Sky and Telescope - April 2015 - 36

The Herschel Sprint
William's telescope, the so-called Large 20-Foot, was
ready in the fall of 1783, but because he was working alone
and the instrument was somewhat diﬃcult to use, initial
results were disappointing. In mid-December 1783, he
modiﬁed his search method. First, he set up the telescope
as a transit instrument, aiming it at the meridian. He
hired an assistant to slowly raise and lower the telescope
by 2-3° of declination while the sky's diurnal motion
°
brought new stars into the ﬁeld of view. He used an
eyepiece with a magniﬁcation of 157× and a 15′ 4″ ﬁeld of
view. When necessary, he used a higher magniﬁcation to
conﬁrm his sightings. Typically, he studied the sky for an
hour or more at a time, pausing only when clouds intervened or he needed to reset the telescope for some other
reason. Each one of these sessions was called a "sweep"; a
typical night involved three or four sweeps.
William's second modiﬁcation to his method was his
employment of Caroline, who recorded in a register the
positions and other details of the discoveries he made at
the eyepiece. She used John Flamsteed's catalogue (volume 3 of the Historia Coelestis Britannica) to identify reference stars. This allowed William to spend all his time
at the telescope. These changes in strategy bore immediate results. The small team soon found that the sky was
teeming with undiscovered star clusters and nebulae,
waiting to be revealed.
Fully half of Herschel's discoveries were made in 1784
and 1785. He ardently searched on every clear night and
even when conditions were far from ideal. He often discovered a dozen objects in a single night; on some nights,
he noted many more. By spring of 1785, he and Caroline
were closing in on 1,000 new objects. But on April 11,
1785, they enjoyed a night of discovery never approached
nor equaled in the annals of visual astronomy.
12h 30m

12h 20m

12h 10m

The sweep that night began near the modern-day
border between Leo and Leo Minor, at approximately
10h 00m RA, with the north-south sweep covering about
2½ degrees, centered at about +28° declination (epoch
2000.0). The ﬁrst object encountered was not only the
faintest of the night, but one of the faintest in Herschel's
entire catalogue. NGC 3196 is a high surface brightness,
lenticular galaxy, so very small and remote that William
described it as "extremely faint, a little extended, a little
doubtful." Care and patience are needed to pick up this
14th-magnitude fuzzy; it's situated immediately west of
a quite dim ﬁeld star, which may help in locating it. The
galaxy's high radial velocity implies a distance of about
675 million light-years.
Herschel next encountered a loose quartet of galaxies:
NGC 3245, NGC 3265, and NGC 3277 in Leo Minor,
and NGC 3274 in Leo. The ﬁrst three galaxies are part
of a group associated with NGC 3254 immediately to the
north, discovered by Herschel a month earlier. A glowing
oval of light oriented north-south, NGC 3245 is the brightest of the three objects. NGC 3274, a fuzzy elongation to
the south of NGC 3245, is likely a small spiral galaxy with
an irregular outer structure.
Close to twenty minutes passed before Herschel came
upon another loose clump of galaxies. NGC 3380, NGC
3400, NGC 3414, NGC 3418, and NGC 3451 all have
similar radial velocities and likely form a gravitationally
bound system about 60 million light-years away from
us. Visually, NGC 3414 is the brightest and most interesting of the group, displaying a bright core with faint,
bar-like extensions embedded in a hazy outer envelope.
The extensions ﬂare slightly as the distance from the core
increases, and it's possible that this is a polar ring galaxy.
Its peculiar extensions caught the attention of Halton

12h 00m

11h 50m

11h 40m

11h 30m

+30°
4310

4495
4448

4286 4283
4278

4375

4196
4251

+28°

4393

4131
4169 4132
4175 4174 4134
4173

MAJOR
3714

4185

4104

4008

3713

4004

4275

4017

4475
ALL CHARTS S&T: GREGG DINDERMAN

URSA

4080
4146

LEO

3944

3902

+26°

12h 30m

12h 20m

April 2015 sky & telescope

12h 10m

12h 00m

11h 50m

11h 40m

11h 30m

Sky and Telescope - April 2015

Table of Contents for the Digital Edition of Sky and Telescope - April 2015