AstroGrav Help / Tutorial / Exercise 3 - Using Model Windows

Exercise 3 - Using Model Windows

This exercise teaches you how to use model windows, and should take about 20 minutes to complete.

Opening the Sample Simulation

If you already have the Tutorial sample simulation open, choose the File / Revert to Saved menu item, which will return the simulation to the same state that it was in when you first opened it. Otherwise, go through the following steps to open it.

If you don't already have AstroGrav running, double-click on the AstroGrav application icon () to start it running.
When the Open Simulation file chooser dialog is displayed, navigate to and open the Sample Simulations folder.
Select and open the Tutorial.ast file in the English folder.

The Tutorial sample simulation will then open, and you will see the simulation's three windows displayed on your screen.

The Tutorial: Model window should be the frontmost window, but if it isn't, click on it to bring it to the front. This window is a three-dimensional interactive model in which you will see the Sun and the five innermost planets - Mercury, Venus, Earth, Mars, and Jupiter. This exercise will show you how to manipulate this three-dimensional interactive model and navigate around it.

Navigating With the Mouse

Go through the following steps to learn how to navigate around model windows.

Drag the mouse pointer around the window, without holding down any of the modifier keys, and watch how the view changes to allow you to look in different directions. Your viewpoint remains the same while you look in different directions, as if you were turning your head while remaining in the same position.
Now, hold down the Alt key, and drag the mouse pointer around the window, and watch how the view rotates clockwise and anticlockwise. Your viewpoint remains the same while your view rotates. so that you can view the system on its side or upside down.
Now, hold down the Shift key, and drag the mouse pointer around the window, and watch how the solar system rotates about the Sun, so that you can see it from different directions.
Now, hold down the Control key (Command key on a Mac), and drag the mouse pointer around the window, and watch how your viewpoint moves towards and away from the Sun. Dragging the mouse pointer towards the Sun moves you towards the Sun, and dragging the mouse pointer away from the Sun moves you away from the Sun.

Combining the Four Different Mouse Dragging Operations

You have now learnt the following four different mouse dragging operations.

Looking around, by dragging the mouse pointer.
Rotating the view, by dragging the mouse pointer while holding down the Alt key.
Rotating the system, by dragging the mouse pointer while holding down the Shift key.
Moving to/from, by dragging the mouse pointer while holding down the Control key (Command key on a Mac).

Spend a minute or two experimenting with these different operations, until you feel confident that you can use them to obtain any view that you want. Notice how rotating the system is a very good way to obtain a three-dimensional impression of the system.

Selecting an Object

In order to view or edit the details of an object (covered in a later exercise of this tutorial), it is necessary to first select the required object. Go through the following steps to learn how to select and deselect objects, and view some of the information about the selected object.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Now, click on the Earth without holding down any of the modifier keys, and check that the Earth's orbit has been highlighted. If it hasn't, your click was probably not close enough to Earth, so try again until the Earth's orbit highlights.
Have a look at the information that is displayed in the top-left corner of the window. You will see that the Earth is the currently selected object, and that its distance, magnitude, and phase are displayed.
Now, click on Venus without holding down any of the modifier keys, check that its orbit highlights, and see how the information that is displayed in the top-left corner of the window now refers to Venus.
Now, click on the Sun without holding down any of the modifier keys, and see how the information that is displayed in the top-left corner of the window now refers to the Sun. There is now no orbit highlighted because the Sun is the central object in the system, and the "phase" information is now missing because phases only apply to non-luminous objects (such as planets) and not to luminous objects (such as stars).
Now, click anywhere in the window where there are no objects present, and see how the information that is displayed in the top-left corner of the window is now cleared, showing that there is now no object selected.

Fixing an Object

When rotating the system, moving towards or away from the Sun, and evolving the simulation, you have probably noticed that the Sun remains fixed in position while everything else moves. This is indicated in the top-left corner of the window by the "Fixed: Sun" entry. Go through the following steps to learn how to change the object that is fixed in position while performing these operations.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Click on the Earth while holding down the Shift key, and check that in the top-left corner of the window, the Earth has now replaced the Sun as the fixed object.
Now, hold down the Shift key, and drag the mouse pointer around the window, and notice how the Earth now remains fixed in position while everything else rotates about it.
Now, hold down the Control key (Command key on a Mac), and drag the mouse pointer around the window, and notice how your viewpoint now moves towards and away from the Earth instead of toward and away from the Sun.
Choose the Evolve / Run Forward menu item (or the tool), which will start the simulation running forward in time. Notice how the Earth now remains fixed in position while everything else moves.
Finally, stop the simulation running by using the Evolve / Stop menu item (or the tool).

