Sky and Telescope - January 2016 - 56

OBSERVING

ADAM BLOCK / NOAO / AURA / NSF

Deep-Sky Wonders

MEMOIRS OF THE ROYAL ASTRONOMICAL SOCIETY

After observing
NGC 1535 on multiple evenings in the
winter of 1862 with
a 48-inch reﬂector, William Lassell
described it as "a
very remarkable
Planetary Nebula,"
with a nucleus that
didn't "seem stellar,
but a small patch of
bright light."

by at least 400 times the Earth-Sun distance, a combination that keeps the dwarf well out of the primary's
glare from our vantage point on Earth. This petite star
is only 1½ times the diameter of the Earth, yet it weighs
in at half the mass of the Sun. A white dwarf is the
collapsed core of a low- to intermediate-mass star that
shed much of its substance during the late stages of its
life. No longer generating heat, a white dwarf will cool

until it becomes a "black dwarf." This process takes such
an incredibly long time that our universe isn't yet old
enough to contain any black dwarf stars.
The ruddy companion is a red dwarf star merely
one-ﬁfth the mass of our Sun. The red dwarf and the
system's primary are both main-sequence stars, still fusing hydrogen to helium in their cores. Since high-mass
stars have shorter main-sequence lives than low mass
stars, the burned-out white dwarf must once have been
the trinary's brightest and most massive star.
The golden primary star holds a pop-culture claim to
fame. In the world of science ﬁction, it's the star that the
planet Vulcan orbits in the television and movie universe
of Star Trek.
South of Omicron2 you'll ﬁnd yellow-orange 39
Eridani, and if you drop the same distance southward
again, you'll come to a splendid planetary nebula, NGC
1535. It bears the captivating nickname Cleopatra's Eye,
coined by amateur/professional astronomer Greg Crinklaw. Let's see why.
Cleopatra's Eye announces its presence in the form
of a tiny, bluish disk through my 130-mm scope at 23×.
At 164× it shows a fairly bright central star in a bright,
slightly oval (northeast-southwest) ring that's nested in
a wide, modestly bright, outer halo. The nebula is very
pretty at 234×. Its central star is plainly visible, and its
ring has an ashen, blue-green cast. The ring's outer border is well-deﬁned, but its inner edge is rather indistinct.
I estimate the nebula's dimensions as roughly ¾′ × 2/3′.
Switching to my 10-inch reﬂector at 220×, the hollow surrounding the central star doesn't seem to be a uniform,
round hole so much as a region mottled with darker
patches. Can you imagine Cleopatra's blue and green eye
shadow and the seductive star-twinkle in her eye?

Swimming in the Celestial Stream
Object
ο2

Eri

Type

Mag(v)

Size/Sep

RA
04h

Dec.

15.3m

-07° 39′

Triple star

4.5, 10.0, 11.5

82″ (A, BC), 9.0″ (BC)

NGC 1535

Planetary nebula

9.6

48″ × 42″

04h 14.3m

-12° 44′

NGC 1618

Spiral galaxy

12.7

2.3′ × 0.8′

04h 36.1m

-03° 09′

3.6′ × 0.7′

04h

46.6m

-03° 11′

04h

37.1m

-03° 18′

NGC 1622

Spiral galaxy

12.5

NGC 1625

Spiral galaxy

12.3

2.1′ × 0.5′

55 Eri

Double star

6.7, 6.8

9.3″

04h 43.6m

-08° 48′

NGC 1421

Spiral galaxy

11.4

3.5′ × 0.9′

03h 42.5m

-13° 29′

Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than the cataloged value and varies
according to the aperture and magniﬁcation of the viewing instrument. Right ascension and declination are for equinox 2000.0.

Januar y 2016 sky & telescope

Sky and Telescope - January 2016

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