The best lens for astro depends a lot on what kind of target is involved. I had a D5600 and now have a D780. I do a lot of wide field things (like MilkyWay) and found the Rokinon product line very good. I had a 10mm Rokinon for the D5600 and now have a 14mm one for the D780. I have been very happy with both.
I also have a Nikon 24mm f/2.8 lens as well, but tend to use the Rokinon more often. The 24mm seems to have more rings issues with astro things than the Rokinon.
I also have the 35mm f/1.8 lens I used with the D5600. I did mostly meteor shower things with it, but 35mm seemed too long for those.
Ed