0.00090387, -7.032e-06
Π (deg): 14.331309, 0.2155525, 0.00072252, -4.59e-06
μ (km3/s2): 126686536.1
r (km): 71492

Usage

Because the professor requested that no equations be placed in the library, only constants, the user will have to supply their own equations for calculating the ephemeris information as a function of time. There are many ways to do this, but one way which leads to a fairly clean API is to wrap the classes provided in your own class, like this

import asen_6008

class MyPlanet():
    def __init__(self, planet):
        self.planet = planet

    def e(self, t):
        return self.planet.e.a0 + self.planet.e.a1 * t + self.planet.e.a2 * t**2 + self.planet.e.a3 * t**3

Earth = MyPlanet(asen_6008.Earth)
Mars = MyPlanet(asen_6008.Mars)

print(Mars.e(some_julian_date))

You'll want to put this class and the instance of it in a separate file that you then import into your main Python project.

This way you can access various properties of the planet with a simple interface that accepts a time value. But you can also reach in directly to the underlying class provided by the asen_6008 library, as follows:

print(Earth.planet.e) # Here Earth is the same instance that was defined above.