- Amplitude is 24 degrees Northerly.
- Oblique Ascension, 20.
- Oblique Descension, 58.
- Ascensional Difference, 19.
- Semi-diurnal Arch, 109.
- His continuance above the horizon, 14½ hours.
- Sun rises at three quarters past four.
- Sun sets a quarter past seven.
These things for the Sun vary every day; but for a Fixed Star the day of the month need not be given, for they are the same all the year round.
- In the latitude of 51½ North,
- Syrus’s Amplitude is about 28 degrees Southerly.
- Oblique Ascension, 121.
- Oblique Descension, 75.
- Ascensional Difference, 23.
- Semi-diurnal Arch, 67.
- Continuance above the horizon, 9 hours.
Prob. XXXVIII. The Latitude and the Day of the Month being given; to find the Hour when any known Star will be upon the meridian, and also the time of its rising and setting.
Having rectified the globe for the latitude of the Sun’s place, bring the given Star to the meridian, and also to the East or West side of the horizon, and the index will shew accordingly when the Star culminates, or the time of the rising or setting.
Thus at London, on the 21st of January, Syrius will be upon the meridian, at a quarter past ten in the evening; rises at 5¼ hours, and sets at three quarters past two in the morning.
By the converse of this problem, knowing the time when any Star is upon the meridian, you may easily find the Sun’s place. Thus, bring the given Star to the meridian, and set the index to the given hour; then turn the globe ’till the index points to 12 at noon, and the meridian will cut the Sun’s place in the ecliptic. Thus when Syrius comes to the meridian at 10½ hours after noon, the Sun’s place will be ≈ ¼ deg.