The following list includes a number of double and multiple stars,
clusters, and nebulæ, which may be fairly well seen with instruments
up to 3 inches in aperture. A few objects have been added on account
of their intrinsic interest, which may prove pretty severe tests. The
places given are for 1900, and the position-angles and distances
are mainly derived from Mr. Lewis's revision of Struve's 'Mensuræ
Micrometricæ,' Royal Astronomical Society's Memoirs, vol. lvi., 1906.
For finding the various objects, Proctor's larger Star Atlas, though
constructed for 1880, is still, perhaps, the most generally useful.
Cottam's 'Charts of the Constellations' (Epoch 1890) are capital, but
somewhat expensive. A smaller set of charts will be found in Ball's
'Popular Guide to the Heavens,' while Peck has also published various
useful charts. The student who wishes fuller information than that
contained in the brief notes given below should turn to Gore's
exceedingly handy volume, 'The Stellar Heavens.'
The brighter stars are generally known by the letters of the Greek
alphabet, prefixed to them by Bayer. When these are used up, recourse
is had either to the numbers in Flamsteed's Catalogue, or to those in
Struve's 'Mensuræ Micrometricæ.' The Struve numbers are preceded by
the Greek [Sigma]. A few of the more notable variable and red stars
are included; these are generally marked by capital letters, as V.
AQUILÆ. The order of the notes is as follows. First is given the
star's designation, then its place in hours and minutes of right
ascension and degrees and minutes of declination, N. and S. being
marked respectively by + and -; then follow the magnitudes; the
position-angles, which are measured in degrees from the north, or
bottom point of the field, round by east, south, and west to north
again; the distances of the components from one another in seconds of
arc; and, finally, short notes as to colour, etc. According to Dawes,
one inch aperture should separate the components of a 4·56″ double
star, two inches those of a 2·28″, three those of a 1·52″, and so
on. If the observer's glass can do this on good nights there is little
fault to find with it. Double stars may be difficult for other reasons
than the closeness of the components; thus, a faint companion to a
bright star is more difficult to detect than a companion which is not
far below its primary in brightness. Clusters and nebulæ, with a
few exceptions, are apt to prove more or less disappointing in small
instruments. The letters of the Greek alphabet are as follows:
[alpha] Alpha.
[beta] Beta.
[gamma] Gamma.
[delta] Delta.
[epsilon] Epsilon.
[zeta] Zeta.
[eta] Eta.
[theta] Theta.
[iota] Iota.
[kappa] Kappa.
[lambda] Lambda.
[mu] Mu.
[nu] Nu.
[xi] Xi.
[omicron] Omicron.
[pi] Pi.
[rho] Rho.
[sigma] Sigma.
[tau] Tau.
[upsilon] Upsilon.
[phi] Phi.
[chi] Chi.
[psi] Psi.
[omega] Omega.
ANDROMEDA.
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