The following C# code is to implement a rotation of a GameObject (e.g., planet). Just attach this script to an object and set two parameters (rotation w.r.t and speed).

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class Rotate : MonoBehaviour
{
    public Transform target;
    public int speed;
 
    // Update is called once per frame
    void Update()
    {
        transform.RotateAround(target.transform.position, target.transform.up, speed * Time.deltaTime);
    }
}

1. Create a new project from Unity Hub (Choose the Universal 3D Core [Not the one with Build-in Render Pipeline])
2. In the Unity Editor
3. Configure Build parameters: File → Build Settings: Check if the platform is correct.
4. Configure Project settings: Edit → Project Settings;
   • import 'TextMesh Pro' if you plan to use texts
   • import 'XR Plugin' if you are building a VR model
5. Import relevant assets: Window → Package Manager, select 'My Assests' and import the following assets (these assets can be purchased for free in Unity Asset Store)
   • Milky Way Skybox
   • Planets of the Solar System 3D
   • Simpler Kepler Orbits
6. Create a folder to store C# scripts: In the Project > Assests, right-click on the background and create a folder named “Scripts”.
7. Simulation background setting: Click the “main camera”, then Component > Rendering > Skybox. Then choose the Milky Way skybox in the “Custrom Skybox” panel.
8. Make the Sun (and set its rotate it)
9. Prpare for the Solar System Container: Since objects in this example are automatically created through the script “JPLOrbitLoader.cs”, we need to prepare a container and attach this script to the container.
   1. Create an empty, “SEM Container” and make it inactive (click the check mark off from the inspector panel).
   2. Create an empty under SEM_Container, “BodyTemplate”, with two child objects: “Velocity” empty and “View” sphere mesh.
   3. Create an empty under SEM_Container, “ScreenSpaceOrbitLineTemplate”.
      1. Attach “JPLOrbitLoader.cs” to SEM_Container and set the followings:
         1. set G-constant (6.67E-11)
         2. Scale_per_diameter (0.1)
         3. Body Template = 'BodyTemplate'
         4. Jason Data = <yourinput.json>
      2. Attch “TimeController.cs” and set default date/time
      3. Attach “ScreenSpaceOrbitsDisplay” and set
         1. Target Camera → Main Camera
         2. Line Template → “ScreenSpaceOrbitLineTemplate”
         3. Cam Distance = 0.7
   4. Attach “KeplerOrbitMover.cs” to “BodyTemplate” and set
      1. Velocity Handle = “Velocity” ←- the empty under BodyTemplate
      2. Time Scale = 1
      3. Lock Orbit Editing = True
   5. Attach “KeplerOrbitLineDisplay” to “BodyTemplate” and set
      1. Line Renderer Reference = “ScreenSpaceOrbitLineTemplate”
      2. Select desired Gizmo options
   6. Create UI canvas and panel with Input fields for YYYY/MM/DD HH:MM:SS, buttons (reset and set_time_now), and timescale input field and slider.
      1. Attach “TimeControlPanel.cs” to panel and set corresponding items to the UI objects.
      2. Check the Canvas Scaler setting: Resolution = 1280×1024
10. Click “Play” and you will see an animated Solar System objects showing orbital motions.
    1. Drag and drop 'Rotate.cs' on Sun Empty: set target (Sun Empty) and speed.