On Certain Changes Which Appear to Have Taken Place in the Positions of Some of the Principal Fixed Stars

XXXI. On certain changes which appear to have taken place in the positions of some of the principal fixed Stars. By John Pond, Astronomer Royal, F. R. S. Read June 19, 1823. Since the date of my last communication on the subject of the deviation of the fixed stars from their computed or predicted places, I have been induced to examine such intermediate observations, as appeared likely to throw some light on this difficult subject. The observations that best deserve attention since the time of Bradley, are the few which were made by the French astronomers, in their Trigonometrical Operations, about the year 1793, and those of Greenwich, Armagh, Westbury and Palermo, some years later, as published in the Philosophical Transactions for the year 1806. As the computations and tables relating to this investigation are subjoined, it will only be requisite, briefly, to state the result. It appears to me, that these observations greatly add to the probability that some variation, either continued or periodical, takes place in the sidereal system, which, producing but very small deviations in a finite portion of time, has hitherto escaped notice. That in consequence of this, it becomes impossible, even if two perfectly exact observations of a star could be made at distant intervals, either by interpolation to assign its place for any intermediate period, or to predict its place for the future, contrary to the theory hitherto received. The nature of this motion appears to be such, that the stars are now mostly found a considerable quantity to the southward of their computed or predicted places. With respect to the laws by which these motions are governed, the observations in question are not sufficiently exact to throw any light upon them. Upon this very difficult point we must, I am inclined to think, rely chiefly, if not entirely, on the Greenwich observations; and as I have already fully discussed this question in my former Paper, I am unwilling, particularly at this advanced period of the season, to trespass any longer on the attention of the Royal Society. in the position of some of the principal fixed Stars. TABLE I. | | Greenwich. 1800. | Armagh. | Palermo. | Westbury. | Westbury's 2 feet Circle. | Promiscuous Observations. | Mean of 4 Catalogues. | |---|-----------------|---------|----------|-----------|---------------------------|---------------------------|------------------------| | 1 | Polaris | 0 | " | " | " | " | " | | 2 | β Ursae Min. | " | " | " | " | " | " | | 3 | β Cephei | " | " | " | " | " | " | | 4 | α Ursae Maj. | " | " | " | " | " | " | | 5 | α Cephei | " | " | " | " | " | " | | 6 | α Cassiopeia | " | " | " | " | " | " | | 7 | γ Ursae Maj. | " | " | " | " | " | " | | 8 | γ Draconis | 38 28 54,0 | 54,0 | 54,0 | 54,0 | 38 28 54,0 | | | 9 | α Persei | " | " | " | " | " | " | | 10| Capella | 44 13 21,5 | 21,5 | 21,0 | 18,7 | 18,0 | 44 13 20,1 | | 11| Cygni | 45 25 41,4 | 39,5 | 38,7 | 37,2 | 45 25 39,2 | | | 12| Lyra | 51 23 41,1* | 37,3 | 37,7 | 36,2 | 35,0 | 51 23 36,5 | | 13| Castor | 57 41 15,0 | * 9,5 | 13,5 | 14,2 | 57 41 14,2 | | | 14| Pollux | 61 30 10,9 | 5,3 | 11,7 | 13,9 | 61 30 12,2 | | | 15| β Tauri | 61 34 32,1 | 32,5 | 33,0 | 33,9 | 61 34 32,9 | | | 16| Andromeda | 62 0 47,0 | 45,2 | 49,5 | 50,2 | 62 0 48,0 | | | 17| Cor. Bor. | 