How to keep the clock right by observations of the fixed stars with a small fixed telescope ... by Thomas Warner

Author:Thomas Warner
Language: eng
Format: epub
Publisher: Williams and Norgate
Published: 1876-03-25T05:00:00+00:00

Dif,

for 10 m. R, A.

^0149 '0164

*oi79

■0194

*021O ^0215

■^z4T ■0256 ■0271

+ ■0285

In Dec. given in Seconds of Arc.

for 10 m. R, A.

O

I 1

2 2

2

3 3

3 4 4 5 S 6

6

7

7

8

8

9

9 lo

II 12

12

13

H 14 IS 16

16 17 18 18 19 20

Dif.

for ic m A.

O

I I

2 I 2 2

3

2 3 3 4 4 4

S 6

6

6

7 8

8

9 10

10 12

[2 13

H

'S 16 16 18 18 19 *9

The last Decimal in the Sec Vars. may be slightly incorrect

Aw imaginary point in the heayens, the Mean Eqninox, may be said to roTolvo ronnd the earth at an nniform rate, passing the meridian at intervals of 23 h. S^^' 4*090549806 sec. (Shortrede*s table, where the length of an equinoctial day is given in seconds of mean solar time).

The fixed stars also pass the meridian in the order of their Bight Ascensions. The Bight Ascension of a star generally expresses the interval of time between the transit of the equinox and that of the star. Astronomers have at different times observed, and determined with great accuracy, the Bight Ascensions of a groat number of stars, and also their Declinations, or angular distances from the equator.

Those Bight Ascensions are not fixed quantities, since each star, according to its position in the heavens, is subject to noticeable variations in its Bight Ascension.

Those variations may be conveniently arranged in three classes:

ist. With respect to the stars included in Table lY., there is a continual increase in their Bight Ascensions, of from 2 to 4 seconds a year— • Preoossion.*

and. There is a slight fluctuation extending over a period of i8'6 years; the star daring that time gaining and losing upon its mean place—' Lunar Nutation.'

3rd, There are two fluctuations apparent during the year—'Aberration' and * Solar Nutation.*

The laws which govern all these movements have been discovered by aatrouomors, and the movements can be calculated with the greatest certainty; so that for many years to come the time at which a star will apparently pass the meridian on any given day can be predicted to less than a second.

The Tables in this book are intended to enable the observer to calculate with vory little trouble, and with slight chance of error, the mean solar time of tho appivrent transits across the meridian, of the stars included in the list. It will bo 8uffici<uit to show that the Tables are founded upon, and are in aooimlaiUH> with, formulie adopted by the highest authorities.

Table I« has been found by the repeated addition of 23 h. 56 m. 4*09055 sea, tho k>n|tth of an equinoctial day, to 5 h. 13 m. 28 sec., the time opposite Jan. i.

If^ then, tho transit of the equinox took place on that day at 5 h. 13m. 28 sec., tho Table would give tlie time of its transit on all the remaining days in the yxHur. Ihit the oquinox does not pass the meridian of Greenwich so soon as thai, on Jau« 1 in any ytiar mentioned in Table IIL Table I. will consequently leqoire a Oixrrection (or Jan« i, and the remaining days in the same year will require tibe samo iwrreotion.

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