Telescopic Work for Starlight Evenings

by William F. Denning

[Abbreviations in col. 9:—β., Burnham; T., Tarrant; S., Schiaparelli; L., Leavenworth; E., Engelmann; P., Perrotin; Hσ., H. Struve; M., Maw.]

No.	Name of Star.	Posit;­ion, 1890.				Mags.	Position- Angle	Distance.	Epoch.	Ob­ser­ver.
		R.A.		Dec.
		h	m	°	′		o	″
1.	δ Equulei	21	9·1	+9	34	4½ 5	189·9	0·25	1887·7	β.
		Most rapid binary known. Period 11½ years(Wrublewsky). Disc. 1852 by O. Struve.
2.	Piazzi 109	1	51·0	+1	20	7 7	206·3	0·28	1888·1	S.
		An excessively close and difficult object.Binary.
3.	β Delphini	20	32·4	+14	13	3½ 5½	310·1	0·29	1888·6	β.
		A rapid binary. Period 26 years (Doubjago).
4.	γ2 Andromedæ	1	57·1	+41	48	5 6	277·6	0·35	1884·8	L.
		Distance in Oct. 1889 less than 0″·1, and verydifficult with 36-inch (Burnham).
5.	γ Coronæ Bor.	15	38·1	+26	39	4 7	126·6	0·38	1887·5	S.
		A close binary. Period 95½ years (Doberck).Colours greenish-white and purple.
6.	55 Tauri	4	13·6	+16	16	6½ 8	76·4	0·43	1887·6	S.
		A binary. Difficult object with a 10-inch.
7.	λ Cassiopeiæ	0	25·7	+53	55	6½ 6½	146·9	0·45	1887·3	T.
		Another close binary. Distance of componentsshows little change.
8.	ζ Boötis	14	35·9	+14	12	4 4	293·4	0·51	1887·5	S.
		A binary pair, of equal mags. Period 127years (Doberck).
9.	42 Comæ Bor.	13	4·7	+18	7	5½ 6	189·6	0·55	1889·1	L.
		A close binary, of short period; about 25-3/4years. Disc, in 1827 by O. Struve.
10.	λ Cygni	20	43·1	+36	8	5 7½	70·6	0·63	1888·8	Hσ.
		A binary. The distance between the componentsis increasing.
11.	ζ Coronæ Bor.	15	18·7	+30	41	5½ 6	178·5	0·63	1886·5	T.
		A well-known binary, of short period; 41½years (Doberck).
12.	ω Leonis	9	22·6	+9	32	5½ 7	96·8	0·70	1889·1	L.
		A close pair, but not difficult. Binary.Period 114½ years (Doberck).
13.	15 Lyncis	6	47·8	+58	34	5 6	5·9	0·77	1890·3	M.
		A probable binary, the position and distanceexhibiting a gradual increase.
14.	ι Orionis	5	1·9	+8	21	5½ 7	193·9	0·99	1889·0	L.
		Triple. A low power shows many stars here.
15.	ζ Cancri, A.B.	8	5·9	+18	0	5 6	40·3	1·05	1889·2	L.
		A triple star. A.C. Pos. 134°·4; Dist. 5″·36;Mag. 7; 1878·3 (Hall).
16.	ν Scorpii, A.B.	16	5·6	-19	10	4 7	9·3	1·08	1886·5	T.
		A quadruple star, forming one of the finestsystems in the sky.
17.	π Cephei	23	4·4	+74	47	5 7½	32·5	1·16	1888·7	Hσ.
		Binary. Becoming more difficult with decreaseof distance. Yellow and purple.
18.	ε Arietis	2	52·9	+20	54	5½ 6	202·2	1·28	1889·7	L.
		Distance increasing. Good dividing-test fora 4-inch aperture (T.).
19.	λ Ophiuchi	16	25·4	+2	13	4½ 5½	42·6	1·55	1888·4	L.
		Binary, but period not yet ascertained withaccuracy. Yellow and bluish.
20.	ζ Herculis	16	37·1	+31	48	3 6½	65·8	1·68	1890·7	M.
		A fine, rather close binary. Period 34½ years(Doberck). Single in 1865. Yellow and red.
21.	ξ Ursæ Maj.	11	12·3	+32	9	4 5	222·7	1·63	1889·3	S.