62 36 11,7 | * 7,5 | 10,5 | 13,2 | 62 36 11,8 | | | 18| Arietis | 67 29 21,8 | 23,5 | 22,0 | 20,6 | 67 29 22,0 | | | 19| Arcturus | 69 46 10,8 | 11,2 | 10,2 | 7,7 | 69 46 10,0 | | | 20| Aldebaran | 73 54 20,0 | 18,5 | 16,5 | 15,7 | 73 54 17,7 | | | 21| β Leonis | 74 18 37,9 | 34,2 | 33,8 | 32,7 | 74 18 34,7 | | | 22| Herculis | " | " | " | " | " | " | | 23| Pegasi | 75 52 0,5 | 1,3 | 1,4 | 58,2 | 75 52 0,2 | | | 24| γ Pegasi | 75 55 39,8 | 37,7 | * 41,9 | 37,2 | 75 55 38,2 | | | 25| Regulus | 77 3 38,8 | * 32,2 | 36,5 | 34,2 | 77 3 36,5 | | | 26| Ophiuchi | 77 16 57,8 | 53,6 | 55,5 | 53,7 | 77 16 55,1 | | | 27| Aquilæ | 81 38 56,2 | 50,8 | 53,3 | 51,7 | 81 38 53,0 | | | 28| Orionis | 82 38 35,0 | 32,0 | 33,5 | 31,7 | 82 38 33,0 | | | 29| Serpentis | 82 56 5,4 | * 0,0 | 4,8 | 2,4 | 82 56 4,2 | | | 30| Procyon | 84 16 21,7 | 19,5 | 20,0 | 21,7 | 84 16 21,1 | | | 31| Ceti | 86 42 10,4 | 7,5 | 9,7 | 10,4 | 86 42 9,5 | | | 32| Aquarius | 91 17 4,6 | 4,8 | 4,6 | 4,8 | 91 17 4,7 | | | 33| Hydræ | 97 47 54,3 | 49,0 | 53,0 | 53,2 | 97 47 52,4 | | | 34| Rigel | 98 26 34,2 | 33,2 | 34,9 | 36,7 | 98 26 34,7 | | | 35| Spica Virg. | 100 6 42,7 | 39,0 | 42,5 | 43,2 | 100 6 41,9 | | | 36| Capricorn | 103 9 9,1 | 13,5 | 8,7 | 8,2 | 103 9 9,9 | | | 37| Sirius | 106 27 2,3 | 5,3 | 4,7 | 2,2 | 106 27 3,1 | | * These are omitted in the calculations. Mr. Pond on certain changes which appear to have taken place TABLE II. | Star Name | N.P.D. 1756 | N.P.D. 1800 | Motion in 44 Years | Motion in 22 Years | Correction | Ann. Var. 1811 X 22 | Predicted N.P.D. 1822 | Stars observed South of predicted Place | |-----------------|-------------|-------------|--------------------|--------------------|------------|---------------------|-----------------------|----------------------------------------| | Polaris | | | | | | | | | | β Ursae Min. | 14 50 49.0 | | | | | | | | | β Cephei | 20 30 22.9 | | | | | | | | | α Ursae Maj. | 26 56 16.7 | | | | | | | | | α Cephei | 28 26 28.7 | | | | | | | | | Cassiopeia | 34 48 17.4 | | | | | | | | | γ Ursae Maj. | 34 56 56.4 | | | | | | | | | γ Draconis | 38 28 21.2 | 38 28 54.0 | + 0 32.8 | + 0 16.4 | -1.5 | + 0 14.9 | 38 29 8.9 | + 0.9 | | γ Ursae Maj. | 39 27 40.2 | | | | | | | | | α Persei | 41 4 47.8 | | | | | | | | | Capella* | 44 16 51.0 | | | | | | | | | Cygni* | 45 34 51.9 | | | | | | | | | Lyre* | 51 25 46.6 | | | | | | | | | Castor | 57 36 10.2 | | | | | | | | | Pollux | 61 24 27.9 | | | | | | | | | β Tauri | 61 37 30.4 | | | | | | | | | Andromeda | 62 15 26.8 | | | | | | | | | Cor. Bor. | 62 26 59.7 | | | | | | | | | Arietis | 67 42 12.4 | | | | | | | | | Arcturus | 69 32 13.2 | | | | | | | | | Aldebaran | 74 0 14.9 | | | | | | | | | β Leonis | 74 3 55.1 | | | | | | | | | Herculis | 75 18 45.6 | | | | | | | | | Pegasi | 76 6 10.2 | | | | | | | | | γ Pegasi | 76 10 25.7 | | | | | | | | | Regulus | 76 51 4.7 | | | | | | | | | Ophiuchi | 77 14 35.4 | | | | | | | | | Aquilae | 81 45 27.3 | | | | | | | | | Orionis | 82 39 41.8 | | | | | | | | | Serpentis | 82 47 24.2 | | | | | | | | | Procyon | 84 10 19.8 | | | | | | | | | Ceti | 86 52 57.7 | | | | | | | | | Aquarii | 91 29 41.4 | | | | | | | | | Hydrea | 97 36 50.2 | | | | | | | | | Rigel | 98 30 10.9 | | | | | | | | | Spica Virg. | 99 52 48.3 | | | | | | | | | Capricorn | 103 16 53.0 | | | | | | | | | Sirius | 106 23 56.7 | | | | | | | | Dr. Maskelyne considered the determination of these three