CHAP. 11. How to find the Oblique Ascension or Descension of any point in the Ecliptique.
OBlique ascension is when a less arch or portion of the Aequator ••iseth, then doth of the Zodiack, or else of that Star may be said to rise obliquely with whom a less portion of the Aequator as∣cendeth above the Horizon, & so the oblike Descension or setting of a Star, is when a less proportion of the Aequator descendeth with it, then doth in a right Sphere.
In the former Diagram, D C represents the right Ascension, M C the Ascensional Difference, D M the oblique Ascension, D B an arch of the Ecliptique above the Horizon, which being greater then D M, a Star in this position of the Sphere, is said to rise obliquely. The quantity whereof is found, by deducting the Ascensional difference C M from the right as∣cension D C, according to the direction following.
If the Declination be
- North
- Subt. The Ascensional Difference from the right Ascension, and it giveth the oblique Ascension.
- Adde The Ascensional Difference to the Right Ascension, and it giveth the oblique Descension.
- South
- Adde The Ascensional Difference to the Right Ascension, and it giveth the oblique Ascension.
- Subt. The Ascensional Difference from the Right Ascensi∣on, it giveth the oblique Descension.