Astronomy

RISINGMOON
Poking through Imbrium’s thick shell
Lambert and Mons La Hire
When scientists talk about youthful
features on the Moon, don’t
think these landscapes are actually
young. For example, the
great floods of molten lava that
filled the giant Imbrium impact
basin ended about 3 billion years
ago. We know that the frenetic
bombardment of the inner solar
system had quieted down before
that, otherwise the lava plains
would contain nearly as many
craters as other regions do.
An evening after June 12’s
First Quarter Moon, the impact
crater Timocharis stands out atop
Imbrium’s plains north of the
lunar equator. And on the 14th,
the 19-mile-wide Lambert Crater
comes into view, casting a long
shadow into Luna’s nightside.
Look carefully just south of this
crater and you should see the
ghostly ring of Lambert R. Scientists
suspect that this circular feature
is an old crater buried by
lava whose peaks barely deform
the surface. The gentle slopes
show up only at low Sun angles.
The isolated peak of Mons La
Hire peeks out of the darkness
June 14, catching the Sun’s rays
one night before the base experiences
sunrise. Lunar scientists
William Hartmann and Charles
Wood proposed in 1971 that this
mountain shares a history with
Mons Pico and Mons Piton on
N
Mare Imbrium’s northern side.
Giant impacts typically create
multiple-ring structures, and this
trio of towers marks Imbrium’s
tallest ring. Lava buried the rest
of this quasi-circular chain, but
E
Mons La Hire
Lambert
The waxing gibbous Moon features distinctive Lambert Crater and the
isolated peak Mons La Hire. CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU
like Lambert R, it deforms the
surface into ridges. One such
segment appears northwest of
Lambert. This, too, will disappear
under a higher Sun, so don’t wait
to look for it.
8th-magnitude globular star
cluster NGC 5897. By then
Mars has faded to a stillbrilliant
magnitude –1.4.
The planet’s dimming
reflects its motion away from
Earth, so it should come as
no surprise that the world
appears to shrink. When
viewed through a telescope
June 1, Mars spans 18.6",
the same as it was at closest
approach May 30. By the end
of June, the planet’s diameter
has dwindled to 16.5". Still,
that’s plenty big enough to
show major features through
small instruments, particularly
when Mars climbs highest
around midnight.
The one feature visible
throughout the month is the
north polar cap, which appears
as a white region on the planet’s
northern limb. Mars’ axis
tilts about 15° toward Earth in
June, keeping the north pole
on constant display. After the
ice cap, the two most conspicuous
features are the dark
OBSERVING
HIGHLIGHT
METEORWATCH
Sporadic meteors
on the prowl
The short nights around the summer
solstice are bereft of any
major meteor shower, but at least
the warm weather makes for comfortable
viewing. Although several
minor showers populate these
June nights, none generates more
than a couple of “shooting stars”
per hour. You’re more likely to
spot a random bit of solar system
debris getting incinerated in
Earth’s upper atmosphere.
The best time to view these socalled
sporadic meteors is in the
early morning. We then lie on the
part of Earth facing in the direction
of its orbital motion, and particles
region Syrtis Major and the
bright Hellas basin. Conveniently,
Hellas lies due south
of Syrtis Major. From North
America, both appear near
Saturn reaches its 2016 peak on June 2/3, shining at magnitude
0.0 and appearing 18.4" across through a telescope.
Catch a sporadic meteor
Bright fireballs occasionally erupt from the larger chunks of solar system
debris that randomly strike Earth’s upper atmosphere. MANOJ KESAVAN
striking the atmosphere tend to
shine brighter than those hitting
Earth’s trailing side (before
midnight). The Moon stays out
Mars’ central meridian around
midnight local daylight time during
June’s final week.
Next up is Saturn, which
reaches opposition the night of
of the morning sky during the
first half of June, so keep watch
for a bright rogue meteor as
dawn approaches.
June 2/3 among the background
stars of southern
Ophiuchus. The ringed
planet then lies low in the
southeast after sunset and
remains visible all night.
It peaks some 30° above
— Continued on page 42
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