Evolve / Evolve To...   ()

Summary

Evolves the frontmost simulation forward or backward to a specified date/time, or evolves to the next or previous event of a particular type.

Description

When you select this command, an input dialog will be displayed allowing you to specify the date/time that you wish the frontmost simulation to evolve to. If you fill this in and accept the input dialog, AstroGrav will evolve the simulation forward or backward to the specified date/time or until you stop the evolution.

Alternatively, the input dialog allows you to specify the next or previous event of a particular type. If you fill in the appropriate fields and accept the input dialog, AstroGrav will evolve the simulation forward or backward until the specified event is reached or until you stop the evolution. The following types of event are available.

• The next or previous pericenter of any object. A pericenter is when the object is closest to its parent.
• The next or previous apocenter of any object. An apocenter is when the object is farthest from its parent.
• The next or previous ascending node of any object. An ascending node is when the z-component of the object switches from being less than to being greater than the z-component of its parent.
• The next or previous descending node of any object. A descending node is when the z-component of the object switches from being greater than to being less than the z-component of its parent.

• The next or previous opposition of any two objects as seen from a third object. An opposition is when the third object and the projections of the other two objects onto the plane of the third object's orbit all lie in a straight line, with the third object in the middle.
• The next or previous conjunction of any two objects as seen from a third object. A conjunction is when the third object and the projections of the other two objects onto the plane of the third object's orbit all lie in a straight line, with the third object at one end.
• The next or previous quadrature of any two objects as seen from a third object. A quadrature is when the angle between the two objects as seen from the third object is 90 degrees.

• The next or previous transit of any two objects as seen from a third object. A transit is when the two objects appear to overlap as seen from the third object, with the nearer object appearing the smaller.
• The next or previous occultation of any two objects as seen from a third object. An occultation is when the two objects appear to overlap as seen from the third object, with the nearer object appearing the larger.
• The next or previous overlap of any two objects as seen from a third object. An overlap is either a transit or an occultation.

• The next or previous minimum distance between any two objects. A limiting distance can be specified if desired to eliminate unwanted minimums.
• The next or previous maximum distance between any two objects. A limiting distance can be specified if desired to eliminate unwanted maximums.
• The next or previous minimum angle between any two objects as seen from a third object. A limiting angle can be specified if desired to eliminate unwanted minimums.
• The next or previous maximum angle between any two objects as seen from a third object. A limiting angle can be specified if desired to eliminate unwanted maximums.

• The next or previous collision between any two objects.

When evolving to an event, an automatically calculated time step is used, regardless of the setting that is displayed with the Evolve / Settings... command. Also, collision detection is temporarily switched off while evolving to an event. If you request an event (such as the next collision of Jupiter and Saturn) that never occurs, AstroGrav will evolve indefinitely searching for the event until you stop the evolution.

An Animate checkbox allows you to choose whether or not to display the state of the simulation after each time step. If evolution is animated, you can watch the simulation evolve as when you use the Evolve / Run Backward and Evolve / Run Forward commands. While AstroGrav is calculating the next state of the system, the Evolve / Stop command is available for you stop the evolution, and the Evolve / Settings... command is available for you to change the time step. If evolution isn't animated, a progress bar is displayed if evolution is going to take more than a couple of seconds, and a Cancel button is available to stop evolution if desired. Non-animated evolution is usually much faster than animated evolution, so you should only use animated evolution if you want to watch what's happening.

There is also a Beep when finished checkbox that can be useful if you're doing a very long evolution and want an audible alert when it's finished.

The time that it takes AstroGrav to evolve the system through one time step is extremely variable, but depends mainly on the following factors.

• The fewer objects there are in a simulation, the less time it will take to evolve. If there are only a few objects in a simulation, it may evolve through one time step in a tiny fraction of a second, whereas if there are thousands of objects in a simulation, it may take many seconds to evolve through one time step.

• The greater the proportion of objects whose mass is below the mass threshold (specified with the Evolve / Settings... command), the less time it will take to evolve. If a simulation has a significant proportion of objects that have low masses, increasing the mass threshold may significantly reduce the time it takes to evolve, without significantly reducing the accuracy.

• The shorter the time step is, the less time it will take to evolve. Reducing the time step can significantly reduce the time it takes to evolve, but this is not always the case - if the time step is already small, reducing it will have little effect on the evolution time.

• The faster your computer is, the less time it will take to evolve.

See Also:

• Evolve / Run Backward()that evolves the frontmost simulation backward one time step after another until it is stopped.

• Evolve / Run Forward()that evolves the frontmost simulation forward one time step after another until it is stopped.

• Evolve / Settings...()that sets the evolver settings of the frontmost simulation.

• Evolve / Stop()that stops the evolution of the frontmost simulation.

• Edit / Date/Time...()that edits the current date/time of the frontmost simulation.

• Edit / Undo()that undoes the latest change to the frontmost simulation.

• Edit / Redo()that redoes the most recently undone change to the frontmost simulation.

• Tools / Create Movie...()that creates a movie of the frontmost simulation while it is evolving.

• Window / New Ephemeris...()that generates an ephemeris for each selected object in the frontmost simulation, while it is evolving.

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