Oldalképek
PDF
ePub

200. Tables for converting mean solar Time into Degrees and

Parts of the terrestrial EQUATOR; and also for converting De. grees and Parts of the EQUATor into mean solar Time.

TABLE I. For convertinchi ABLE il. For converting
Time into Degrees and Degrees and Parts of the
Parts of the Equator.

Equa'or into Time,

Hours
Degrees

Hours
Minutes

Min.
Min.

Deg:
Min. Sec.

Sec.
Deg. 1 Min. 1 Sec.

Sec.
Min. | Sec. | Thirds
Hours | Min. | Sec. 1

Min. 1 Sec. | Thirds |
Deg. | Min. 1 Sec. CO DO OD
Deg. | Min. 1 Sec.

Degrees
Hours | Min. 1 Sec.

Min. 1 Sec. 1 Cros
Min. | Sec. | Thirds

| Thirds
Thirds
Thirds on

11 15 10 15 31 7 45|| 110 4 312 470440
2 301 20 30321 8 0 210 813212

8

80 5201 3 45 30 45,351 8 15 30 12|3312 12 901 610) 4 601 411 034 8 3011 410 16 3412 16 100 640 5 75 51 15 35 8 45

50 20 3512 2011101 720

6 90 61 30 36 9 60 24 3612 24 120 8 0
7105 71 4537| 9 151 710 2815712 281301 401
8120 82 038 9 30 80 32 3512 33140 9/201

911351 9121539/ 9 451 910 36 392 36150
110 150 102 3040110 0 100 40 402 40 160 1040

111651112 454110 15 110 44 412 44 1701120
12180123 04210 30 120 48422 48 180 121 0
13 195|1313 1543110 45|130 52 4312 52 190/1240
142101143 3044/11 0 1410 561442 56/20011320
15225153 45 45 11 15151 0 4513 0 210 14 0

16240 164 046 11 3016 1 4 463 41220 1440
17 255 17 4 1547 11 45 17 1 8473

81230 15 20
18 270184 30 48 12 0 181 124813 12 240 16 0)
192851914 4549/12 15191 16 4913 16.250 16 40
20300/2015 0 50 12 30 201 20:50 3 201260 17 20

21/315 21 5 15 5112 45 21 1 24 51 3 24 27018 0
22/330/2215 3052 13 0 221 28152 3 28128018140
23|345 235 45/55/13 15 23 1 321533 392901920
24360 246 0 54 13 30 24 1 36 543 36 300200
25 3752516 15/55 13 45251 40 55 3 40/310,20 40

26390266 30 56114 0 261
27, 405 27 6 45 5714 15 271
28 42012817 058 14 30 281
129 430/29 7 15 59 14 45291
130|45013017 30/60/15 0:13012

441563 44 320 21 20
48 573 45 3301220
52583 5234022 40
56593 56 35023 201
0 604 0]360 241 01

These are the tables mentioned in the 208th Ar. ticle, and are so easy that they scarce require any farther explanation than to inform the reader, that if, in Table I. he reckon the columns marked with asterisks to be minutes of time, the other columns give the equatorial parts or motion in degrees and minutes; if he reckon the asterisk-columns to be se. conds, the others give the motion in minutes and seconds of the equator; if thirds, in seconds and thirds: And if in Table II. he reckon the asterisk. columns to be degrees of motion, the others give the time answering thereto in hours and minutes; if minutes of motion, the time is minutes and seconds; if seconds of motion, the corresponding time is given in seconds and thirds. An example in each case will make the whole very plain.

EXAMPLE I.

EXAMPLE II. In 10 hours 15 mi. In what time will 153 nutes 24 seconds 20 degrees 51 minutes 5 sethirds, Qu. How much conds of the

equator of the equator revolves revolve through the methrough the meridian? ridian? Deg. M. S.

H. M.S. T. Hours 10 150 0 0 S 150 10 0 0 Min. 15 3 45 0

3 12 0 0 Sec. 24

6 0 Min. 51 3 24 0 Thirds 20 5 Sec. 5

20

Deg. { 159 10 0 0

[blocks in formation]

Sidercal

days shor. 221.

ter than

T:

HE stars appear to go round the Earth

in 23 hours 56 minutes 4 seconds, and solar days, the Sun in 24 hours : so that the stars gain three and why. minutes 56 seconds upon the Sun every day, which

[ocr errors]

amounts to one diurnal revolution in a year; and Plate III. therefore, in 365 days, as measured by the returns of the Sun to the meridian, there are 366 days, as measured by the stars returning to it: the former are called solar days, and the latter sidereal days.