You can also clear the fixed object by clicking anywhere in the window where there are no objects present while holding down the Shift key. When you do this, the center of mass becomes the fixed point, instead of one of the objects. In the case of the Tutorial sample simulation, it is difficult to tell the difference between clearing the fixed object and having the Sun as the fixed object, because the center of mass of the Solar System is so close to the center of the Sun.

Next, go through the following steps to see a more practical use for what you have just learned.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Click on Jupiter while holding down the Shift key, and check that in the top-left corner of the window, Jupiter has now replaced the Sun as the fixed object.
Now, drag the mouse pointer around the window, without holding down any of the modifier keys, until Jupiter is near the center of the window.
Now, hold down the Control key (Command key on a Mac), and repeatedly drag the mouse pointer towards Jupiter, watching how your viewpoint moves towards Jupiter until its four moons become visible, and the largest of their orbits eventually almost fills the window.
Choose the Evolve / Run Forward menu item (or the tool), which will start the simulation running forward in time.
Now, choose the Evolve / Settings... menu item (or the tool), which will result in the Evolve Settings input dialog being displayed.
Change the time step from 1.0 day to 1.0 hour and accept the dialog. Notice how the simulation now runs at a more acceptable speed for viewing the motion of Jupiter's moons.
Experiment with rotating the system, by dragging the mouse pointer with the Shift key, and notice how your view (including the phase of Jupiter) changes. See if you can change the phase of Jupiter to zero, so that the Sun is 'hidden' behind Jupiter.
Finally, stop the simulation running by using the Evolve / Stop menu item (or the tool).

Viewing From an Object

Go through the following steps to learn how to view from a particular object.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Click on Jupiter while holding down the Control key (Command key on a Mac), and notice how your viewpoint jumps to Jupiter, with "Viewpoint: Jupiter" now being displayed in the top-left corner of the window.
Now, hold down the Shift key, and drag the mouse pointer around the window, and notice how a dialog appears telling you that rotating the system is impossible while viewing from an object. Cancel this dialog.
Now, hold down the Control key (Command key on a Mac), and drag the mouse pointer around the window, and notice how a dialog appears telling you that moving to/from is impossible while viewing from an object. Cancel this dialog.
Now, drag the mouse pointer around the window, without holding down any of the modifier keys, and watch how the view changes to allow you to look in different directions. Unlike rotating the system and moving to/from, looking around and rotating the view are allowed while viewing from an object because these operations do not move the viewpoint. Position the view so that the Sun is somewhere near the center of the window.
Choose the Evolve / Run Forward menu item (or the tool), which will start the simulation running forward in time.
Now, choose the Evolve / Settings... menu item (or the tool), which will result in the Evolve Settings input dialog being displayed.
Change the time step from 1.0 day to 1.0 hour and accept the dialog. Notice how the simulation now runs at a more acceptable speed for viewing the motion of Jupiter's moons.
Finally, stop the simulation running by using the Evolve / Stop menu item (or the tool).

You can also detach your viewpoint from the object that you are viewing from by clicking anywhere in the window where there are no objects present while holding down the Control key (Command key on a Mac). When you do this, you can then rotate the system about the fixed object and move to/from the fixed object as desired.

Displaying the Model Navigation Guide

You will probably have trouble remembering all the mouse click and mouse drag commands, so a model navigation guide is provided to remind you. Go through the following steps to learn how to use the model navigation guide.

Choose the Help / Model Navigation menu item, and notice how the Model Navigation Guide window is displayed.
Study the information provided until you understand it, so that you will be able to quickly use the model navigation guide in the future.
Finally, close the Model Navigation Guide window when you have finished studying it.

