diff --git a/src/main.cpp b/src/main.cpp
index 2da5b2f..50bfd90 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -46,14 +46,41 @@
 #include "orbiter.hpp"
 #include "widget.hpp"
 
+// INPUT!
+//
+// what input do we even want in the first place?
+// * camera controls - this is a rendering only concern which needn't affect the orbital
+// * model validation - we want to modify orbits over time to confirm that our model is
+// working properly
+//
+// TODO: input can only be directly handled by static methods, so we need to find a way to collect
+// input from object instances and handle it at a higher level. in the case of this class, we want
+// to determine when a configurable key is pressed. alternatively, we can split the behaviour into
+// multiple sub-classes and run different loops at the top level?
+//
+// another idea is to process all input into a well-defined Input struct in the main loop, then
+// pass this struct into objects' render() method.
+//
+// it's possible the first idea makes the most sense if the plan is to ultimately extract the orbit
+// stuff to a library, since it keeps input a separate concern from the physics model
+struct Input
+{
+    bool cycleAnimation;
+} input;
+
 void keyCallback(GLFWwindow* window, int key, int scancode, int action, int mods)
 {
     if (key == GLFW_KEY_C && action == GLFW_PRESS)
     {
-        std::cout << "lol!" << std::endl;
+        input.cycleAnimation = true;
     }
 }
 
+void clearInput()
+{
+    input.cycleAnimation = false;
+}
+
 int main()
 {
     GLFWwindow* window = nullptr;
@@ -78,22 +105,29 @@ int main()
     Orbiter orbiter(orbiterSphere, orbit, unlitProgram);
 
     // register input
-    // TODO: init objects with a reference to the window so that they can register
-    // their own key inputs
     glfwSetKeyCallback(window, keyCallback);
 
     // Main loop
     while (!glfwWindowShouldClose(window))
     {
-        // TODO: receive input from GLFW
+        // receive input - key callback populates input struct defined further up,
+        // clearInput() needs to be called to clear input from previous frame
+        clearInput();
         glfwPollEvents();
 
+        // apply input
+        if (input.cycleAnimation)
+        {
+            orbiter.cycleAnimation();
+        }
+
         // rendering
         glClearColor(0.2, 0.3, 0.3, 1.0);
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
         float time = glfwGetTime();
 
+        planet.render(time);
         orbiter.render(time);
 
         glfwSwapBuffers(window);
diff --git a/src/orbiter.cpp b/src/orbiter.cpp
index ed53b31..6919843 100644
--- a/src/orbiter.cpp
+++ b/src/orbiter.cpp
@@ -1,13 +1,12 @@
 #include "orbiter.hpp"
 
-#include <GLFW/glfw3.h>
 #include <iostream>
 #include <astro/stateVectorIndices.hpp>
 
-Orbiter::Orbiter(Icosphere& sphere, Orbit& orbit, GLuint unlitShaderProgram) :
+Orbiter::Orbiter(Icosphere& sphere, Orbit& orbit, GLuint shaderProgram) :
     _sphere(sphere),
     _orbit(orbit),
-    _widget(unlitShaderProgram)
+    _widget(shaderProgram)
 {
 }
 
@@ -17,19 +16,29 @@ float Orbiter::getMeanAnomaly()
     return time;
 }
 
+void Orbiter::cycleAnimation()
+{
+    _animation++;
+
+    if (_animation > ANIM_ECCENTRICITY)
+    {
+        _animation = 0;
+    }
+}
+
 glm::vec3 Orbiter::getPosition(const float time)
 {
     std::vector<float> keplerianElements(6);
     _orbit.getElements(keplerianElements);
 
-    int animation = (int)(time/ORBITAL_PERIOD) % 2 == 1;
+    //int animation = (int)(time/ORBITAL_PERIOD) % 2 == 1;
 
-    if (animation == ANIM_ORBITING)
+    if (_animation == ANIM_ORBITING)
         return _orbit.getPosition(time);
 
     // TODO: i want to modify the eccentricity of the orbit with a control,
     // not an automatic animation
-    if (animation == ANIM_ECCENTRICITY)
+    if (_animation == ANIM_ECCENTRICITY)
     {
         // TODO: what are these magic numbers
         float e = .25 + .2 * sin(time);
@@ -40,7 +49,7 @@ glm::vec3 Orbiter::getPosition(const float time)
         return _orbit.getPosition(0);
     }
 
-    std::cerr << "unknown animation " << animation << std::endl;
+    std::cerr << "unknown animation " << _animation << std::endl;
     throw 1;
 }
 
diff --git a/src/orbiter.hpp b/src/orbiter.hpp
index afb7fda..bf48d6e 100644
--- a/src/orbiter.hpp
+++ b/src/orbiter.hpp
@@ -1,17 +1,22 @@
 #pragma once
 
+#include "gfx.hpp"
 #include "icosphere.hpp"
 #include "orbit.hpp"
 #include "widget.hpp"
 
+#include <GLFW/glfw3.h>
+
 class Orbiter
 {
 public:
-    Orbiter(Icosphere& sphere, Orbit& orbit, GLuint unlitShaderProgram);
+    Orbiter(Icosphere& sphere, Orbit& orbit, GLuint shaderProgram);
     ~Orbiter();
 
     void render(const float time);
 
+    void cycleAnimation();
+
 private:
     void updateModelMatrix();
     float getMeanAnomaly();
@@ -24,6 +29,9 @@ private:
 
     const float ORBITAL_PERIOD = 6.284;
 
+    // TODO: convert these to an enum
     const int ANIM_ORBITING     = 0;
     const int ANIM_ECCENTRICITY = 1;
+
+    int _animation = ANIM_ORBITING;
 };