200-INCH HALE TELESCOPE—HUBBLE 187 
successful, except for the large size of the star images produced by 
the poor seeing. The exposure was made on January 26, 1949, about 
10 p. m., after waiting more than a week for a break in the weather. 
The object, NGC2261, is a well-known, variable galactic nebula—a, 
comet-shaped mass with the variable star, R Monocerotis, at the apex. 
Plate 6, S.A. 57; R.A.=13"6"3, Decl.=-+29°37’ (1950); Jan. 27, 
1949; 60 min. exposure, seeing average; enlarged 7% ; center is 2/5 N. 
and 3/4 W. of BD+30°2371. This selected area contains one of the 
most reliable magnitude sequences available for faint stars extending 
to the 21st magnitude. Exposures of 1 minute registered stars to 
about 19.7, and of 3 minutes, to about 20.7. Exposures of 5 or 6 
minutes reached the extreme limits of the 100-inch, beyond the end 
of the sequence. From these data it is estimated that the 60-minute 
exposures permitted by the dark sky above Palomar reached at least 
1.5 magnitude beyond the 100-inch. 
The threshold of the plate is dominated by nebulae rather than by 
stars, and this fact emphasizes the tremendous range of the telescope. 
Some of the faintest nebulae recorded are presumably at about twice 
the distance reached with the 100-inch or, in round numbers, at about 
1,000 million light-years. This figure, of course, refers to average 
nebulae. Individual images on the photograph may represent dwarf 
nebulae at lesser distances or giant nebulae, even more remote. 
Plate 7, Messier 87 (NGC4486); R.A.=12°2873, Decl.=-+12°42’ 
(1950); Apr. 27, 1949; exposure 45 min., seeing average; enlarged 8X. 
The object is one of the brightest members of the Virgo cluster of 
nebulae, whose distance is of the order of 7.5 million light-years. It 
is classified as a peculiar elliptical nebula (KOp). The photograph 
shows the nebula, presumably a globular mass of type II stars (1. e., 
stars similar to those in globular star clusters), surrounded by an 
extensive, tenuous atmosphere of supergiant stars. ‘This phenomenon 
was suggested by the best photographs made with the 100-inch on 
Mount Wilson, but is conspicuous on the 200-inch plate. 
Plate 8, NGC5204; R.A.=13"28"0, Decl.=+ 58°38’ (1950); Jan. 
31, 1949; exposure 30 min., seeing average; enlarged 4X. 
The object is a dwarf, late-type spiral in Ursa Major, at an esti- 
mated distance of less than 3 million light-years. The plate is in- 
cluded to show the ability of the telescope to resolve the neighboring 
stellar systems so that the brighter stars can be studied individually. 
Photographs of several of the larger spirals, such as M 81, NGC2403, 
etc., have been made, but the coma-free field of the telescope at full 
aperture is so small (about 5 minutes of are in diameter) that the 
plates are not suitable for reproduction on a scale sufficient to show 
the resolution to advantage. 
Plate 9, NGC3359; R.A.=10"43"4, Decl.=+63°20’ (1950); Apr. 
27, 1949; exposure 45 min., seeing average; enlarged 3X. 
