The Orrery Guide
Creating a System Orrery and in particular using the System Hierarchy Builder is a bit more complicated than other areas of Elite Galaxy Online. This guide aims to cover all you will need to know to use the new systems successfully.
Creating an Orrery
The first step in creating an Orrery is obviously to record all of the objects within a system here at Elite Galaxy Online. The quickest and easiest way to do that currently is to use the multi scanner to upload a batch of screenshots. Once this is done, orbital data for the planets such as semi major axis, orbital period etc is now known but there is one important piece of missing data, the system hierarchy.
When an object is recorded at Elite Galaxy Online, all information for that object is captured but the system has no idea about which other object in the system it is orbiting around. For example, if the Earth is recorded in the Sol system, it could theoretically be orbiting around the Sun, or around Jupiter or Saturn. There is no way of knowing from the recorded information alone and it is critical for the creation of the Orrery. This is where the System Hierarchy Builder comes in which is a new feature added as part of the 1.8 Orrery Update.
The System Hierarchy Builder can be accessed from the System View Page. There is a new “System Hierarchy and Orrery” section on this page which shows the current status of the hierarchy and gives access to the hierarchy builder as shown below.
Remember though that you must be logged in to access the System Hierarchy Builder. Creating system hierarchies can be a little tricky especially for complex systems with multiple Barycenters and as such I have deliberately made it so that any user can build/edit the system hierarchy for a system even if it is not one that they have recorded.
Using the System Hierarchy Builder
When you first launch the System Hierarchy Builder, Elite Galaxy Online will scan the system for any objects recorded in that system and display them across the scroll bar at the bottom. You can filter this scroll bar to just show Stars, Gas Giants or Planets and move it around by left clicking and dragging. Each celestial body in the scroll bar will have a button on it labelled “Add To Hierarchy” and when you click that it will be transferred into the main hierarchy builder screen.
Once a celestial body has been added to the main hierarchy builder you can drag it around by left clicking and dragging. Right clicking and dragging pans the entire view and the mouse wheel or middle mouse button zooms in and out.
To create a hierarchy relationship simply drag one body on top of another in the main hierarchy builder and a link will be created.
If you make a mistake, you can destroy a hierarchical relationship by dragging a body far enough away until the link snaps. Once all celestial bodies have been added to the hierarchy, click the “Submit Hierarchy” button to validate and complete the process.
If any errors have been found at this point you will be notified of the problem, or if everything is ok, the hierarchy will be submitted and the Orrery for that system created.
Every time you click the “Submit Hierarchy” button, the hierarchy is saved so if you need to come back to it later you can.
The video below shows an example of how to use the System Hierarchy Builder to build a simple hierarchy.
Building a Binary Star System
Research over the last two centuries suggests that half or more of all visible stars are part of multiple star systems so there is a good chance that when using the System Hierarchy Builder you will have to deal with Barycenters.
Whenever two bodies are orbiting each other, they always orbit around a common center of mass (the Barycenter). For situations where one body is much more massive than the other, for example when the Earth orbits the Sun, the center of mass is so close to the center of the more massive object that we can effectively ignore it. In these cases we can simply assume that the less massive object is orbiting around the center of the more massive one.
When two orbiting bodies are similar in mass, the center of mass will exist somewhere between the two bodies in space. For these cases, we need to account for the Barycenter. To understand when a Barycenter is needed, you can refer to the in game system map. As an example, below is the system map for Pru Euq ZN-A b55-0, a fairly simple system but which contains two stars that form a binary pair. The X which has been added marks the location of the Barycenter in this case.
Basically, in the system map whenever you see connector lines which connect two bodies in this way i.e. not in a straight line then you need to add a Barycenter.
To add a Barycenter in the System Hierarchy Builder you can simply click the “Add Barycenter” button which will create a new Barycenter in this system. From there you can drag it into the hierarchy in the normal way. The system will then automatically attempt to calculate the orbital characteristics of the Barycenter based on its position in the hierarchy.
The video below shows how you would build the System Hierarchy for this example of a Binary Star.
