Preheat Oven to 325º
Remove the turkey from the refrigerator at least 30 minutes before getting it ready to bake. Pat turkey dry with paper towels. Stuff the inside of the bird with the apples, onion, orange, celery and rosemary. Tie the legs together to hold the shape of the turkey. Season the inside with salt and pepper. Coat the entire bird with the softened butter.
Place the turkey in a large roasting pan. Cover the turkey for the first two hours with a buttered aluminum. Roast until a meat thermometer inserted between the body and the leg into the thickest part of the inner thigh (without touching the bone) registers 155°/160º. The juice should come out clear. Remove turkey from the oven and cover with aluminum foil. Wait 30 minutes before carving.
As a general rule, to covert conventional cooking to convection cooking, reduce the temperature by 25°F and the cooking time by approximately 10 to 15%.