Astronomy

BINOCULARUNIVERSE

BY PHIL HARRINGTON

68 ASTRONOMY • APRIL 2018

W

ith the Milky

Way ’s c u r t a i ns

of cosmic dust

drawn away,

the spring sky

window opens toward the deep-

est recesses of the universe. The

view offers us an unparalleled

opportunity to explore the

depths of intergalactic space.

Commanding center stage in

the April sky is Leo the Lion.

Within its boundaries are sev-

eral galaxies bright enough to

see through binoculars, albeit

with some effort.

The two brightest are M65

and M66. They appear just 20'

apart, to the southeast of the

star Theta (θ) Leonis. Theta

marks the right angle in the

triangle of stars forming Leo’s

back and tail.

Charles Messier discovered

M65 and M66 on March 1,

1780. Seven years earlier, on
      November 1, 1773, a comet he
      had discovered passed between
      these two galaxies. Messier’s
      records show he was viewing
      his comet that evening, but he
      “did not see [the galaxies],
      without doubt due to the light
      of the comet.”

To find this galactic pair,

drop 2.5° (or about half a bin-

ocular field) south of Theta

Leonis to 5th-magnitude 73

Leonis. From there, glance very

carefully about half a field to

the left (east-southeast). Can

you spot a dim smudge of light

there, just south of a faint star?

If so, congratulations — you

just found M66.

Messier’s notes describe M66

as “very weak.” True, it is faint,

but it is certainly well within

the grasp of most binoculars.

My notes made through 10x50

binoculars recall it as an “oval

nebulous disk highlighted by a

brighter central core, which

appears stellar.”

M66 is classified as a type Sb

spiral, with two arms curving

away from the galactic nucleus.

The western arm appears dis-

tended, probably due to a game

of gravitational tug-of-war

waged with a neighboring gal-

axy. There appears to be a large

amount of cosmic dust and

reddish nebulae scattered

throughout M66’s spiral halo,

both signs of extensive star-

formation regions triggered by

intergalactic tidal forces.

When you spot M66, you

may also notice a dimmer oval

smudge of light just to its west.

That’s type Sa spiral M65,

which shows tightly wound

spiral arms in photographs. The

arms appear uniform and

neatly arranged, leading astron-

omers to conclude that M65 is

not the cause of M66’s dishev-

eled appearance.

M65 is about half a magni-

tude fainter than M66, and

therefore more challenging. If

you have trouble, try support-

ing your binoculars on a tripod,

fence post, or by some other

means to steady the view. Like

M66, M65 presents an oval disk

surrounding a starlike core.

Although they appear about the

same length, M65 looks thinner

because of its slightly narrower

tilt from our perspective.

I can see M66 through my

10x50s from my suburban back-

yard fairly routinely, but M65

takes a better-than-average

night. Under superior condi-

tions, however, I’ve spotted both

through braced 7x35 binoculars.

Looking at charts of the area,

you’ll notice a third galaxy just

north of M65 and M66. That’s

NGC 3628. This Sc spiral has

the loosest spiral structure of

the three. From our vantage

point, we see this distant island

universe almost exactly edge-

on. Telescopes show the galaxy’s

edge is girdled by a conspicuous

band of dark dust clouds, which

effectively obscure the bright

central region and hide most of

the young stars in the spiral

arms.

Try as I might, I’ve never been

able to see NGC 3628 through

my 10x50s. It also gives my

16x70s a run for their money.

Only when piloting my 25x100s

can I make out a faint smudge

of grayish light just north of the

other two. It’s a toughie.

Let’s wrap up our survey this

month by visiting a fun bin-

ocular asterism. Follow a zigzag

line south of Theta Leonis, past

the stars Iota (ι) and Sigma (σ)

Leonis, to a small four-star arc

that hooks to the southeast.

The brightest star in the arc,

4th-magnitude Tau (τ) Leonis,

teams with a fainter point to its

southeast to create a pretty

double star through binoculars.

There’s more: By shifting Tau

toward the upper right (north-

west) corner of your field, you

should spot not one, not two,

but three more faint doubles.

All four pairs collectively fall

into an X pattern. Add them

together, and you get an aster-

ism that I like to call the

Double Cross. None of the

four pairs is a true physical

binary since all eight stars are

at very different distances, but

that doesn’t detract from their

unique appearance through our

binoculars.

We all have favorite binocu-

lar objects. I’d enjoy hearing

about yours — contact

me through my website,

philharrington.net.

And always remember that

two eyes are better than one.

The Leo Trio

plus one

Splendid galaxies await

you in the Lion.

Highly inclined spiral M65 is one of the more beautiful galaxies in the springtime sky.

The edge-on galaxy NGC 3628 sports a

dust lane running along its bright disk.

KEN CRAWFORD

Spiral galaxy M66 has a beautiful disk

intertwined with dust lanes and pinkish

star-forming regions. ADAM BLOCK/MOUNT

LEMMON SKYCENTER/UNIVERSITY OF ARIZONA

Phil Harrington is a longtime

contributor to Astronomy and

the author of many books.

ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA