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COMET SEARCH I In the alley of Aries
ALPHONSE BORRELLY’S
DISCOVERY in 1904 came
200 years after Edmond Halley’s
famous prediction that some
comets return. Yet Borrelly’s
comet was only the 19th to
be designated periodic. With
a cycle of 6.86 years, Comet
19P/Borrelly will be back again
in December 2028 with one of
its best apparitions ever.
When it comes to bright-
ness, distance is everything. In
2028, Borrelly will come within
0.41 AU. But our current appari-
tion’s 1.3-AU distance cuts its
shine to 9th to 10th magnitude.
Our advantage this time is
Borrelly’s altitude: It’s halfway
up the southwestern sky as
darkness sets in. Take a look in
Pisces during the first few nights
of February before the Moon
interferes, then jump back at it
in Aries as the dark-sky window
reopens on the 18th.
Away from the city with an
8-inch scope at 150x, we will see
a dense core with a sharply
defined northern edge and a
nicely broad V-shaped fan to
the south. The trailing edge,
where the bigger dust particles
fall behind, will be diffuse. It
will take truly dark skies and
patience to pick it up in a
4-incher, while imagers should
readily capture some classic
green glow. The 5-mile-long,
bowling-pin-shaped nucleus
remains invisible behind the
cloak of dust called the coma.
Comet 19P/Borrelly
–4.9 during the first half of
February. Venus always reaches
its brightest when it’s 26 percent
lit, which occurs Feb. 12.
Typically, Venus is magni-
tude –4.5 at this time, but its
actual brightness also depends
on its distance from Earth. The
reason Venus is exceptionally
bright this month is that its
elliptical orbit carries it closer to
Earth than usual. The typical
variation in distance is between
0.44 and 0.47 astronomical unit
(AU; where 1 AU is the average
Earth-Sun separation) — that’s
40.9 million to 43.7 million
miles. This year, it’s just
0.41 AU (38 million miles),
thus providing one of the rare
moments that the planet
exceeds its usual brilliance.
Follow Venus with a tele-
scope throughout the month.
Situated among the rich star
fields of Sagittarius, you can’t
miss it rising more than two
hours before sunup. The best
times to catch a glimpse are in
late twilight or even daylight.
That’s because the planet’s great
brilliancy causes glare in your
scope when the sky is dark,
making it hard to see well.
On Feb. 1, Venus spans a
giant 49" on the sky but is a
narrow, 16-percent-lit crescent.
During the month, Venus fat-
tens and shrinks in apparent
size. By Feb. 13, it spans 40"
SKY THIS MONTH
Venus reaches an unusually
brilliant moment this month,
when it outshines its normal
greatest brilliancy by a few
percent and hits magnitude
— Continued from page 33
On Feb. 5, Mars comes close to
the globular cluster M22. You can
catch them together in binoculars.
This shot shows a different close
approach, which occurred in
November 2014. ALAN DYER
Comet Borrelly tracks from Pisces into Aries as February progresses,
passing the 9th-magnitude face-on spiral galaxy M74 along the way.
The position of Uranus is shown on Feb. 15.
EVENING SKY
Jupiter (west)
Uranus (southwest)
Neptune (west)
MIDNIGHT
Uranus (west)
MORNING SKY
Mercury (east)
Venus (southeast)
Mars (southeast)
Saturn (east)
WHEN TO
VIEW THE
PLANETS
When Comet 19P/Borrelly returns to the
same region of the sky in December 2028,
astronomers expect it to reach magnitude 8.