Building a Trinary Star System
When you start dealing with systems containing more than two stars, you have to start considering multiple Barycenter’s. For example, here is the System map for TR 24 Sector BW-U d3-12 B, a trinary star system containing no other planets or gas giants.
Again, I have added X markers to indicate the location of the Barycenters for this system. As you can see there are two barycenters within this system, a common center of mass for stars A and B which they will both orbit around and then a common center of mass for the whole system which Star C and the 1st barycenter will orbit around. Dealing with this kind of system in the System Hierarchy Builder is relatively straightforward as you will just need to add two Barycenters and arrange them correctly.
The video below shows the process of creating the hierarchy for the TR 24 Sector BW-U d3-12 B system.
Entering Data For Barycenters
Whenever you add a Barycenter to a system, the System Hierarchy Builder will attempt to calculate its orbital characteristics depending on various factors such as where it sits in the hierarchy, the mass of its child bodies etc.
However, there are two situations where it is impossible for the system to calculate the orbits until one piece of missing data is entered.
The first of these situations is when the Semi Major Axis of the Barycenter cannot be calculated. An example of this can be seen in the Schee Hypue NT-O d7-4 system as shown below.
The Schee Hypue NT-O d7-4 system contains a single class F Star with 7 planets but the 3rd and 4th planets are actually orbiting around their common center of mass. The X marker in the image above indicates the position of the Barycenter in this case. It’s important to understand that for cases like this, when we look at the actual orbital data which has been recorded for the 3rd and 4th planets, it is all stated relative to the Barycenter which these objects are orbiting around.
For a case like this, there is no way of knowing the exact semi major axis of the Barycenters orbit around the main star and this is where some data entry is required. When the System Hierarchy Builder detects this kind of situation a new button will appear against the Barycenter allowing you to enter this measurement of Semi Major Axis in Astronomical Units.
The simplest way I have found to do this is to compare the semi major axes of the other planets in orbit around the main star. For example, in this system, the second planet has a semi major axis of 1.33 AU and the 5th planet has a semi major axis has a semi major axis of 2.29 AU. We therefore know that the Barycenter for the 3rd and 4th planet has to lie somewhere between this range say for example 1.8 AU.
Whilst this method is only an approximation it gives good results which are fairly accurate. If you wanted to get really detailed you could fly your ship out to the system and start making more detailed distance measurements but whether this is an engaging thing to do remains to be seen 🙂
Once you have entered the semi major axis for these kinds of Barycenters, the System Hierarchy Builder will be able to calculate the Orbital Period and model the orbits.
The video below shows how to use the System Hierarchy Builder to deal with this problem.
Entering Separation Distance For Barycenters
The second situation where a small piece of data entry is required for Barycenters is when you have two Barycenters which are orbiting around each other. As an example, lets look at the Synuefai WE-Z b43-0 B system which contains 4 stars as shown below.
Again, I have marked the location of the Barycenters with an X on the map and you can see that in this case we have 3 individual barycenters and two of them are orbiting around each other. This is perhaps the most difficult of situations for the System Hierarchy Builder to deal with as we have very little information to go on in this case.
When the system hierarchy builder detects this situation, a new button will appear asking for the total separation distance of the two barycenters in AU. When you enter this piece of data, then the system will be able to calculate the individual orbital periods and semi major axes and an Orrery can be generated.
Unfortunately, I have not been able to figure out a good way of determining this separation apart from measuring it out there in the black with your ships instruments or by estimating it from the other information available. In this example if we look at the individual semi major axes for the stars we have the following:
- A – 0.25 AU
- B – 0.87 AU
- C – 2.52 AU
- D – 6.30 AU
Given that star D orbits around the common center of mass with Star C with a semi major axis of 6.30 AU, I would want the total separation between the two barycenters to be at least that amount. In this case therefore, I can estimate say 10.0 AU.
If there’s any astrophysicists out there who perhaps have some more insight into orbital mechanics and this problem, please get in touch!
The video below shows how the system hierarchy for this more complex system can be constructed.