Finding and Displaying Eclipses



In the OverView section, several figures showed that both solar and lunar eclipses could be found and displayed using Rendezvous.  In the following sections, I'll give you a step-by-step tutorial on how this is done.

How to Find Eclipses

Finding eclipses is quite easy with Rendezvous.  For our tutorial here, we will find all the solar and lunar eclipses during the year 2000.  All the controls necessary to do this can be found in the Eclipse Prediction panel.  To display the panel, click the Event Prediction : Eclipses button in the main menu.  The following panel appears:

In order to find all the eclipses between January 1, 2000 and January 1, 2001 follow these steps:

Set the start date:

o Select the Start button directly above the Calendar.
o Use the right/left arrow button to set the year to 2000
o Use the right/left arrow buttons to set the month to January
o Click on the date 1 in the calendar

Set the start time:
o Double-Click in the hour field of the clock.
o Type the value 0, then hit the tab key to move to the minutes field
o Type the value 0, then hit the tab key to move to the seconds field
o Type the value 0, then hit the return key.

Set the end date:
o Select the End button directly above the Calendar
o Use the arrow buttons to set the year to 2001
o Use the arrow buttons to set the month to January
o Click on the date 1 in the calendar

Set the end time:
o Double-Click in the hour field of the clock.
o Type the value 0, then hit the tab key to move to the minutes field
o Type the value 0, then hit the tab key to move to the seconds field
o Type the value 0, then hit the return key.

Now the Start and End dates have been selected and we're ready to find the eclipses

o Click the Find button at the bottom of the panel.

Rendezvous begins searching for the eclipses.  When it is done, the panel displays the following results:

We have four solar eclipses and two lunar eclipses, quite a year!  Double clicking on any of the entries loads the eclipse Begin Date and Time into the main window for display.  Let's look at the Solar eclipse on December 25, 2000 in detail.

Displaying the Lunar Shadow During a Solar Eclipse

During a solar eclipse, the moon passes between the earth and the sun, and casts its shadow over a portion of the earth.  We can display the shadow by following these steps:

o Double click on the entry for the Solar eclipse on the date 2000-12-25 in the Eclipse Prediction panel.
o Bring up the map inspector by clicking on the Inspectors : Map... button in the main menu
o Select the Lunar Shadow option button in the Options area of the MapInspector panel.

The shadow will now be visible as we advance the clock.  When you complete the first step above, the date in the Calendar in the main window will be set to December 25, 2000 and the clock will be set to 15:22:28.  We can now advance the time by one hour:

o Click in the hour field of the clock in the main window
o Click on the up button next to the clock

We can see the shadow of the moon across North America:



Displaying the Solar Obscuration by the Moon During a Solar Eclipse

Now that we can display the lunar shadow, let's try displaying what the actual obscuration of the sun by the moon would look like from, say, Des Moines Iowa.  We can do that by following these steps:

Load the USCities.gnd file into the Sensors browser:

o Click on the Constellation : Open Sensors button in the main menu
o Navigate to the USCities.gnd file
o Select the AutoDetect entry from the Platform pull-down button
o Click the OK button at the bottom of the panel
o Click on the USCities entry in the first column
o Double-Click on the DesMoines, IA entry in the second column

Load the Sun and Moon into the Targets browser:
o Click the Constellation : Open Targets button in the main menu
o Navigate to the PolynomialPlanets.list file
o Select PolynomialPlanet from the Platform pull-down menu button
o Click OK at the bottom of the panel

Select Sun and Moon targets:
o Click the PolynomialPlanets constellation in column one of the Targets browser
o Double-click the Sun entry in column two of the Targets browser
o Double-click the Moon entry in column two of the Targets browser

Your main window should now look like this:



Bring up the Telescope Inspector:

o Click the Inspector : Sensors...  button in the main menu.

This action brings up the following panel:

We want our sensor's telescope to track the sun, so we need to swap a TrackingAttitude subclass into the Attitude processor, and select the Sun as our tracking target:

o Click the InertialAttitude button and drag it down to the TrackingAttitude selection.
o In the Detail area of this panel, select the Telescope button.

The Telescope Inspector panel now comes up.

o Double-click the entry Sun in the Targets browser of the Telescope Inspector Panel (which is now titled DesMoines, IA)

Our telescope is now tracking the sun.  The sun will stay centered in the boresight crosshairs as we change the time.  Notice though, that the sun is just a little tiny dot in the center of the view.  We can zoom in on that using the Field of View Extent textfields like this:

o Type the value -0.8 degrees (notice the negative sign in front) into the Az Min text field of the Field of View Extent, and then type a tab character to advance to the Az Max textfield.
o Type the value 0.8 degrees into the Az Max text field, and type a tab character to advance to the El Min field
o Type the value -0.8 degrees (again, notice the negative sign) into the El Min field, and type a tab
o Type the value 0.8 degrees into the El Max field, and type a carriage return key.

The Telescope Inspector panel should now look like this:

If we advance the clock in the main window by one minute at a time, we can watch the moon in the Telescope Inspector as it passes in front of the sun, just as it will appear to viewers in DesMoines Iowa on December 25, 2000.

Displaying Lunar Eclipses

This section assumes you have performed all the steps in the Eclipse Tutorial up to this section, and Rendezvous is still in the same state that it was at the end of the previous section.  Let's now watch the moon pass into the shadow of the earth during the lunar eclipse of January 21, 2000 as it is seen from Des Moines Iowa.  Perform these steps:

Select the Lunar eclipse:

o Double click on the entry which has 2000-01-21 as the Begin Date in the Lunar eclipse section of the Eclipse Prediction panel.  The main window's date and time will be set to this entry's date and time.

Set the tracking target to be the Moon:
o Double-Click on the Moon entry in the Targets browser of the Telescope Inspector panel.

Increment the clock in the Main Window a few minutes:
o Click in the minutes field of the clock in the Main Window, and increment the minutes field to 20.

As you increment the clock, you should see the moon begin passing into the earth's shadow.  At the time 3:20:12, the Telescope Inspector should look like this:

The shadow of the earth is covering the "southwest" corner of the moon.  The azimuth and the elevation of the boresight tells us where we should look in the sky.  The inspector shows an azimuth of 105 degrees which is in the eastern sky (actually a little bit south of due east), and an elevation of 45 degrees which is about halfway between the horizon and the zenith.