It is remarkable that the work of Hipparchus is so valued by modern astronomers that the modern values of stellar magnitude (aka how bright they appear in the sky) was scaled to match the values given by Hipparchus in his original star charts. There are obviously some adjustments and Hipparchus didn't get all of the stars perfectly, but at the same time if the apparent stellar magnitude seems to have been off by a substantial amount the presumption is that something has happened to the star in the last few centuries rather than suspecting the ancient values were wrong.

In other words, real science can even be gleaned from these ancient manuscripts that result in modern discoveries of new astronomical phenomena too. It really is that good in some cases not to mention that some ancient astronomers were extremely meticulous with their data collection that it still has some modern relevance.