# Quick question

**URL:** <https://forum.kirupa.com/t/quick-question/240399>\
**Category:** Uncategorized\
**Created:** [October 2, 2007, 5:27pm UTC](https://forum.kirupa.com/t/quick-question/240399 "2007-10-02T17:27:18Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![br\_provi\_707](https://avatars.discourse-cdn.com/v4/letter/b/b3f665/32.png) [@br\_provi\_707](https://forum.kirupa.com/u/br_provi_707)\
**Post date:** [October 2, 2007, 5:27pm UTC](https://forum.kirupa.com/t/quick-question/240399/1 "2007-10-02T17:27:18Z")

</div>

Hi

So I’m making a simple astronomy animation where mars is orbiting and leaving a trail behind it. When mars comes full circle, I want the trail to be erased and start over.

I have two questions:  
What condition can I use to test to see if its the right time to restart the trail (the if \_y\<200 is just there for testing)  
and  
How can I restart the trail? Currently when I call makeTrail() a second time nothing happens.

```auto

var marsStart:Number = 0;
var marsSpeed:Number = 6;
var marsDistance:Number = 70 ; // Distance from mars to point it rotates around (orbit); radius of rotation.

// Set up the mars trail.
function makeTrail() {
    
_root.createEmptyMovieClip("marsTrail",2);
marsTrail.lineStyle(0,0x999999,50);
marsTrail.moveTo(mars._x,mars._y)
}

//create mars trail for the first time
makeTrail();

//create marstrail during animation
mars.onEnterFrame = function() {
    this._x = orbit._x + Math.cos(marsStart/180*Math.PI)*marsDistance;
    this._y = orbit._y + Math.sin(marsStart/180*Math.PI)*marsDistance;
    marsStart += marsSpeed;
    marsTrail.lineTo(mars._x,mars._y);
    
    //Erase the mars trail 
    if (this._y < 200) {
        marsTrail = null;
        makeTrail();
}
// else{
// marsTrail._alpha = 50;
// }
}

var orbitStart:Number = 0;
var orbitSpeed:Number = 1;
var orbitDistance:Number = 150; // Distance form earth to center of mars orbit.

// Set up the orbit trail (the ring).
_root.createEmptyMovieClip("orbitTrail",3);
orbitTrail.lineStyle(0,0xdddddd,100);
orbitTrail.moveTo(orbit._x,orbit._y);

orbit.onEnterFrame = function() {
    this._x = earth._x + Math.cos(orbitStart/180*Math.PI)*orbitDistance;
    this._y = earth._y + Math.sin(orbitStart/180*Math.PI)*orbitDistance;
    orbitStart += orbitSpeed;
    orbitTrail.lineTo(orbit._x,orbit._y);
}

//Move the mars orbit path
morbitpath.onEnterFrame = function () {
    this._x = orbit._x;
    this._y = orbit._y;
    
}

```

Thanks. This is the first actionscript I’ve ever done and I need all the help I can get.

ps there are already movieclips on the stage called mars, morbitpath, earth, orbit