Changing the Magnification

Go through the following steps to learn how to change the magnification of a model window.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Check that the field of view displayed in the top-right corner of the window is very roughly 40°x30°
Now, choose the View / Magnification / Much Larger menu item (or the tool), and notice how the magnification is greatly increased, with a corresponding decrease in the field of view displayed in the top-right corner of the window.
Now, choose the View / Magnification / Much Smaller menu item (or the tool), and notice how the magnification is greatly decreased, with a corresponding increase in the field of view displayed in the top-right corner of the window.
Repeatedly choose the View / Magnification / Larger menu item (or the tool), and notice how each time the magnification is slightly increased, with a corresponding decrease in the field of view displayed in the top-right corner of the window.
Repeatedly choose the View / Magnification / Smaller menu item (or the tool), and notice how each time the magnification is slightly decreased, with a corresponding increase in the field of view displayed in the top-right corner of the window.

Increasing the magnification seems to have a similar effect to moving your viewpoint towards the fixed object, but they are in fact very different, because when changing the magnification your viewpoint remains fixed. In particular, if you want a clearer view of whatever you're looking at while viewing from an object, you can increase the magnification, whereas moving your viewpoint is not possible.

Changing the Brightness

Go through the following steps to learn how to change the brightness of a model window.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Look at the orbits beyond Jupiter's, and notice that Saturn's orbit (the innermost) is clearly visible, Uranus' orbit (the next innermost) is dimly visible, and Neptune's and Pluto's orbits are not visible at all. This is because at the current brightness settings Uranus is only just bright enough to be visible, and Neptune and Pluto are not bright enough to be seen at all.
Now, choose the View / Brightness / Much Brighter menu item (or the tool), and notice how the brightness is greatly increased, with Uranus' orbit now clearly visible and Neptune's orbit now dimly visible.
Now, twice choose the View / Brightness / Much Dimmer menu item (or the tool), and notice how each time the brightness is greatly decreased, with Mars' orbit now only dimly visible and Uranus's orbit now no longer visible at all.
Repeatedly choose the View / Brightness / Brighter menu item (or the tool), and notice how each time the brightness is slightly increased.
Repeatedly choose the View / Brightness / Dimmer menu item (or the tool), and notice how each time the brightness is slightly decreased.

Changing the Show Options

There are several "on-off" switches that you can use to change how a model window is displayed. Go through the following steps to learn how to switch them on and off, and to learn what effect they have.

Choose the File / Revert to Saved menu item, which will return the sample simulation to the same state that it was in when you first opened it.
Now, choose the View / Show / Auras menu item (or the tool), and notice how the objects are now displayed as simple circles, instead of with auras. Displaying the objects as simple circles does not look as good as displaying them with auras, and the simple circles usually exaggerate the apparent sizes of the objects, but refreshing model windows may be significantly faster on some computers when the objects are displayed as simple circles. Choose the same command again to return the display to its original state.
Now, choose the View / Show / Names menu item (or the tool), and notice how the names of the objects are now hidden. Choose the same command again to return the display to its original state.
Now, choose the View / Show / Velocities menu item (or the tool), and notice how the velocities of the objects are now shown as vectors leading from the objects and pointing in the direction of motion. Choose the same command again to return the display to its original state.
Now, choose the View / Show / Accelerations menu item (or the tool), and notice how the accelerations of the objects are now shown as vectors leading from the objects and pointing in the direction of acceleration. Choose the same command again to return the display to its original state.
Now, choose the View / Show / Orbits menu item (or the tool), and notice how the orbits of the objects are now hidden. Choose the same command again to return the display to its original state.
Now, choose the View / Show / Invisibles menu item (or the tool), and notice how the outer orbits have become clearly visible, and the appearance of Jupiter has changed. This command makes any objects that are too faint to see properly at the current brightness setting display as an 'x', with their names and orbits clearly visible. It is an alternative to changing the brightness setting when you are interested in objects that are too faint to see properly at the current brightness setting. Choose the same command again to return the display to its original state.
Now, choose the View / Show / Axes menu item (or the tool), and notice how the coordinate axes are now visible. Choose the same command again to return the display to its original state.
Experiment with various combinations of these "on-off" switches to see the various effects that you can create.

Next: Using Other Types of Windows

You've now completed Exercise 3, and are ready to move on to Exercise 4, which teaches you how to use other types of windows.

Exercises | Previous | Next