Juice 5 oranges over a sieve, making about 1 1/2 cups juice. Zest 1 orange; set zest aside. Using a paring knife, remove the skin, pith, and outer membrane from the zested orange. Carefully cut each segment away from white membranes. This is called supreming the orange. Set segments aside.
Place asparagus in a large saute pan. Add 1/2-inch of water, and bring to a boil. Lower the heat, and steam, about 8 minutes. Just before asparagus are fully cooked, drain liquid from the saute pan. Add 1/4 cup orange juice, and simmer until asparagus are fork-tender. Remove from heat. Season with salt and pepper. Cover, to continue steaming while finishing the sauce.
Meanwhile, in a small saucepan, bring remaining 1 1/4 cups orange juice to a boil. Add vinegar, lower heat, and simmer until juice is reduced to 1/3 cup. Remove from heat, and stir in butter, 1 piece at a time, until sauce is thick and creamy. Season with salt and pepper. Transfer asparagus to a warm platter, drizzle with sauce, and garnish with reserved orange segments, reserved zest, and tarragon.
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