stars as erroneous, and assigned corrections amounting to two or three seconds—vide Greenwich Observations. ### TABLE III. | N. P. D. | Westbury, N. P. D. | Motion in 44 Years. | Motion in 22 Years. | Correction. | Ann. Vari. 1811 X 29. | Predicted N. P. D. 1892. | Stars observed South of predicted places. | |----------|-------------------|---------------------|--------------------|------------|-----------------------|-------------------------|----------------------------------------| | | Co-Lat. 38° 31', 21", 0" | | | | | | | | 1 | Polaris | | | | | | | | 2 | β Ursae Min. | 14° 50' 49", 0" | +10° 36", 8" | +5° 23", 9" | +0,2 | +5° 24", 1" | 15° 7' 0", 9" | | 3 | α Cephei | 20° 30' 22", 9" | | | | | | | 4 | α Ursae Maj. | 26° 56' 16", 7" | | | | | | | 5 | α Cassiopeiae | 28° 26' 28", 7" | | | | | | | 6 | γ Ursae Maj. | 34° 48' 17", 4" | | | | | | | 7 | γ Draconis | 34° 56' 56", 4" | | | | | | | 8 | γ Ursae Maj. | 38° 28' 21", 2" | | | | | | | 9 | α Persei | 44° 16' 51", 0" | | | | | | | 10 | Capella | 45° 34' 51", 9" | | | | | | | 11 | Cygni | 44° 16' 51", 0" | | | | | | | 12 | Lyra | 45° 34' 51", 9" | | | | | | | 13 | Castor | 51° 25' 46", 6" | | | | | | | 14 | Pollux | 57° 36' 10", 2" | | | | | | | 15 | Tauri | 61° 24' 27", 9" | | | | | | | 16 | Androm | 61° 37' 30", 4" | | | | | | | 17 | Cor. Bor. | 62° 15' 26", 8" | | | | | | | 18 | Arietis | 62° 26' 59", 7" | | | | | | | 19 | Arcturus | 67° 42' 12", 4" | | | | | | | 20 | Aldebaran | 69° 32' 13", 2" | | | | | | | 21 | Leonis | 74° 0' 14", 9" | | | | | | | 22 | Herculis | 74° 3' 55", 1" | | | | | | | 23 | Pegasi | 75° 18' 45", 6" | | | | | | | 24 | Regulus | 76° 6' 10", 2" | | | | | | | 25 | Ophiuchi | 76° 10' 25", 7" | | | | | | | 26 | Aquila | 77° 14' 35", 4" | | | | | | | 27 | Orionis | 81° 45' 27", 3" | | | | | | | 28 | Serpentis | 82° 39' 41", 8" | | | | | | | 29 | Procyon | 82° 47' 24", 2" | | | | | | | 30 | Ceti | 84° 10' 9", 8" | | | | | | | 31 | Aquarii | 86° 52' 57", 7" | | | | | | | 32 | Hydræ | 91° 29' 41", 4" | | | | | | | 33 | Rigel | 97° 36' 50", 2" | | | | | | | 34 | Spica Virg. | 98° 30' 10", 9" | | | | | | | 35 | Capricor. | 103° 16' 53", 0" | | | | | | | 36 | Sirius | 106° 23' 56", 7" | | | | | | * This determination of Regulus was from two imperfect observations only, and is therefore probably erroneous. Mr. Pond on certain changes which appear to have taken place TABLE IV. | N. P. D. | N. P. D. | Motion in | Motion in | Corrections | Ann. Var. | Predicted | Stars observed | |----------|----------|-----------|-----------|-------------|-----------|------------|---------------| | | Co. Lat. | Mean of 4 | 44 years. | 22 years. | | | | | | | Catalogues.| | | | | | 1 Polaris. 2 β Ursae Min. 3 β Cephei 4 α Ursae Maj. 5 α Cephei 6 Cassiopeia 7 γ Ursae Maj. 8 γ Draconis 9 γ Ursae Maj. 10 α Persei 11 Capella 12 α Cygni 13 α Lyrae 14 Castor 15 Pollux 16 β Tauri 17 α Androm. 18 α Cor. Bor. 19 α Arietis 20 Arcturus 21 Aldebaran 22 β Leonis 23 α Herculis 24 α Pegasi 25 γ Pegasi 26 Regulus 27 α Ophiuchi 28 α Aquilae 29 α Orionis 30 α Serpentis 31 Procyon 32 α Ceti 33 α Aquarii 34 α Hydrae 35 Rigel 36 Spica Virg. 37 α Capricorn. 