A cœlestiall planisphere: by J. Seller.

THE USE OF THE PLANISPHERE.

IN this Planisphere the Center re∣presents the North Pole of the World, about which are these four Concentrick Circles.

1. The Artick Circle being a lesser Circle distant from the Pole 23 deg. 30 min.

2. The Tropick of Cancer distant from the North Pole 66 degrees 30 minutes, and from the Equator 23 degrees 30 minutes.

3. The Equator, which is distant from the Pole 90 degrees, numbred 10, 20, 30, &c. to 360.

4. The Tropick of Capricorn, distant from the Equator Southward 23 de∣grees 30 minutes.

The Ecliptick makes an Angle of 23 degrees 30 minutes, with the E∣quator at the two opposite Points ♈ and ♎, and is divided into 12 Signs, marked ♈, ♉, ♊, &c.

Any Right Line supposed to be drawn from the Pole or Center of the Planisphere is a Meridian, but that which is called the Graduated Meri∣dian is numbred from the Equator both ways, with 10, 20, 30, &c.

By the help of this Planisphere, the following useful Problems may be re∣solved.

1. The Day of the Month being given to find the Sun's Place in the Ecliptick.

2. To find the Hour of the Night by any known Star, being upon the Meridian.

3, To know what Month and Day any Star will South at Mid∣night.

4. To find the Declination of any known Star.

5. To find the Right Ascension of any known Star.

6. To find the Time of the Moon's Southing any Day of her Age.

7. To find the Time of the Sun's Rising and Setting, any Day in the Year, in the Latitude of London.

For the Solution of those Seven Problems, you have Directions at the Corners of the Planisphere.

Prob. 8. Having the Sun's Place to find his Declination.

Extend your Compasses from the Center of the Planisphere, to the De∣gree of the Ecliptick that the Sun is in; then keeping one Point in the Center, turn the other to the Gra∣duated Meridian, and it will shew the Declination required.

Example. I desire to know the Sun's Declination when he is in 0 deg. 0 min. of Taurus.

Extend the Compasses from the Center to 0 deg. 0 min. of ♉ on the Ecliptick Circle, then turning them about as before directed, the move∣able Point falls on 11 deg. 30 min. which (because it is numbred from the Equator towards the North Pole) is North Declination, which was re∣quired.

Prob. 9. Having the Sun's Place given to find his Right Ascension.

Lay a Scale from the Center over that Point in the Ecliptick that the Sun is in, and observe where it cuts the Equator; the Degrees and Mi∣nutes so found, is the Right Ascension of the Sun at that time.

Example. The Sun's Right Ascension when he is in 0 deg. 0 min. of ♉, is required.

Lay your Scale from the Center of the Planisphere over 0 deg. 0 min. of ♉ in the Ecliptick, and it will cut in the Equator 27 deg. 54 min. the Sun's Right Ascension sought.

Having thus found the Right As∣cension of the Sun, and also the Right Ascension of any Star, by Prob. 5. you may find what time of the Day or Night the said Star will be upon the Meridian (besides the Method pro∣posed in Prob. 2.) Thus,

Subtract the Right Ascension of the Sun from the Right Ascension of the Star (borrowing 360 deg. if Sub∣traction cannot be made) the Re∣mainder reduce into Time (allowing for every 15 degrees one hour, and for every degree 4 minutes) it gives the hour and minute Afternoon that the Star will be upon the Meridian; and if it amount to more than 12 hours, subtract 12 hours from it, the Remainder is the hour and minute that the Star comes to the Meridian next Morning.

Example. It is required to know what time the Lyon's Heart will be upon the Meridian on the Day that the Sun's Place is found to be in 0 deg. 0 min. of vs.

The Right Ascension of the Lyons Heart, is found (by Prob. 5.) to be 147 degrees 48 minutes, from which subtract the Right Ascension of the Sun (which is found by Prob. 9. to be) 270 degrees; the remainder 237 deg. 48 min. reduced to Time gives 15 hours 51 minutes Afternoon, from which abating 12 hours, the Re∣mainder 3 hours 51 minutes is the hour of the Lyons Heart coming to the Meridian in the Morning.