		One of the first-computed binaries. Period63 years (Breen). Excellent object.
22.	δ Cygni	19	41·5	+44	52	3 8	317·7	1·66	1885·5	T.
		A well-known binary. Period 376·7 years(Gore). Test for 4½-inch. Pale yellow and sea-green.
23.	33 Orionis	5	25·5	+3	12	5 6	32·8	1·81	1887·1	T.
		Just visible in a 3-inch. White and paleblue.
24.	θ Aurigæ, A.B.	5	52·2	+37	12	3 8	2·5	1·98	1885·1	T.
		A similar pair to δ Cygni, though the distanceis wider.
25.	70 Ophiuchi	18	0·0	+2	32	4 6	348·7	2·16	1889·3	β.
		Binary. Period nearly 88 years (Gore). Goodobject for a 3-inch. Yellow and purple.
26.	ι Leonis	11	18·2	+11	8	4½ 7½	62·0	2·56	1889·2	L.
		Binary; but distance shows little variationsince 1839. Yellowish and blue.
27.	ε Boötis	14	40·2	+27	32	3 5½	328·1	2·88	1885·4	T.
		A very interesting object, and visible in asmall instrument.
28.	α Scorpii	16	22·7	-26	11	1 8	271·7	2·92	1880·0	β.
		This pair forms an atmospheric rather thanan optical test.
29.	γ Ceti	2	37·6	+2	46	3 7	289·7	2·94	1883·9	P.
		A binary system. Test for a 2½-inch. Yellowand blue.
30.	α Piscium	1	56·3	+2	14	5 6	321·9	3·03	1886·9	T.
		A probable binary, but since 1831 not muchchange in position or distance.
31.	ζ Aquarii	22	23·1	-0	35	4 4	325·8	3·08	1889·9	L.
		A fine binary, with very long period. 1625years (Doberck).
32.	ε1 Lyræ	18	40·7	+39	34	4½ 6½	15·3	3·24	1877·4	Doberck
33.	ε2 Lyræ	18	40·7	+39	30	5 5	137·6	2·45	1877·4	Hall.
		{These stars form a wide double (distance3′ 27″), just separable by the naked eye. A 2½-inch shows a fine double-double.A 4-inch reveals three faint stare between.
34.	ε Hydræ	8	41·0	+6	49	4 7	226·5	3·16	1889·1	β.
		A new comes, Pos. 154°·4; Dist. 0″·26; Mag.6, 1889; 36-inch, power 3300! β.
35.	γ Leonis, A.B.	10	13·9	+20	24	2 4	114·6	3·51	1889·3	β.
		A fine binary. Period 407 years (Doberck).Readily seen in a 3-inch.
36.	δ Serpentis	15	29·6	+10	55	3 5	189·9	3·52	1886·6	Ball.
		Probably binary. Fine object in small instruments.
37.	α Canis Maj.	6	40·36	16	34	1 10	359·7	4·19	1890·3	β.
		Brilliant binary. Period 58·5 years (Gore).Colours white and yellow.
38.	α Herculis	17	9·6	+14	31	3 4½	114·5	4·58	1885·5	T.
		A splendid object. Orange and bluish green.
39.	ζ Cassiopeiæ	0	42·4	+57	14	4 8	184·7	4·76	1888·3	M.
		Binary. Period 195 years (Gruber). Difficultobject for 2-1/4-inch (Johnson).
40.	γ Virginis	12	36·1	-0	51	3 3	153·9	5·45	1889·3	L.
		Well-known binary. Period 182 years (J.Herschel). Single in 1836.
41.	α Geminorum	7	27·6	+32	8	2 3	229·4	5·68	1889·2	L.
		Very fine object. Binary; Period doubtful(Mädler 232 years, Doberck 1001 years).
42.	π Boötis	14	35·6	+16	54	4 6	104·3	6·04	1885·4	T.
		This pair has exhibited little change in pos.or dist. since 1781.
43.	α2 Capricorni, A.B.	20	11·9	-12	53	3 15	149·7	6·30	1879·7	β.
		Good light-test for 6-inches. Companiondouble; pos. 240°, dist. 1′·5.
