2°April 1^5101520
25
30EN51LEO
DenebolaChertanZosma^60fPath of VestaM95M96M105
M66NGC 3628M6510°April 6, 1 hour before sunrise
Looking southeastAQUARIUS SAGITTARIUS
CAPRICORNUS
SaturnJupiterDeneb
AlgediAltairMoonAQUILA
WWW.ASTRONOMY.COM 39
LOCATING ASTEROIDS I
A walk in the park
SIMPLE, RELAXING ASTEROID TRACKING like this happens
only every three years or so. This month, asteroid 4 Vesta shines
at magnitude 6.6, easy pickings with binoculars from the city. Its
background constellation of Leo is recognizable from light pol-
luted areas, with the blue-white luminary Regulus leading it high
in the southeast. Combine this with mild spring evenings and it
rarely gets better for asteroid watchers.
After two or three sightings, you won’t even need a chart to
find it. For the first search, though, use our chart to guide you
to the spot near Leo’s hindquarters, notable for its perfect
right-angled triangle. In a logbook or on a blank sheet or paper,
place the brightest six dots with a pencil. Create a large version
so you have enough room to add Vesta’s slow shift every three
or four nights.
A typical amateur won’t be able to detect Vesta moving dur-
ing one observing session this month because it appears to slow
down and turn in a tight curve. Earth passed it by on our faster
inside track, causing this part of a retrograde loop. The bright
light of the waxing gibbous Moon on the 21st through the 23rd
interferes, so give these nights a pass.
Spanning 310 miles (499 km), Vesta is a large object in the
main asteroid belt, second only to dwarf planet 1 Ceres.planet — a result of the vary- Making the turn (^)
ing albedo (reflectivity) of its
surface. Saturn’s low altitude
creates another challenge here.
However, on April 16, Iapetus
reaches its brightest western
elongation, presenting a good
opportunity to identify it with
small telescopes. Iapetus lies
8' due east of Saturn, so use
a low-power eyepiece with a
field of view of at least 1/3°
to search for the moon.
Jupiter rises 35 minutes
after Saturn in early April,
shortly before 5 A.M. local time.
It lies in the northeastern part
of Capricornus. On April 7, it
stands 2° due north of Deneb
Algedi (Delta [δ] Capricorni).
Jupiter brightens by 0.1
magnitude to –2.2 during the
month and treks eastward,
crossing into Aquarius on
April 25.
The best telescopic views are
later in the month, when the
giant planet has time to rise
higher in the sky. It reaches 18°
in elevation in the southeastern
sky by 5 A.M. local time on
April 30, just as dawn begins to
break — a great time to check
out atmospheric features on the
37"-wide disk. Its four Galilean
moons wander around the
planet in various intervals, and
their changing positions are
fascinating to track.
As Jupiter rises on April 9,
Io is already transiting the disk.
The moon is preceded by its
dark shadow, farther west on
the planet’s face. Io’s shadow
slips off the disk at 6:28 A.M.^
EDT, visible in darkness across
the U.S. But only those in west-
ern locations will be able to
watch Io make its way off the
western edge of the disk an
hour later. There are many
more transits and occultations
throughout the month.
Between now and August,
when Jupiter reaches opposi-
tion, the gas giant will climb
higher in the eastern sky each
month, gaining altitude and
offering improved conditions
for observing.
Neptune rises at the break
of twilight at the end of April,
having passed through superior
conjunction in March.
By 5:30 A.M. local time, the
planet stands 10° high in the
eastern sky, nearly 5° east of
4th-magnitude Phi (φ) Aquarii.
Neptune is dim at magnitude
7.8; if you’re lucky, you can
catch it before the sky bright-
ens. Its visibility will improve
through the summer.
The Moon joins Jupiter and Saturn (^)
Uranus is in conjunction
with the Sun April 30 and only
brief ly visible low in the eve-
ning sky early in the month.
GET DAILY UPDATES ON YOUR NIGHT SKY AT
http://www.Astronomy.com/skythisweek.Martin Ratcliffe is a
planetarium professional and
enjoys observing from Wichita,
Kansas. Alister Ling, who
lives in Edmonton, Alberta, is a
longtime watcher of the skies.Asteroid Vesta is easy to spot this month as it makes a quick turnaround
in Leo the Lion.Giant planets Jupiter and Saturn rise before the Sun this month. On April 6,
a waning crescent Moon joins the pair in Capricornus.