Sky and Telescope - April 2015 - 37

11h 20m

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THE LARGE 20-FOOT TELESCOPE. The conﬁguration of Herschel's reﬂector changed with time; this
engraving, published by the astronomer in 1794, shows
the system of pulleys manipulated by an assistant to
adjust the declination.

UNIVERSITY OF CAMBRIDGE / INSTITUTE OF ASTRONOMY LIBRARY

Arp; he catalogued the galaxy as Arp 162 in his Atlas of
Peculiar Galaxies (1966).
Herschel encountered the last of the Leo Minor galaxies just a few minutes later. NGC 3486 and NGC 3510
probably form a wide physical pair, but morphologically
they are quite diﬀerent from each other. NGC 3486 is a
large, graceful, multi-arm spiral that appears quite ethereal visually; the bright core is surrounded by a grainy
outer shell with ill-deﬁned edges. NGC 3510 is a wispy,
low surface brightness object that Herschel described as
"faint, much extended, 1.5′ long but very narrow." Almost
1° south of this object is the close pair NGC 3504 and
°
NGC 3512. Both galaxies are bright (11th and 12th magnitude, respectively), and large-aperture telescopes will
show the bar and inner structure of NGC 3504 well. Two
low surface brightness arms emerge from the bar to form
a pseudo ring around it.
A harbinger of things to come next occurred as Herschel encountered three faint members of a distant galaxy
cluster. NGC 3527, NGC 3550, and NGC 3552 are among
the brightest members of the Abell 1185 galaxy cluster
in Ursa Major, some 400 million light-years away from
Earth. Herschel classiﬁed all three as very faint. NGC
3527 is a face-on barred spiral, while NGC 3550 and NGC
3552 are both ellipticals. Two condensations, very likely
companion galaxies, appear in the outer halo of NGC
3550, one to the northeast, the other to the southwest.
In a medium-aperture telescope, these objects appear as
faint, unresolved extensions, but observers may be able to
resolve the companions in large-aperture instruments.
Another gap of 20 minutes followed before Herschel
came upon another wide physical pair. NGC 3713 (in Leo)
and NGC 3714 (in Ursa Major) are both faint, though condensed, objects lying about 300 million light-years away

from us. William had diﬃculty resolving NGC 3714 and
described it to Caroline as "extremely faint. 240 (magniﬁcation) left it doubtful."
Up to this point the Herschels had had a productive
night, recording 19 new nebulae at a steady pace. Things
were now about to get quite busy, though, as William was
about to discover 25 objects in less than 40 minutes.
The ﬁrst three discoveries were NGC 4004, NGC
4008, and NGC 4017, all part of a large, loose group
of galaxies. NGC 4004, shining at magnitude 13.6, is a

10h 50m

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+30°

3550
3552

3486
3527

3510

3400

3265

3380

3504

LEO

3414

3512

3245

3277

3418

MINOR

3451

3196

3274

+28°

LEO
+26°

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Sk yandTelescope.com April 2015

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Sky and Telescope - April 2015

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