c# - Problems while moving picturebox on ellipse -

i want make program simulate planets moving in solar system planet going out of orbit.

picture 1

picture 2

here try move planets around sun.

planetday number of days on planet reported day of earth

the planets not following orbit , think here problem i'm not sure, when modify location of planet convert x , y int , when round numbers

private void moveplanets() {         double x;         double y;          int k = 0;          foreach (picturebox pic in picturebox1.controls)         {             if (pic.name == "sun")             {                 continue;             }              x = sun.location.x + (rectangle[k].width / 2 * math.cos(planetday[k] + alpha));             y = sun.location.y + (rectangle[k].height / 2 * math.sin(planetday[k] + alpha));             pic.location = new point(convert.toint32(x), convert.toint32(y));             k++;              if (k == 8)             {                 k = 0;             }         }          alpha += 0.1; } 

here generate rectangle use draw ellipses

private void orbit() {               int x1 = 30;          foreach (picturebox pic in picturebox1.controls)         {             if (pic.name == "sun")             {                 continue;             }              rectangle r = new rectangle                (                    pic.location.x + pic.size.width / 2,                    (sun.location.y + sun.size.width / 2) - x1,                    ((sun.location.x + sun.size.width / 2) - (pic.location.x + pic.size.width / 2)) * 2,                    x1 * 2                );             rectangle.add(r);             x1 += 36;          } } 

and here draw ellipses

private void picturebox1_paint(object sender, painteventargs e) {         pen p = new pen(color.white, 1f);          foreach (rectangle rec in rectangle)         {             e.graphics.drawellipse(p, rec);         } } 

can me problem ?