38 Sirius in the position of some of the principal fixed stars. TABLE V. | | N.P.D. 1800. Interpolated. | N.P.D. 1813. Interpolated. | Ann. Var. 1795. | N.P.D. 1790. | Ann. Var. 1785. | N.P.D. 1780. | |---|-----------------------------|-----------------------------|----------------|-------------|----------------|-------------| | 1 | Cassiopeiae | | | | | | | 2 | Polaris | | | | | | | 3 | Arietis | | | | | | | 4 | Ceti | | | | | | | 5 | Persei | | | | | | | 6 | Aldebaran | | | | | | | 7 | Capella | | | | | | | 8 | Rigel | | | | | | | 9 | Tauri | | | | | | | 10| Orionis | | | | | | | 11| Sirius | | | | | | | 12| Castor | | | | | | | 13| Procyon | | | | | | | 14| Pollux | | | | | | | 15| Hydrae | | | | | | | 16| Regulus | | | | | | | 17| Ursae Maj. | | | | | | | 18| Leonis | | | | | | | 19| Ursae Maj. | | | | | | | 20| Spica Virg. | | | | | | | 21| Ursae Maj. | | | | | | | 22| Arcturus | | | | | | | 23| Ursae Min. | | | | | | | 24| Cor. Bor. | | | | | | | 25| Serpentis | | | | | | | 26| Antares | | | | | | | 27| Herculis | | | | | | | 28| Ophiuchi | | | | | | | 29| Draconis | | | | | | | 30| Lyrae | | | | | | | 31| Aquilae | | | | | | | 32| Cygni | | | | | | | 33| Cephei | | | | | | | 34| Cephei | | | | | | | 35| Aquarii | | | | | | | 36| Pegasi | | | | | | | 37| Andromed. | | | | | | Mr. Pond on certain changes which appear to have taken place TABLE VI. | Names of Stars | Bradley. 1756. | Mayer. 1756. | Mayer corrected. | Difference between Bradley and Mayer. | |----------------|----------------|--------------|------------------|--------------------------------------| | Capella | 44° 16' 51.0" | 44° 16' 49.3" | 52.8" | -1.8 | | α Cygni | 45° 34' 51.9" | 45° 34' 48.4" | 51.9" | 0.0 | | α Lyrae | 51° 25' 46.6" | | 43.6" | -0.5 | | Castor | 57° 36' 10.2" | | 6.9" | -0.2 | | Pollux | 61° 24' 27.9" | | 23.4" | +1.0 | | β Tauri | 61° 37' 30.4" | | 27.7" | -0.8 | | α Androm. | 62° 15' 26.8" | | 22.4" | +0.9 | | α Arietis | 67° 42' 12.4" | | 7.1" | -0.2 | | Arcturus | 69° 32' 13.2" | | 12.8" | -3.1 | | Aldebaran | 74° 0' 14.9" | | 11.9" | -0.5 | | β Leonis | 74° 3' 55.1" | | 53.9" | -2.3 | | α Pegasi | 76° 6' 10.2" | | 5.2" | +1.5 | | Regulus | 76° 51' 4.7" | | 0.0" | +1.2 | | α Ophiuchi | 77° 14' 35.4" | | 32.6" | -0.7 | | α Aquilae | 81° 45' 27.3" | | 23.4" | +0.4 | | α Orionis | 82° 39' 41.8" | | 41.1" | -2.8 | | α Serpentis | 82° 47' 24.2" | | 18.3" | +2.4 | | Procyon | 84° 10' 9.8" | | 8.7" | -2.4 | | α Ceti | 86° 52' 57.7" | | 59.6" | +3.6 | | α Aquarii | 91° 29' 41.4" | | 39.3" | +1.6 | | α Hydrae | 97° 36' 50.2" | | 46.1" | +0.6 | | Rigel | 98° 30' 10.9" | | 9.5" | -2.1 | | Spica Virg. | 99° 52' 48.3" | | 45.2" | -0.4 | | Sirius | 106° 23' 56.7" | | 54.2" | -1.0 | | Antares | 115° 51' 57.3" | | 54.8" | -1.0 | | γ Pegasi | 76° 10' 25.7" | | 22.1" | +0.1 | | 2 α Capricor. | 103° 16' 53.0" | | 49.0" | +0.5 | The French astronomers, in their Trigonometrical Operations, employed six stars, whose declinations for the year 1793, they determined with a singular degree of precision with their repeating circle, viz. N. P. D. 1793 α Draconis $25^\circ 37' 52",05$ ζ Urs. Maj. $33^\circ 59' 21",30$ Capella $44^\circ 13' 50",40$ Pollux $61^\circ 29' 15",20$ β Tauri $61^\circ 35' 0",50$ 1796 β Urs. Min. $15^\circ 0' 40",37^*$ By combining these with Bradley's observations in 1753, I compute their predicted places for 1823, and find them by observation as follows: β Urs. Min. $3",5$ North of its predicted place. α Draconis $3",5$ North. ζ Urs. Maj. $1",3$ South. Capella $6",0$ South. Pollux $4",0$ South. β Tauri $3",0$ South. Sirius $7",0$ South, from a determination of Mechain with the repeating circle in 1800. The above are the best authorities that can be found from the time of Bradley to the year 1813. * The Westbury determination of β Ursæ Minoris differs $2"$ from this; and as the observations were made on the star both above and below the Pole, it merits some confidence. The mean of the French and Westbury Observations give a northern motion equal to $1",7$. Mr. Pond on certain changes which appear to have taken place Computation of the Southern Motion of Capella. 