AQUILADRACO HERCULESOPHIUCHUSLYRACYGNUSApril 22, 2 A.M.
Looking eastVegaDenebAltairRadiant10°WWW.ASTRONOMY.COM 37RISING MOON I Walled-up perfection
PLATO IMPRESSES THE NEWCOMER as
much as it mesmerizes the experienced seleno-
phile. On the evening of April 1, the large oval is
a striking sight in the northern half of the Moon.
Black shadows painted onto the canvas of its
smooth floor retreat into the eastern wall. Over
the next few hours, the rising Sun in the lunar
sky shortens them even more. The mountains
along the rim are not as sawtooth-shaped as
their shadows imply. You can test this yourself
by stepping outside near sunset and confirming
that your own head isn’t as pointy as its shadow!
As an early-month bonus, look just south of
the equator, where the Straight Wall casts a thin
black shadow almost bisecting a larger crater.
The central peaks that formed during
the birth of Plato lie below the now-solid
surface. Some 3.5 billion years ago, red-
hot molten lava welled up through
cracks but could get no farther than the
tall walls. Since then, a handful of modestly
small impacts have pitted the frozen floor.
With a 6-inch scope and a very steady atmo-
sphere, patient observers can pick out the larg-
est craterlets near the center of Plato.
Return to Plato over the next couple of eve-
nings. A higher Sun better shows off the way the
walls have slumped into the basin. You can repli-
cate this effect at the beach by digging to differ-
ent depths in moist sand and watching the sides
cave in. It’s also neat to compare the texture justover the same period. The
planet reaches greatest bril-
liancy April 27.
There are a few asteroids in
Taurus at the same time. These
include Vesta, which stands
3.7° due north of Gamma (γ)
Tauri (the tip of the Hyades’ V)
on the 7th. At magnitude 8.4,
Vesta is within easy reach of
binoculars. On the 12th, it
comes within 40' of Epsilon (ε)
Tau. E le vent h-ma g n it ude
Metis and 12th-magnitude
Hygiea each lie within 5° of
the Hyades as well.
You’ll have to wait until
nearly 4 a.m. for another planet
to make an appearance in early
April. Jupiter rises at 3:20 a.m.
on April 1, and by 2 a.m. on
April 30. It’s followed soon after
by Saturn and Mars, which
stand 6° farther east and rise
20 minutes after Jupiter on
April 1. The trio of planets
makes a fine sight above the
southeastern horizon in the two
hours before dawn, rising with
the Milky Way. On April 1,
Saturn and Mars are separated
by merely 1°, having passed
their closest the night before.
Let’s take a closer look at
Jupiter first. The giant planet
lies in eastern Sagittarius all
month and brightens from
magnitude –2.1 to –2.3 dur-
ing the month. On April 6,
the much more distant Pluto
stands 45' due south of
Platoinside and outside the large ring — while you
may not be able to resolve the tiniest features,
the smooth crater floor is notably different from
the dappled area beyond the elevated rim.
Have another look on the 30th to see Plato
halfway across the terminator, sporting a bright
rim with a jet-black interior. Closer to moonset
you’ll see light creeping down the western wall
as the Sun rises higher in the lunar sky.— Continued on page 42MARS and SATURN make for a
colorful and contrasting pair in
the early April sky. On April 1,
ruddy Mars is just 1° southeast
of golden Saturn.OBSERVING
HIGHLIGHTMETEOR WATCH I No Moon for April’s best display
CONDITIONS ARE IDEAL for this
year’s Lyrid meteor shower, which is
active between April 14 and 30. The
Moon is almost New when the peak
occurs April 22 in the predawn hours.
The radiant begins in Hercules and
migrates one degree per day, eventu-
ally reaching Lyra; it climbs high after
midnight and is almost overhead in
the hour before dawn.
The expected zenithal hourly rate
is 15 to 20 meteors per hour, which
can be observed on the morning of
peak an hour before twilight begins.
Lower rates occur with the radiant
lower in the sky. Meteors can appear
anywhere in the sky and many are
quite faint, so find a dark location and
watch an area at about 45° altitude,
away from Lyra. The shower has had
some brief elevated rates for short
periods; while none are expected this
year, it’s always worth keeping count.Lyrid meteor showerLY R ID ME TEORS
Active dates: April 14–30
Peak: April 22
Moon at peak: New Moon
Maximum rate at peak:
18 meteors/hourThis 60-mile-wide crater stands between
Mare Frigoris and Mare Imbrium in the
lunar far north. CONSOLIDATED LUNAR ATLAS/UA/LPL;
INSET: NASA/GSFC/ASUWith a New Moon occurring the same day as
this annual shower’s peak, viewing conditions
for the Lyrids couldn’t be better.Mare ImbriumVallis AlpesPlatoMare
FrigorisNE