Dry-brining — rubbing the turkey all over with a salt mixture and then letting it stand in the refrigerator for a day — is simpler than the wet method but is as effective in terms of imparting lots of flavor and ensuring moist meat. Allow 24 hours for dry-brining, then another two hours to bring the turkey to room temperature before roasting.
1. Dry-brine the turkey: One day before roasting, rinse turkey inside and out; pat dry with paper towels. Mix together 1/2 cup salt and the chopped thyme; season generously with pepper. Rub salt mixture on the following turkey parts in these amounts: cavity (2 tablespoons), legs (2 teaspoons each), wings (1 teaspoon each), breast halves (2 tablespoons each). Gently separate skin from breast. Rub remaining salt mixture under the skin on each side. Transfer to a deep pan, and cover, or to a large plastic bag set on a rimmed baking sheet (to catch juices). Refrigerate for 24 hours.
2. Drain accumulated juices from cavity, and pat inside of turkey dry with paper towels. Transfer to a large roasting pan fitted with a roasting rack, and place breast-side up. Bring to room temperature, 1 1/2 to 2 hours. Pat inside and outside of turkey dry with paper towels.
3. Roast the turkey: Preheat oven to 450 degrees, with rack in lowest position. Tuck wings under turkey. Stir chopped sage and thyme into butter, and rub over outside of turkey. Fill cavity with herb sprigs, bay leaves, apple cores, and onion; tie legs together with kitchen twine. Scatter apples and celery around rack. Place neck and giblets in pan. Add water to pan.
4. Roast turkey for 30 minutes. Baste with pan juices. Reduce oven temperature to 350 degrees; roast, basting every 30 minutes, for 1 1/2 hours more. Rotate pan, and add more water if pan is dry. Tent turkey with foil, and roast until a thermometer inserted into the thickest part of the thigh reaches 160 degrees, about 1 hour more. Let turkey stand for 30 minutes before transferring to a platter and carving. Reserve pan with contents if making gravy.