Guthke, K. S. Are we alone?: The idea of extraterrestrial intelligence in philosophy and literature from Copernicus to H.G. Wells / Karl S. Guthke. Utopian vision, technological innovation and poetic imagination.(1990).
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Guthke, Karl S. "Are We Alone?: The Idea of Extraterrestrial Intelligence in Philosophy and Literature from Copernicus to H.G. Wells / Karl S. Guthke." Utopian Vision, Technological Innovation and Poetic Imagination.(1990) .
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Guthke, Karl S. "Are We Alone?: The Idea of Extraterrestrial Intelligence in Philosophy and Literature from Copernicus to H.G. Wells / Karl S. Guthke." Utopian Vision, Technological Innovation and Poetic Imagination.(1990), .
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.