Some authorities believe that the Gemara is not talking about solar eclipses. Rav Yonasan Eybeschutz (Ye’aros Devash 2:10) suggests that the Gemara is referring to sunspots. While solar eclipses can be predicted, sunspots cannot and are caused by sin. Rav Yehosef Schwartz (Divrei Yosef 1:9) suggests that the Gemara is discussing unexpected atmospheric phenomena. He says that on 28 Iyar 1838 in Jerusalem at 4pm, the sun turned dark red for about an hour. Everyone was amazed by the sight. Over the next three months, Jerusalem experienced a terrible plague with many deaths. Rav Schwartz says that this was an example of the Talmudic phenomenon. - TorahMusings.com