Astronomy Principles and Practice Fourth Edition.pdf

The Sun as a position finder 421
Figure 24.14. The variation of the solar corrected altitude with time well away from the meridian.
Observations taken on March 25th 2000: During the measurements, the altitude of the Sun ∼29 ◦
Refraction = 58 ′′ cot (alt)
= 58 ′′ (1·80)
= 1 ′ 40 ′′
Semi-diameter of Sun (from AA) = 16 ′ 02 ′′ .
Correction for obtaining true altitude of Sun’s centre = 16 ′ 02 ′′ − 1 ′ 40 ′′
= 14 ′ 42 ′′
Corrected Uncorrected Corrected
Corrected time Sextant reading Sextant reading altitude altitude
(UT) (R) (R + R + r)
10 h 00 m 31 s 57 ◦ 25 ′ 53 ′′ 57 ◦ 26 ′ 20 ′′ 28 ◦ 43 ′ 10 ′′ 28 ◦ 57 ′ 32 ′′
10 h 02 m 45 s 57 ◦ 50 ′ 39 ′′ 57 ◦ 51 ′ 06 ′′ 28 ◦ 55 ′ 33 ′′ 29 ◦ 09 ′ 55 ′′
10 h 04 m 41 s 58 ◦ 11 ′ 59 ′′ 58 ◦ 12 ′ 26 ′′ 29 ◦ 06 ′ 13 ′′ 29 ◦ 20 ′ 35 ′′
10 h 06 m 53 s 58 ◦ 35 ′ 57 ′′ 58 ◦ 36 ′ 24 ′′ 29 ◦ 18 ′ 12 ′′ 29 ◦ 32 ′ 34 ′′
10 h 09 m 02 s 58 ◦ 59 ′ 05 ′′ 58 ◦ 59 ′ 32 ′′ 29 ◦ 29 ′ 46 ′′ 29 ◦ 44 ′ 08 ′′
10 h 11 m 01 s 58 ◦ 20 ′ 21 ′′ 58 ◦ 20 ′ 48 ′′ 29 ◦ 40 ′ 24 ′′ 29 ◦ 54 ′ 46 ′′
Corrected Time (UT) Corrected Altitude
10 h 00·m52 28 ◦ 57·′53
10 h 02·m75 29 ◦ 09·′92
10 h 04·m68 29 ◦ 20·′58
10 h 06·m88 29 ◦ 32·′57
10 h 09·m03 29 ◦ 44·′13
10 h 11·m02 29 ◦ 54·′77
From the curve of the corrected altitude of the Sun against corrected time (see figure 24.14), a