1753. N. P. D. - - - $44^\circ 17' 5''$ Extremely exact; from a computation by Dr. Maskelyne, in his own handwriting. 1793. N. P. D. - - - $44^\circ 13' 50'',40$ Arc du Meridien, page 653. Bradley's refraction. $3^\circ 14', 8''$ Motion in 40 years. $\frac{194''}{40} = 4,870$ An. Var. in 1773. Precession $\left\{ \begin{array}{l} 1773 = 5,193 \\ 1808 = 4,974 \end{array} \right.$ diff. = $0,217$ change of precession in 35 years. $4,653$ An. Var. for 1808. $30^\circ$ $1395', 9'' = 2' 19'',6$ predicted motion in 30 years. 1793. N. P. D. - - - $44^\circ 13' 50'',4$ $2' 19'',6$ $44^\circ 11' 30'',8$ predicted N. P. D. 1823. $44^\circ 11' 36'',8$ observed N. P. D. 1823. $6'',0$ Star south of predicted place in 30 years. in the position of some of the principal fixed stars. Explanation of the preceding Tables. Table I. is nearly the same as published in the Philosophical Transactions for 1806. The Greenwich Catalogue is corrected for flexure, and the other catalogues corrected each by a common quantity, so as to make the polar distance of γ Draconis $38^\circ 28' 54''$, the same as in the Greenwich Catalogue. It may be doubted whether the Palermo Catalogue can, with any propriety, be introduced in this investigation, considering that the observations were made in a different latitude, and computed by a different table of refraction. The discordances in these catalogues are very considerable, and show that very little reliance can be placed even on the most probable mean of them all. Table II. shows the southern motion, as deduced from the Greenwich Catalogue of 1800, corrected for the flexure of the mural quadrant. Table III. in the same manner, shows the southern motion deduced from the Westbury Catalogue. Table IV. shows the southern motion deduced from the mean of all the Catalogues. From this Table it appears, that however doubtful the determination may be, as deduced from any particular star, yet the general tendency of motion to the southward is so obvious, as to leave but little room to doubt of its reality. Table V. contains interpolated places for the years 1780, 1790, 1800, 1813. These Tables are formed upon the supposition that no southern motion exists, but the proper motions of all the stars are uniform: it moreover supposes the present Catalogue for 1823 exact. It has been seen, that it is quite impossible to reconcile the very best catalogues to such a supposition; as has been particularly exemplified in the observations of Greenwich and Dublin for the year 1813. The Greenwich Observations for that year will be found very erroneous, and those of Dublin still more so. Indeed it appears to me that the Dublin observations cannot be placed in a more unfavourable point of view, than by supposing the southern motion in question not to exist. Table VI. contains the Catalogues of Mayer and Bradley; the former is corrected by a common quantity $3''$, which I find necessary to equalize the positive and negative differences.