April 9, 1 hour before sunrise
Looking southeastJupiterMars SaturnAltairSAGITTARIUS
CAPRICORNUSAQUARIUSAQUILA10°1°ENMay 1 Path of Vesta(^2621)
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NGC 1647 April 1
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WWW.ASTRONOMY.COM 43
LOCATING ASTEROIDS I
Keep trucking through Taurus
THE THIRD-LARGEST OBJECT in the asteroid belt, 4 Vesta,
passes Aldebaran, the ruddy eye of the celestial Bull, this month.
That meeting makes it fairly easy to swing your scope to the
right place. At 300 miles across, the potato-shaped minor planet
glows at magnitude 8.5; it will require some patience and a
4-inch scope from the suburbs to pick it up. As Vesta approaches
the Milky Way, the background stars become more numerous,
making following it a bit like tracking a person disappearing into
a crowd.
Helping us distinguish Vesta are dust lanes that block out the
real profusion of stars in this section of the Perseus spiral arm of
our galaxy. The surefire way of confirming which dot is Vesta and
which is a star is to make a quick sketch one night, then come
back on a following one to see which has moved. There really
isn’t enough time in one evening to catch its shift against the
background before it sets.
From April 11–13, Vesta sits a bit more than 30' north of Epsilon
(ε) Tauri. That’s the apparent diameter of the Moon. If you see a
star right on the indicated path, you’ve got it! While you are in the
region, check out the open star cluster NGC 1647. It contains a few
dozen stars ranging from 8th to 11th magnitude. Select an eye-
piece that shows a bit more than the whole Moon and wait for
your eyes to dark adapt to see the fainter ones popping in.
The Moon is but a thin crescent when Vesta passes by, so it
will not interfere with our observation of the asteroid this month.
Vesta zips past the Hyades
midmonth is 37" and the
minor axis is 13", while the
disk spans 16". This means the
northern pole of Saturn covers
the far side of the rings. Note
the shadow of the planet fall-
ing on their far western side.
Saturn is accompanied by a
variety of moons, the brightest
of which is Titan, shining at
8th magnitude. It’s likely the
only one you will see in early
April, since Saturn is only
about 15° high at the onset of
twilight. The fainter moons
may have to wait until later in
the month, when the planet
reaches 25° by 5 a.m. local day-
light time. Smaller moons like
Tethys, Dione, and Rhea shine
between 10th and 11th magni-
tude, and orbit much closer to
Saturn than Titan.
Mars begins the month of
April 1° southeast of Saturn
and shines at magnitude 0.8.
The striking color contrast
between these two planets is
evident to most eyes with good
night vision. Rust-colored
Mars is distinctly different
from the soft yellowish glow
of Saturn.
Mars is the next planet
beyond Earth’s orbit and conse-
quently moves quickly com-
pared with the more sedentary
ringed planet. Its higher velocity
carries Mars quickly eastward
relative to Saturn’s location;
during April, the Red Planet
crosses most of Capricornus,
ending the month 2.7° due west
of Deneb Algedi, a 3rd-magni-
tude star in the constellation’s
northeast region.
By April 30, Mars brightens
to magnitude 0.4 and is begin-
ning to grow in apparent size,
albeit slowly. Opposition is not
until October, but already
Mars spans more than 7" and
soon will begin to show off
surface detail to smaller
scopes. Right now, it’s small
in a 14-inch scope.
Mercury shines at magni-
tude 0.0 on April 1 and you
can catch it 3° high in the east-
ern sky 30 minutes before sun-
rise. On April 3, Mercury is
1.5° south of Neptune, which
lies in the far distance and is
too faint to see in twilight.
Mercury brightens to magni-
tude –0.2 by April 10, but the
increasing brilliance is coun-
tered by its elevation dropping
slightly lower each morning at
the same time before sunrise.
See how far you can follow this
elusive planet before it suc-
cumbs to twilight.
Uranus and Neptune are
both on the far side of the solar
system. You may catch a glimpse
of Uranus just after sunset in
A triple delight before dawn
GET DAILY UPDATES ON YOUR NIGHT SKY AT
http://www.Astronomy.com/skythisweek.
early April, or sneak a peek of
Neptune not long before sunrise
late in the month.
Martin Ratcliffe provides
planetarium development for
Sky-Skan, Inc., from his home
in Wichita, Kansas. Alister
Ling, who lives in Edmonton,
Alberta, has watched the skies
since 1975.
The three bright morning planets spread out a bit in April, with Saturn
perching midway between Jupiter and Mars on the 9th.
This 8th-magnitude asteroid glides north of the V-shaped Hyades star cluster
and 1st-magnitude Aldebaran during April.