We have performed philological analyses and source criticism on the section of astronomical observations in the astronomical treatise in Yeolryosilgisul. The section contains four paragraphs as follows. The first paragraph describes the establishment of the royal astronomical bureau, the construction of an observational station, and the recruits of astronomers. The second paragraph describes an episode where King Sejong regarded the earthquake and comet as portents from the Heaven and while he himself observed the comet as careful responses, he understood the efforts of the astronomers to appoint them as provincial governors of the provinces near to Seoul. The third paragraph states that King Sejong sent them to Ming China to get information on the calendar-making methods and astronomical instruments. The fourth paragraph describes a fact that astronomers were dispatched to the southern and northern ends of the territory to observe the star Canopus. However, our analyses demonstrate that these paragraphs do not agree with historical facts when being compared with authentic historical sources such as the Annals of the Joseon Dynasty. Hence, we conclude that it may be improper to adopt these statements as historical facts, so that we propose to verify previous historical descriptions made by adopting the statements.