Ptolemy, scientist and mathmatician of the ancient world, wrote Almagest as a description of his learnings in his fields.
Included is mathematical formulas, Ptolemy’s models on the planets and their orbits, and other scientific learnings he made in his career. A backbone of scientific texts, it is still used today as a cornerstone of modern scientific learning. Ptolemy in his time discovered much of what grew to modern physics and astronomy.
Starting off, Springer Publishing has a book called A Survey of The Almagest which is one of their companion pieces in a long running series of companions to ancient texts. It does not include the actual text, instead quotes it and references those quotes with detail on context and meaning. It is a good addition to the text but unless you want to just understand the base meaning of Almagest this one isn’t for you. The Princeton University Press version is worthwhile as well. It offers a considerate translation that also took into account translations in other languages to guide it. It also has a good amount of extra bibliography for those interested in more works like it. Beyond that it doesn’t do a lot to stand out. It’s a good simple approach though. Oxford University Press has the best option to offer. Not only does it have a well informed translation it has plenty more of interest as well. Included are images, and diagrams to aid understanding. It also has a series of experiments and activities included for those interested in the real life use of the learnings detailed.