The diameter of the Earth's orbit is but a physical point in proportion to the distance of the stars; for which reason, and the Earth's uniform motion on its axis, any given meridian will revolve from any star to the same star again in every absolute turn of the Earth on its axis, without the least perceptible difference of time shewn by a clock which goes exactly true.

If the Earth had only a diurnal motion, without an annual, any given meridian would revolve from the Sun to the Sun again in the same quantity of time as from any star to the same star again ; because the Sun would never change his place with respect to the stars. But, as the Earth advances almost a degree eastward in its orbit in the time that it turns eastward round its axis, whatever star passes over the meridian on any day with the Sun, will pass over the · same meridian on the next day when the Sun is al. most a degree short of it; that is, 3 minutes 56 seconds sooner. If the year contained only 360 days, as the ecliptic does 360 degrees, the Sun's apparent place, so far as his motion is equable, would change a degree every day; and then the sidereal days would be just 4 minutes shorter than the solar.

Let ABCDEFGHIKLM be the Earth's orbit, Fig. 11. in which it goes round the Sun every year, according to the order of the letters, that is, from west to east; and turns round its axis the same way from the Sun to the Sun again in every 24 hours. Let S be the Sun, and R a fixed star at such an immense distance, that the diameter of the Earth's orbit bears no sensible proportion to that distance. Let Nm be any particular meridian of the Earth, and Na given point or place upon that meridian.

When the Earth is at A the Sun S hides the star R, which would be always hid if the Earth never removed from A; and consequently, as the Earth turns round its axis, the point Nwould always come round to the Sun and star at the same time. But when the Earth has advanced, suppose a twelfth part of its orbit from A to B, its motion round its axis will bring the point N a twelfth part of a natural day, or two hours, sooner to the star than to the Sun, for the angle N B n is equal to the angle ASB: and therefore any star which comes to the meridian at noon with the Sun when the Earth is at A, will come to the meridian at 10 in the forenoon when the Earth is at B. When the Earth comes to C, the point N will have the star on its meridian at 8 in the morning, or four hours sooner than it comes round to the Sun ; for it must revolve from Nton before it has the Sun in its meridian. When the Earth comes to D, the point N will have the star on its meridian at 6 in the morning, but that point must revolve six hours more from No to n, before it has mid-day by the Sun: for now the angle ASD is a right angle, and so is ND n; that is, the Earth has advanced 90 degrees in its orbit, and must turn 90 degrees on its axis to carry the point N from the star to the Sun: for the star al. ways comes to the meridian when N m is parallel to RS A; because D S is but a point in respect to RS. When the Earth is at E, the star comes to the meridian at 4 in the morning; at F, at 2 in the morning; and at G, the Earth having gone half round its orbit, N points to the star R at midnight, it being then directly opposite to the Sun. And therefore, by the Earth’s diurnal motion, the star comes to the meridian 12 hours before the Sun. When the Earth is at II, the star comes to the meridian at 10 in the evening; at I it comes to the me. ridian at 8, that is, 16 hours before the Sun; at K 18 hours before him; at L 20 hours; at M 22; and at A equally with the Sun again.

A TABLE, shewing how much of the Celestial Equator

passes over the Meridian in any Part of a mean SOLAR Day; and how much the Fixed Stars gain upon the mean SolAR TIME every Day, for a Month.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

11 165 27 611 2 45 2741/10 16 41|110 43 15 12 180 29 34 12) 3 0 30 42 10 31 43120 47 11 13195 32 213 3 15 3243 10 46 461|130 51 7 14210 34 3014 3 30 34 4411 1 48|1410 55 3 15/225 36 58 15 3 45 37 45 11 16 51|1510 58 59

16240 39 25 16 4 0 39 4011

31 53||161 2 55 17 255 41 5317| 4 15 41 4711 46 561711 6 50 18270 44 2118 4 30 44 48 12 1 58||18|1 10 46 19 285 46 49 19 4 45 47 49 12 17 191

14 42 20 800 49 17 2015 0 49 50112 32 3201 18 38

21 315 51 4521 5 15 52 5112 47

6211

22 34 22 330 54 12 29 5 30 54 52/13 2 8|di 26 30 23|345 56 40231 5 45 57 53 13 17 11 31 30 26 24 360 59 & 24 6 0 59 54 13 32 13241 34 22 25 376 1 3625 6 16 255 13 47

38 18

[ocr errors]

46 10

120391 4 420 6 31
27|406 6 32/271 6
28 121 3 592917 1
29 136 11 27 291 7 16
30 151 13 55130 7 31

450/14 2 181 142 14
757|14 17 201|2711
9 514 32 23

50 5 11:14 47 25.1291 54

1 14|60|15 2 a 8 goli 57 57

« ElőzőTovább »