386. From the Sum of the Semi-diameters of the Moon and Earth’s Shadow, subtract the Moon’s Latitude; the remainder is the parts deficient. Then, as the Semi-diameter of the Moon is to 6 Digits, so are the parts deficient to the Digits eclipsed.
387. If the parts deficient be more than the Moon’s Diameter, the Eclipse will be total with continuance; if less, it will not be total; if equal, it will be total, but without continuance.
388. Now collect the Elements for projecting this Eclipse.
| ʹ | ʺ | |
|---|---|---|
| Moon’s horizontal Parallax | 55 | 32 |
| Sun’s horizontal Parallax (always) | 10 | |
| The Sum of both Parallaxes | 55 | 42 |
| From which subtract the Sun’s Semi-diameter | 15 | 54 |
| Remains the Semi-diameter of the Earth’s Shadow | 39 | 48 |
| Semidiameter of the Moon | 15 | 2 |
| Sum of the two last | 54 | 50 |
| Moon’s Latitude subtract | 9 | 56 |
| Remains the parts deficient | 45 | 0 |
| Moon’s horary motion | 30 | 46 |
| Sun’s horary motion subtract | 2 | 24 |
| Remains the Moon’s horary motion from the Sun | 28 | 22 |
To project a lunar Eclipse.
Fig. III.
389. This done, make a Scale of any convenient length as W, whereof each division is a minute of a degree; and take from it in your Compasses 54 Minutes 50 Seconds, the Sum of Semi-diameters of the Moon and Earth’s shadow; and with that extent as a Radius, describe that Circle OVLG round C as a Center.
From the same Scale take 39 Minutes 48 Seconds, the Semi-diameter of the Earth’s shadow, and therewith as a Radius, describe the Circle UUUU for the Earth’s shadow, round C as a Center. Subtract the Moon’s Semi-diameter from the Semi-diameter of the Shadow, and with the difference 24 Minutes 46 seconds as a Radius, taken from the Scale W, describe the Circle YZ round the Center C.
Draw the right line AB through the Center C for the Ecliptic, and cross it at right Angles with the line EG for the Axis of the Ecliptic.
Because the Moon’s Latitude in this Eclipse is North Descending, § [384], set off the Angle of her visible Path with the Ecliptic 5 Degrees 38 Minutes (Page [202].) from E to V; and draw VCv for the Axis of the Moon’s Orbit. Had the Moon’s Latitude been North Ascending, this Angle must have been set off from E to f. N. B. When the Moon’s Latitude is South Ascending, the Axis of her Orbit lies the same way as when she has North Ascending Latitude; and when her Latitude is North Descending, the Axis of her Orbit lies the same way as when her Latitude is South Descending.
Take the Moon’s true Latitude 9ʹ 56ʺ in your Compasses from the Scale W, and set it off from C to F on the Axis of the Ecliptic because the Moon is north of the Ecliptic; (had she been to the South of it, her Latitude must have been set off the contrary way, as from C towards v:) and through F, at right Angles to the Axis of the Moon’s Orbit VCv, draw the right line LMHNO for the Moon’s Orbit, or her Path through the Earth’s shadow. N. B. When the Moon’s Latitude is North Ascending, or North Descending, she is above the Ecliptic: but when her Latitude is South Ascending, or South Descending, she is below it.