The demarcation problem as one of the most prominent topics in the philosophy of science deserves a higher profile in science education literature as a part of the discussions about the instruction of the nature of science (NOS) concepts to generate a scientifically literate society. In this qualitative survey research study, the views of the practicing elementary, physics, and science teachers were investigated in regard to the demarcation of science from pseudoscience within the specific context of astronomy and astrology. The content analysis approach was employed in the study to analyze the open-ended responses of a total of 780 participant teachers. The teachers utilized the following six distinct dimensions in order to distinguish science from pseudoscience: universality, source, verification, methodology, aims, and progressiveness. The teacher responses about the demarcation of science from pseudoscience and non-science included the several elements of the logical positivism as a dominant philosophical framework. The conceptions of many teachers about science were not necessarily aligned with the contemporary representations of NOS in science education. In professional development programs, teachers should be allowed to refine their NOS conceptions by examining a pluralistic view of science reflecting the perspectives of multiple scholars from different disciplines.