The Need for Many Limits  A single fixed meridian limit is not usually optimal because while it may provide the maximum meridian travel at a single declination, it might be limited at another declination where the mount could track farther past the meridian. For example, when declination is near 0 degrees, the scope can usually pass underneath the mount without any possibility of collision. However, as the scope's declination moves further away from 0, the telescope can start to protrude enough that it can strike the pier under certain circumstances. There is a tradeoff between simplicity (setting one limit and being done with it) and optimizing how your mount handles meridian flips so it can track longer without needing to flip.

 

 

 

Meridian Limits and the Horizon  In situations where the scope will not hit the pier, the limiting factor becomes the horizon.  Take note that in observatory settings, this horizon can differ significantly in its Alt and Az values from the horizon values you established earlier with the Horizon Limits Editor.  The following two screens - both identical views, and both at a declination of 10 degrees - show this difference:

 

The Meridian Tracking Limits Explorer helps you setup custom meridian tracking limits for each declination.  You record a series of limit values, and the Explorer interpolates a full curve from these points to give you defined limits throughout the sky.  The Meridian Tracking Limits Explorer Window is shown below. To access this screen, click on Edit to the lower right of center on the Meridian Tab.

There are five ways to build your meridian limits curve with the Explorer:

1.Use the Set Constant Limit to create a fast, simple fixed limit for the entire side of pier. Constant limit value is entered in Hour Angle (e.g., a value of "1.00" is 1 hour or 15 degrees). When you press the Set Constant Limit, it will create the limit on the West side. If you wish to set a constant limit on the East, you will first need to create it on the West, then "Reflect West" to copy it over to the East, and then you can change your West limit if desired.

2.Use the Explorer's semi-automated method for drawing the limit curves.  This method is detailed in the Using the Meridian Tracking Limits Explorer sub-section (next section) of this Help file and involves steps 1 through 3 as shown in the screen shot above.

3.Draw a limit.  This is performed just like drawing a custom Horizon Limit - by clicking and holding the left mouse button while you trace out your limit.  This is NOT recommended unless you are very familiar with meridian limits and how they should look.  It is really most useful as a way to quickly modify an existing limit curve to reflect a minor change in the limit determining factors.

4.Manually Add Points.  Clicking on the Manually Add Points button on the lower right side of the Explorer Window will open up the Add Meridian Tracking Limit window.  This will be detailed in the Manually Add Meridian Tracking Limit Points sub-section below.

5.Edit the Table Manually.  You can go into the actual interpolated data table of an existing Meridian Tracking Limits curve and edit the values at each meridian inclination.  This is also recommended only for advanced users.

In addition, please note the following:

•There are some instances and situations where you may wish to combine the methods above.  The simplest example is tweaking a mapping done with the Explorer using the "draw" feature.

•The two Reflect buttons can be a HUGE time saver. It "reflects" the data points on one side of the meridian to the other. This is useful when your telescope is symmetrical (single scope) instead of a side by side configuration with two different telescopes

•The More button allows you to Copy East to West, and Copy West to East. These are different operations than Reflect. These copy the values from one side to the other side of pier. This will force the mount to always flip at a declination's meridian limit at the same hour angle regardless of which side of pier the mount is on.

•The screen shot below is provided to further explain the graphical representation of the limits shown in the Meridian Tracking Limits Explorer (labeled as Step 3 - Define Meridian Tracking Limit Points).  It shows the graph as it would look part way through a typical meridian limit mapping run using the Meridian Tracking Limits Explorer.