I'm not the intended audience for this thing since I'm not an astrologer at all, but I appreciate that the ask is straightforward and concrete - I can see that the thing you are trying to make could potentially be well received by it's target audience, even if that audience is not me!
That may be an assumption worth validating, actually - a way to make this pitch more compelling to outsiders would be some evidence that you have or are planning to do "market research" of your target audience to demonstrate that there are other astrological researchers who would be interested in subscribing to such a publication.
But I can see that this is clearly a passion project for you with a concrete output that is of learning value (potentially not even just to astrologers, since astronomical maths and science is such a fascinating topic) so I think this is the starting point for something concrete with real value to some people.