Note, If you put a small Bead upon the String that is fixed at the Center of the Planisphere, the String and Bead so fitted will supply the Use of Scale and Compasses, the String ser∣ving instead of a Scale, and the Bead slipping up and down upon the String at pleasure, gives any Extent from the Center upon the Graduated Me∣ridian.

[illustration] celestial planisphere

A COELESTIALL PLANISPHERE By J. Seller.

The Use of this Coelestiall Planisphere Ilustrated for want of roome by the Examples only.

Prob: 1. The day of the Month being given to find y^e Suns place.

Example Let the day be the 5^th. day of May, on which day the Suns place is required, lay a thrid or Ruler from the Center, to y^e Circle of Months to y^e 5^th. of May. And it will shew you in the Circle of Signes that the Sun is 25^d. 20 in Taurus, & on the fifth day of November, the Sun is in 24. deg: of Scorpio, And on the 5^th. of Ianuary y^u. will find the Sun to be in the 26. of Capricorn. And on the Twentith day of February you will find the Suns place to be in the 13^th. deg: of Pisses.

Problem 2. To find the Hour of the Night by any Star upon the Meridian.

Example on y^e 30. of Ianuary. I see y^e Bulls eye upon the South part of y^e Meridian. I requier to find y^e hour of the Night. Lay y^e thrid or edg of a Ruler from y^e Center upon y^e Buls eye. And note where it cutts y^e Hour Circle, from which point sett one point of your Compasses, and extend y^e other point to the Hour of 12. y^e same Extent. y^e same way will reach from y^e 30^th. of Ianuary to 50. min. past Six of the Clock.

Problem 3. To know what time of the yeare y^e Buls eye will be upon the Meridian at 12 of the clock at night. Lay a Ruler over the diameter of y^e Planispher & through y^e center of y^e Buls eye, then y^e oposite part of y^e Ruler will cut y^e 16 day of Novemb: the night on which the Buls eye wil be upon the Meridian.

Prob. 4. To find y^e Declination of any Star.

Example Extend your Compasses from the Center of the Planisphere to the Buls eye, then turne the foot of your Com∣passes to the graduated Meridian, and there it will shew you the Declination from the Equinoctiall to be 15. deg: 48. min.

Problem 5^th. To find the Right Ascention of any Star.

Example of the Buls eye. Lay a thrid or edge of a Ruler from the center of the Planisphere over the Bulls eye, and you will find that it cutts in the circle of Signes 64^d. 27′. counting it from Aries.

Example of the Lyons hart, Lay a thrid or Ruler over the Center of the Planisphere, & over the Lyons hart, you will find that the thrid or Ruler will cutt in the circle of Sines in 27 deg: 48. of Leo. which being counted from the first Point of Aries is 247. deg: 48. minutes which is the Right Assention of the Lyons hart.

Prob 6 To find y^e Moons So∣uthing any day of her Age And y^e time of full Sea

Example I Requi∣er y^e time of y^e Moons Southing when she is 6 dayes old. seek her Age amongst y^e small figures y^t are plast among the Hours, & y^u will find y^e figure 6 stand at 4. a clock 53′. the time of the Moons Southing. To which if you a•• y^e time of Flowing, it will give y^e time of high water in any place, for Londō add 3. which makes 7. of the clock and 53′. past y^e time of High water at London bridge.

Prob. 7 To find the Rising and Setting of the Sun every day in the yeare.

Example I Require to know y^e Rising and setting of the Sun on y^e 26 day of December. Therefore lay a thrid or the edg of a Ruler from the Center over the day of the Month, then in the outer Circle it will shew you that the Sun riseth at 8 of the clock 9 minuts past And Setteth at foure of the Clock 9 minuts wanting