44.	δ Geminorum	7	13·5	+22	11	3½ 9	207·2	6·98	1886·1	T.
		Rather wide pair of unequal mags. Difficultwith small apertures.
45.	γ Arietis	1	47·5	+18	45	4½ 5	178·3	8·78	1886·9	T.
		A fine, easy object. Discovered in 1664 byHooke.
46.	ι Ursæ Maj.	8	51·7	+48	28	3 12	356·7	9·56	1883·4	E.
		Well seen in a 4-inch, powers 80 and 130.Good light-test.
47.	β Orionis	5	9·3	-8	20	1 9	202·0	9·61	1887·2	T.
		A fine object for small instruments. Visiblein a 2-inch refractor.
48.	γ1 Andromedæ	1	57·1	+41	48	3 6	62·6	10·50	1876·0	Hall.
		A splendid pair, stationary in relativepositions (see no. 4).
49.	γ Delphini	20	41·6	+15	44	4 6	271·2	11·35	1879·7	Hall.
		Estimates of the colour of this pair differ, andchange is inferred.
50.	σ Orionis, A.D.	5	33·2	-2	40	4 10½	236·8	11·62	1875·2
		Multiple. Fine group here. Schröter saw 12stars, Struve 18.
51.	β Scorpii	15	59·0	-19	30	2 5½	26·7	12·72	1879·7	β.
		The brighter star is a close double; Pos. 87°,Dist. 0″·73 (Burnham).
52.	ζ Ursæ Maj.	13	19·5	+55	30	2 4	150·5	14·38	1886·2	T.
		Fine object for small instruments. Otherstars in the field.
53.	α Centauri	14	32·1	-60	23	1 2	202·9	17·12	1888·6	S.
		A fine southern binary with Period of 80·3years (Elkin).
54.	α Ursæ Min.	1	18·5	+88	43	2 9	210·1	18·60
		Good test for a 2-inch. Dawes saw it with1-3/10-inch, Ward with 1-1/4 inch.
55.	61 Cygni	21	2·0	+38	12	5 6	121·0	20·58	1887·7	S.
		Probably a binary of long period (782½ years,Peters; 1159 years, Mann).
56.	33 Arietis	2	34·3	+26	35	5 8	0·3	29·76	1879·7	β.
		A distant and easy pair in small instruments.
57.	β Cygni	19	26·3	+27	44	3 7	55·1	34·32	1879·7	β.
		A beautiful pair, colours golden yellow andsmalt blue.
58.	β Geminorum	7	38·6	+28	18	2 14	274·9	43·00	1877·9	β.
		Disc. by Burnham, who also finds the companiondouble; dist. 1″·4 (1879·2).
59.	α´ Capricorni	20	11·9	-12	53		219·7	44·55	1879·7	β.
		α1 and α2 Capricorni (No. 43) form a naked-eyedouble; Pos. 291°, Dist. 373″·4.
60.	α Canis Min.	7	33·6	+5	30	1 14	317·3	44·62	1877·9	β.
		Difficult object; just seen steadily by Daweswith 8-1/4-inch refractor.
61.	β Lyræ, A.B.	18	46·0	+33	14	3 7	148·9	45·20	1886·9	T.
		There are three other faint and distant components.
62.	α Lyræ	18	33·2	+38	41	1 11	156·1	48·00	1879·7	β.
		Good light-test for a 3-inch. There are othermore distant companions.
63.	α Cassiopeiæ	0	34·3	+55	56	2 13½	280·2	61·33	1879·7	β.
		The 36-inch refractor shows a very faint comes;Dist. 17″·5 (Burnham).
64.	α Canis Maj.,	6	40·3	-16	34	1 13	114·9	71·39	1877·5	Hall.
		This faint and distant companion to SiriusA.C. was disc. by Marth.
65.	α Andromedæ	0	2·7	+28	29	2 11	271·6	71·60	1878·6	G.
		A wide double, visible in a 3-inch, but comesvery faint.
66.	α Tauri	4	29·6	+16	17	1 12	34·1	114·96	1879·7	β.
		Good light-test for a 3-inch. Very faint comesPos. 109°; Dis. 30″·4 (Burnham).

