PUSH AND POP OF MODELVIEW MATRIX



   glPushMatrix();                 /* save start matrix */

   glPushMatrix();                 /* save start matrix again */

   glRotatef ((GLfloat) year, 0.0, 1.0, -1.0);  /* rotate sun */
   glutWireSphere(1.0, 20, 16);    /* draw sun */

   glPopMatrix();                  /* get start matrix, forget about sun */

   glRotatef ((GLfloat) year, -1.0, 2.0, 0.0);  /* rotate planet+moon */
   glTranslatef (2.0, 1.0, 0.0);   /* translate from sun center */

   glPushMatrix();                 /* save position of planet+moon */

   glRotatef ((GLfloat) day, -0.3, 1.0, 0.0);   /* rotate planet */
   glutWireSphere(0.2, 10, 10);    /* draw planet */

   glPopMatrix();                 /* get position of planet+moon */

   glRotatef ((GLfloat) day, 0.0, 0.0, 1.0);  /* rotate moon itself */
   glTranslatef (0.0, 1.0, 0.0);   /* translate from planet center */
   glRotatef ((GLfloat) day*3, 0.0, 0.0, 1.0);  /* rotate around planet */
   glutWireSphere(0.1, 10, 10);    /* draw moon */

   glPopMatrix();                  /* get start matrix, forget previous */