2019-04-01_Astronomy

BINOCULARUNIVERSE

BY PHIL HARRINGTON

64 ASTRONOMY • APRIL 2019

E

xcept for Ursa Major,

Leo the Lion is the

most easily recogniz-

able constellation of

the northern spring

sky. Brilliant Regulus, the

Lion’s heart, first draws our

attention to the celestial king of

the beasts. His head and body

are framed by a distinctive

curve of stars resembling a

backward question mark or

a farmer’s sickle, and a large

triangle of stars to its east.

Regulus [A lpha (α) Leonis]

marks the handle end of the

Sickle asterism. Nicolas

Copernicus is credited with

naming this star Regulus, mean-

ing “Little King” in Latin,

although he was not the first to

refer to it as kingly. Many

ancient cultures — including the

Arabians, Babylonians, and the

Akkadians of Mesopotamia —

also viewed it as celestial royalty.

Regulus is a quadruple-star

system. The bright star we see is

a blue-white, spectral type B

main sequence star, orbited by a

white dwarf companion that has

never been observed directly.

Through binoculars, however,

we can see the system’s third

member, an 8th-magnitude

point nearly 3' from the brilliant

primary sun if the latter is

moved out of the field. This star

is itself a binary system, but see-

ing its companion is restricted

to large amateur telescopes.

Next, try your luck with

R Leonis, a long-period, red

giant variable star that’s perfect

for binoculars. The American

Association of Variable Star

Observers (AAVSO) says that

R Leonis is the most widely

observed variable in the

northern spring sky.

One reason for that is its

location, only about 6° west of

Regulus and just south of 19

Leonis. Over the course of 312

days, R Leonis f luctuates from

magnitude 5.8 to 10.0, and back

again. That’s bright enough to

watch through most binoculars

across its full cycle.

It’s fun to trace the changes

in brightness over several weeks

and months. By comparing its

brightness to that of nearby

stars that don’t vary, you can

create your own light curve,

which plots the changes in

brightness over time. To do

that, you’ll need an accurate

chart of the area. You can create

your own using the AAVSO’s

online Variable Star Plotter at

http://www.aavso.org/apps/vsp.

Right now, R Leonis is on a

downward slide, having reached

peak brightness in February.

But thanks to its bright range

and strong reddish glow, R

Leonis is sure to become one of

your seasonal favorites. R Leo

will remain visible in the eve-

ning until early June and then

return to the early morning sky

by mid-September.

The barred spiral galaxy

NGC 2903 is one of the bright-

est and largest galaxies in the

spring sky. Yet Messier and his

contemporaries missed it, even

though it would have been vis-

ible in their telescopes. Instead,

its discovery was left to William

Herschel, who first spotted it

November 16, 1784.

To find NGC 2903, trace the

Sickle to Epsilon (ε) Leonis at

the “tip,” and then glance west

with your binoculars to 4th-

magnitude Lambda (λ) Leonis.

Centering on Lambda, shift

your attention 1.5°, or about a

quarter of a field, due south.

Can you make out a faint oval

disk of grayish light highlighted

by a brighter central core?

That’s the galaxy.

When we look toward

NGC 2903, we are seeing a near

twin of the Milky Way from 20

million light-years away. Both

galaxies show pronounced bars

extending from their central

cores, with gently wrapping

arms curving away from the

ends. The arms of NGC 2903,

invisible through binoculars

owing to their faintness, curve

more casually than those of our

Milky Way.

Finally this month, we leave

Leo behind and head north to

his little brother, Leo Minor.

While there isn’t much to see

here by eye or binoculars, we do

have one port of call that makes

a fun diversion. In 1988, Ohio

amateur astronomer Dan

Hudak wrote a letter that

appeared in that summer’s issue

of Deep Sky magazine, describ-

ing an asterism measuring

about half a degree across that

looked like a celestial sailboat.

Although he found the Sailboat

using a telescope, it’s also faintly

visible through binoculars.

Begin at Mu (μ) Leonis, the

northern point of Leo’s Sickle.

Scan northeastward for 7°,

crossing Leo and Leo Minor’s

shared border, until you arrive

at 6th-magnitude 22 Leonis

Minoris. That star marks the

boat’s bow. Four 7th- and 8th-

magnitude stars in a trapezoid

west of 22 LMi outline the deck

and hull, while 8th-magnitude

SAO 61926 marks the stern.

The tall mast is formed by

three stars, ending at SAO

61951. Be aware that through
       binoculars, the Sailboat seems
       to have capsized, as its mast
       points toward the south.
       I’d enjoy hearing about
       your favorite binocular objects,
       and possibly featuring them
       in future columns. Contact
       me through my website,
       philharrington.net. Until next
       month, remember that two
       eyes are better than one.

Into the Lion’s den

Check out these bright treasures of the constellation Leo.

Regulus, the brightest star in Leo, is an intensely luminous blue-white B-type star that

hides a multiple system orbiting around it. JOHN CHUMACK

The beautiful spiral galaxy NGC 2903 in Leo is visible in binoculars as an oval smear of

light, its photons having traveled 20 million light-years across intergalactic space.

Phil Harrington is a longtime

contributor to Astronomy and

the author of many books.

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