The determination of the angles of position and distance of double stars forms a very important and extensive branch of work in connection with sidereal astronomy. In cases where double stars preserve stationary places relatively to each other, there is clearly no need for frequent re-observation. But in those numerous instances where the two components form a binary system it is desirable to obtain as many measures as possible, so as either to verify the calculated orbit or to furnish the materials for an orbit if one has not been computed before. Dr. Doberck, whose name is well known in these researches, mentioned, in 1882, that ample data for purposes of computation had not been secured for more than thirty or forty binaries out of between five and six hundred such systems that were probably known to exist. Sir W. Herschel, in 1803, estimated the period of revolution of α Geminorum as 342 yrs. 2 mths. and of γ Virginis as 1200 yrs. Orbits[57] do not appear, however, to have been computed until 1827, when Savery of Paris showed that the companion of ξ Ursæ Majoris was revolving in an ellipse with a period of 58-1/4 years. The accomplished Encke also turned his attention to this work, and adopted a more elaborate method; and many others have pursued the subject with very interesting and valuable results. On pp. 302-305 is a selected list of some of the most noteworthy double and binary stars, arranged according to the distance between the components.

In compiling the above list, I have used some of the latest measures available, as most of these doubles are binary systems, and therefore in motion, so that a few years effect a perceptible difference in the angles of position and distance of the components. Some of the pairs are closing up, others are opening, and thus it happens that a binary star, divided with great difficulty to-day, may become an easy object some years hence, and vice versâ. In fact, as telescopic tests they are constantly varying.

Before leaving this part of the subject it may be interesting to refer individually to a few brilliant examples of double stars.

α Canis Majoris (Sirius). A red star according to ancient records, but it is now intensely white. In 1844 Bessel inferred from certain little irregularities in the proper motion of this star that it consisted of a binary system with a period of about half a century[58]. Peters confirmed this idea in 1851, and it was observationally verified eleven years afterwards. On Jan. 31, 1862, Alvan Clark, jun., while testing a new 18½-inch refractor, discovered a very faint companion 10″ distant. Measures in the few subsequent years proved that the position-angle was decreasing, while the distance showed a slight extension. In 1872 it was about 11″·50, but since then the two stars have been approaching each other, and Mr. Burnham’s measures in April 1890 gave the distance as only 4″·19. It is now, therefore, a very difficult object, and only visible in large instruments. In England it is never easy, owing to its southern position, and it has been little observed, but it is satisfactory to note that the large refractors at Washington, Princeton, and Chicago, U.S.A., have been often employed on this object in recent years. Mann gives a period of 51·22 years for this interesting binary, and places the time of periastron-passage as 1890·55. This differs from Gore’s orbit, quoted in the table.

β Orionis (Rigel). A favourite test-object for small instruments. The companion has been seen with only 1½-inch aperture by experienced observers familiar with the object, and accustomed to its appearance in larger telescopes. The beginner may, however, esteem himself fortunate if he distinguishes the smaller star with 3 inches of aperture. When he has done this he may afterwards succeed with 2½ inches only, and quite possibly with 2 inches. He can ascertain his ability in this direction by inserting cardboard diaphragms of the diameters referred to in the dew-cap of his telescope. This object is not a binary; the component stars are fixed relatively to each other, and merely form an optical double. The colours are pale yellow and sapphire blue. Burnham thought the smaller star was elongated, as though a very close double, but the 36-inch at Mount Hamilton has disproved the idea.

α Lyræ (Vega). Another well-known object, and one upon which amateurs are constantly testing their means. The companion star is extremely faint, and small instruments would have no chance with it but for its comparatively wide distance from Vega. Were it much nearer it would be obliterated in the glare. This is a more difficult pair than that of Rigel, though certain lynx-eyed observers have glimpsed the minute star with ridiculously small apertures. It is no mean feat, however, to discern the star with a 3-inch telescope. Webb saw it more easily with a power of 80 than with 144 on a 3-7/10-inch. There are many other stars in the same field, though more distant than the companion alluded to. With power 60 on my 10-inch reflector, I counted eighteen stars in the field with Vega on Oct. 9, 1889, though the full Moon was shining at the time. Several faint stars have been alleged to exist much closer to Vega than the well-known comes; but these have resisted the great American refractors, and it may be safely assumed that they were ghosts produced by a faulty image.

α Ursæ Minoris (Polaris). This double, from its constant visibility in northern latitudes, from its unvarying brightness, and from the relatively stationary positions of the stars composing it, forms an excellent test for small instruments. But it is a comparatively easy object, and ought to be seen in a 2-inch telescope. With this aperture the primitive efforts of a young observer will probably be disappointing. If possible he should first look at the pair through a 3-or 4-inch, and then he will know exactly what he may expect to see with inferior means. A difficult object is often readily glimpsed in a small telescope after the eye has become acquainted with it in a larger one. Experience of this kind is very requisite, and it is by thus educating the eye that observers are gradually enabled to reach objects which appeared hopelessly beyond them at their first attempts. The companion to Polaris, like that of Rigel and Vega, though situated in nearly the same line of sight is not physically related to the larger star, the contiguity of the objects being accidental. Some dubious observations have been made of comites nearer to Polaris than the one to which we have been adverting; but Burnham does not see these, and we are forced to conclude that they have no objective existence.

α Scorpii (Antares). A fiery-red star, with a rather close, faint companion. This object being in 26° of S. declination is rarely seen with advantage in places with latitudes far north. Atmospheric disturbance usually affects the image in such degree that the smaller star is merged in the contortions of the larger. This pair is, however, interesting from the circumstance that it is frequently liable to occultation by the Moon. A night on which this double star can be distinctly seen may be regarded as an exceptional one in point of definition. It appears to have been discovered nearly half a century ago by Grant and Mitchel.