2019-12-01_Astronomy

SOUTHERN SKY BY MARTIN GEORGE

February 2020

An early morning planet trio

Brilliant Venus con-

tinues to dominate the

western evening sky. It stands

out largely because it shines so

brightly, improving from mag-

nitude –4.1 to –4.3 during the

month. But the lack of any

nearby bright stars enhances its

prominence. The inner planet

leaves Aquarius and enters

Pisces on February 2, moving

eastward across the southern

part of the celestial Fish for the

remainder of the month. Venus

appears fairly low because the

ecliptic — the apparent path of

the Sun and planets across the

sky — makes a shallow angle to

the western horizon after sun-

set at this time of year.

The view of Venus through

a telescope does improve

noticeably in February, how-

ever. The planet’s disk swells

from 15" to 19" across while its

gibbous phase wanes from 74 to

63 percent lit. Even better views

will come a few months from

now when Venus will appear

larger and show a beautiful

crescent phase.

Innermost Mercury also

appears in the evening sky,

though it’s much harder to see.

The planet reaches greatest

elongation February 10, when

it lies 18° east of the Sun. It

climbs only 3° high in the west

a half-hour after sunset, how-

ever, because it also suffers

from the ecliptic’s shallow angle

to the horizon. It will put on a

much better show before dawn

next month.

The rest of the naked-eye

planets reside in the morning

sky. Let the distinctive shape of

Scorpius the Scorpion serve as

a harbinger of the planetary

delights to come. Shortly after

the arachnid rises in early

February, Mars’ ruddy glow

pokes above the horizon.

On February 1, the Red

Planet appears 10° below

Antares, the brightest star in

Scorpius. Like Mars, this red

supergiant star shines at 1st

magnitude and sports an

orange-red hue. The planet

moves away from the Scorpion

during February, traveling east-

ward from neighboring

Ophiuchus into Sagittarius.

Unfortunately, a telescope

doesn’t add much to the view

— Mars shows a featureless

disk just 5" in diameter.

Less than two hours after

Mars rises, Jupiter clears the

horizon. The giant planet

shines at magnitude –1.9, which

makes it some 20 times brighter

than Mars. Jupiter remains in

Sagittarius this month, moving

slowly eastward across the

Archer’s northern section.

The view of Jupiter through

a telescope always impresses.

The gas giant’s disk spans 33"

in mid-February and shows

intricate atmospheric detail.

And even the smallest instru-

ment reveals the planet’s four

bright moons, which change

relative positions noticeably

from night to night.

You don’t even have to wait

an hour after Jupiter first

appears to see magnitude 0.6

Saturn glowing softly to its

lower right. The ringed planet

also resides in Sagittarius, near

that constellation’s eastern bor-

der with Capricornus. Saturn

looks magnificent through any

telescope, though the view

improves later in the month as

it climbs higher before dawn.

On the 29th, the planet’s disk

measures 15" across while its

lovely rings span 35" and tilt

22° to our line of sight.

The starry sky

Few sights in the southern sky

attract more attention than the

Magellanic Clouds. These two

nearby galaxies — satellite sys-

tems to our Milky Way —

stand out to the naked eye

under a dark sky. They are cir-

cumpolar objects, meaning

they never set, from latitudes

south of about 25° south. You

can find both high in the

southern sky on February eve-

nings, looking like detached

pieces of the Milky Way.

The most famous sight

within these galaxies is the

Ta r a nt u la Nebu la (NG C 2 070)

in the Large Magellanic Cloud

(LMC). This vast star-forming

region is the largest known in

our part of the universe, and it

glows brightly enough to show

up without optical aid across

160,000 light-years of interven-

ing space. It appears so won-

derful, in fact, that it’s easy to

forget the LMC’s many other

attractive sights.

This month, let’s look at a

fascinating group of open star

clusters: NGC 2164, NGC 2156,

NGC 2159, and NGC 2172. The

four clusters form a tight col-

lection some 0.3° across located

near the LMC’s eastern extrem-

ity. Look for them about 1°

west-northwest of the 5th-

magnitude star Nu (ν) Doradus

(which belongs to the Milky

Way). If you have a go-to

mount, center on right ascen-

sion 5h58m and declination

–68°35' (2000.0 coordinates).

The clusters form a shape

like a capital letter T, with the

horizontal bar of the T signifi-

cantly longer than the vertical

one. To see them well, use a

20-centimeter or larger scope.

Initially, all four will appear as

slightly fuzzy stars; NGC 2164

is the easiest to spot while

NGC 2172 is the most difficult.

Don’t forget, you’re viewing

open clusters in another galaxy.

Despite their great distance,

NGC 2164 shows a slightly

mottled appearance at moder-

ately high magnification. In

fact, I can partly resolve this

cluster through my 20-cm

Schmidt-Cassegrain telescope

at a magnification of 222x. The

cluster appears beautiful with

averted vision. This time-tested

technique, in which you look

slightly to the side of your tar-

get to use your eyes’ more light-

sensitive rods, helps you to pick

up fainter details.

A close inspection of the

three fainter clusters with the

same telescope-eyepiece combi-

nation shows that they all can

be partially resolved, though

with greater difficulty than

NGC 2164. Of these other

three, I find NGC 2159 to be

the easiest.