Stonehenge and Other British Stone Monuments Astronomically Considered - Sir Norman Lockyer

Now it will at once be obvious that there must be a strict law connecting the position of a star with its place of rising or setting. Stars at the same distance from the celestial pole or equator will rise or set at the same point of the horizon, and if a star does not change its place in the heavens it will always rise or set in the same place.

The sun as it changes its position each day, in its swing N. and S. of the equator, will rise and set on any day in the same place as a star which permanently has the same distance from the equator as that temporarily occupied by the sun.

Here it will be convenient to introduce one or two technical terms: we generally define a star’s place by giving, as one ordinate, its distance in degrees from the equator: this distance is called its declination.

Further, we generally define points on the horizon by dividing its whole circumference into 360°, so that we can have azimuths up to 90° from the north and south points to the east and west points. We also have amplitudes from the east and west points towards the north and south points. We can say, then, that a star of a certain declination, or the sun when it occupies that declination, will rise or set at such an azimuth, or at such an amplitude. This will apply to both north and south declinations.

Then supposing the azimuth to be 39° in the N.E. quadrant, it is written N. 39° E. For the other quadrants we have N. 39° W., S. 39° E., and S. 39° W., respectively.

The following table gives the amplitudes of rising or setting (north or south) of celestial bodies having declinations from 0° to 64°, at Thebes and Stonehenge respectively.

Amplitudes at Thebes and Stonehenge.

Declina- tion.		Amplitude.
Declina- tion.		Thebes.				Stonehenge.
0	°	0	°	0	′	0	°	0	′
1		1		7		1		36
2		2		13		3		11
3		3		20		4		46
4		4		26		6		22
5		5		33		7		58
6		6		40		9		34
7		7		47		11		10
8		8		53		12		47
9		9		59		14		23
10		11		6		16		1
11		12		13		17		39
12		13		20		19		18
13		14		27		20		57
14		15		34		22		36
15		16		41		24		17
16		17		49		25		58
17		18		56		27		45
18		20		3		29		24
19		21		10		31		10
20		22		17		32		55
21		23		25		34		43
22		24		33		36		32
23		25		41		38		23
24		26		49		40		16
25		27		58		42		11
26		29		6		44		10
27		30		15		46		10
28		31		23		48		15
29		32		32		50		22
30		33		41		52		36
31		34		51		54		55
32		36		1		57		21
33		37		11		59		56
34		38		21		62		42
35		39		31		65		44
36		40		42		69		4
37		41		53		73		0
38		43		5		78		4
39		44		17		90		0
40		45		30
41		46		43
42		47		56
43		49		10
44		50		25
45		51		41
46		52		57
47		54		14
48		55		32
49		56		51
50		58		12
51		59		34
52		60		58
53		62		23
54		63		51
55		65		21
56		66		54
57		68		31
58		70		12
59		71		59
60		73		55
61		76		1
62		78		25
63		81		19
64	85	42

The amplitude is always the complement of the azimuth, so that amplitude + azimuth = 90°. Later on I shall give amplitudes for latitudes higher than that of Stonehenge, so that still more northerly monuments can be considered.