Astronomy - USA (2020-01)

January 4, 4 A.M.

Looking east-northeast

DRACO

URSA MINOR

URSA MAJOR

BOÖTES

CORONA

BOREALIS

HERCULES

Radiant

Vega

Arcturus

10°

N

E

WWW.ASTRONOMY.COM 37

RISING MOON I Fabulous Fracastorius finds the spotlight

THERE’S MORE TO LUNAR HISTORY than

younger craters erasing older features. For

example, the massive impact that carved out

Mare Nectaris (Sea of Nectar) affected the face

of cratering for millions of years. The Sun nicely

illuminates Mare Nectaris on January 1. Three

intriguing craters on the sea’s western side

immediately catch the eye, as does the bright

white arc of Rupes Altai. Perfectly centered on

Nectaris, the arc is a remaining section of the

fourth rim of this multiring basin.

The younger crater Piccolomini dangles on

the southern end of Rupes Altai like a hoop

earring. Spanning 55 miles, Piccolomini is

big enough that it sports a complex of

central peaks instead of a single one like

those seen in the many smaller pock-

marks that pepper the surroundings. Also

check out its walls. Similar to a hole dug in

wet sand at the beach, lots of material

slumped into Piccolomini’s cavity. The crater’s

southern side has more thanks to the unstable

terrain generated when Rupes Altai formed.

The broken circle of the 75-mile-wide crater

Fracastorius is intermediate in age between

Nectaris and Piccolomini. Just as water finds its

level, so does lava, which makes it clear that

Fracastorius tilts down to the north. Lunar geol-

ogists have deduced that before the final flood

in this region, a smaller surge of lava rose up

through cracks in Nectaris’ floor, solidified,

and depressed the central part. This caused

This lovely sea and flooded crater take

center stage on the waxing crescent Moon

on January 1 and 30. CO NSO LI DATED LU NAR ATL A S/

UA/LPL. INSET: NASA/GSFC/ASU

in the inner solar system, closer
to the Sun than Earth, and lies
104 million miles from us at
the time of the conjunction.
Neptune is the solar system’s
most distant major planet and
stands 2.85 billion miles away.
These distances dramatically
affect what you see through a
telescope. Despite having a
physical diameter four times
larger than Venus, Neptune
appears only 2.2" across while
Venus spans 15".
Neptune’s appearance
remains rock steady throughout
January, but Venus shows subtle
changes to a discerning eye.
On January 1, the inner planet’s
disk measures 13.1" across and
appears 82 percent lit. By the
31st, Venus spans 15.3" and the
Sun illuminates 74 percent of its
Earth-facing hemisphere. (The
disk looks sharper if you view it
in twilight, avoiding the intense
glare between a bright planet
and the dark sky.) Consider
making a pencil sketch of the
disk in your observing note-
book every couple of weeks. If
you keep this up through the
end of the current evening
apparition in May, you’ll have a
nice record of the planet’s grow-
ing size and waning phase.
While you’re waiting for the
sky to darken and Neptune to
emerge, lower your gaze toward
the horizon. That’s where you’ll
find Mercury during the last
week of January. Your first

Mare Nectaris and Fracastorius

the surrounding terrain to tilt down toward

the sea’s center. By the way, Fracastorius did

not get its name because it is fractured; instead,

it honors the 16th-century Italian astronomer,

physician, and poet Girolamo Fracastoro.

If you miss viewing the Moon on New Years’

Day, similar lighting returns January 30. Watch

the peaks of Rupes Altai and Piccolomini pop

into view one by one as the evening progresses.

With the Sun rising slowly over this rugged lunar

terrain, high points to the west and lower points

to the east light up with each passing half-hour.

— Continued on page 42

When VENUS slides past

NEPTUNE in late January, the

two planets come closer than

they have in 36 years.

OBSERVING

HIGHLIGHT

METEOR WATCH I A short but dynamic shower

THE YEAR’S FIRST METEOR

SHOWER not only ranks among

the best, but also among the least

observed. Although the Quadrantids

can produce up to 120 meteors per

hour, January’s cold and often cloudy

weather discourages viewers. The

shower also has a sharp maximum,

and meteor numbers remain above

half the peak level for only four hours.

This year, however, conditions

look great. The Quadrantids peak

before dawn January 4 from North

America, and the slightly gibbous

Moon sets around 1 A.M. local time. If

the sky cooperates, observers should

be in for a great show. The meteors

appear to radiate from northern

Boötes — an area once occupied by

the now-defunct constellation

Quadrans Muralis — a region that

climbs highest just before dawn.

Quadrantid meteor shower

January meteor viewing reaches

its peak with the perfectly timed

Quadrantids, which could deliver

up to two meteors per minute.

QUADRANTID METEORS

Active dates: Dec. 28–Jan. 12

Peak: January 4

Moon at peak: Waxing gibbous

Maximum rate at peak:

120 meteors/hour

Mare Nectaris

Fracastorius

Piccolomini

Rupes Altai