Sky & Telescope - July 2019 - 27

LE AH TISCIONE / S&T

distance north of the Apollo 11 landing site and due east of
the Ritter and Sabine crater pair. Armstrong, the largest, is
4.2 km across followed by Aldrin at 3.4 km, and Collins at 2.4
km. A 6-inch scope at 250× on a night of steady seeing should
coax all three into view. (6 days after new)
15 Serpentine Ridge - This snaking, low-elevation ridge
in Mare Serenitatis formed when the lava inside the basin
cooled. As it settled, it fractured, sending pieces of hardened
rock sliding over one another to create long ropes of debris.
(6-7 days after new)
16 Triesnecker and Ariadaeus Rilles - Two of the
Moon's most prominent rille systems formed from faulting of
the crust. The Triesnecker complex is so rich in chasms that
it looks like a spider web at high power on nights of good seeing. Spectacular! (7-8 days after new)
Southern Highlands - This craterscape, which includes
Tycho and Clavius, is crater heaven. Thousands of overlapping craters greet the eye, a forceful reminder of the Moon's
impactful history. Tycho, with its sharp rim and point-like
central peak (a stunner at lunar sunrise), is one of the
Moon's largest and youngest craters, with an estimated age
of 108 million years. (Most lunar craters are a few hundred
million to a few billion years old.) Nearby Clavius (231 km)
hosts its own crater farm, a scenic arc of ﬁve sizable impact
holes contained within its rim. (6-9 days after new)
17 Rupes Recta - Commonly known as the Straight
Wall, this 300-meter-high, 116-km-long cliff, which runs
along the eastern edge of Mare Nubium, is the Moon's most
prominent geologic fault. The delicate rille Rima Birt just to
its west is also worth a visit. (8 days after new)
10 Plato (101 km) - It looks like a swimming pool, but
don't dive in or you'll hurt your head. At ﬁrst glance, the crater's ﬂoor appears perfectly smooth, but crank up the power
to see if you can spot the craterlets - "easy" ones are about
3 km across - that make it wonderfully imperfect. (8-9 days
after new)
5 Montes Apenninus - The lunar version of the Apennine Mountains forms a prominent arc of rugged peaks with
elevations of 2-5 km. While tectonic forces drive the formation of mountains on Earth, the Moon's Apennines formed
3.9 billion years ago from material pushed up during the
giant impact that created nearby Mare Imbrium. (8-9 days
after new)
1 Copernicus (93 km) - A most wonderful crater!
Catch it around sunrise when its sunlit rim frames a bowl
of darkness. With terraced walls and multiple central peaks,
this crater will keep you glued to the eyepiece. Chains of
secondary craters, visible at high magniﬁcation, perforate the
landscape in all directions. (9 days after new)
12 Sinus Iridum (249 km) - An enormous, mare-ﬁlled
impact crater along the northwestern edge of Mare Imbrium.
At sunrise, ridges of lava look like waves on a sea. (10 days
after new)
18 Milichius Pi (π) (10 km) and 19 Marius Hills (6-16
km) These are great examples of lunar domes, a type of shield

volcano similar to those found on Earth. You can even spot
the craterlet at the summit of the Milichius dome at 150×
or higher in good conditions. The Marius dome ﬁeld lies
immediately west of the crater Marius. The region is "warty"
with rough-textured domes. (10 days and 12 days after new,
respectively)
20 Gassendi (110 km) - This crater's fractured ﬂoor is
riddled with rilles and partially ﬂooded by lava via a breach in
its north wall. (10-11 days after new)
2 Aristarchus and Aristarchus Plateau (40 km)
- Shining at full Moon like a 1,000-watt LED light at the
center of prominent rays, Aristarchus is the brightest of the
larger lunar craters. The crater dominates a pale green-yellowcolored volcanic plateau. (12 days after new)
21 Schickard (227 km) - The ﬂoor of this giant crater
near the Moon's southwestern limb is covered with material
ejected from the nearby Mare Orientale impact, giving it a
two-toned appearance. (12-13 days after new)
22 Mare Orientale - At 3.85 billion years old, this is the
Moon's most recent impact basin. Due to extreme foreshortening at the western limb, Mare Orientale looks like a series
of vaguely concentric stripes of dark lava separated by lighter
highland material. (Full Moon to 3 days before new, when a
favorable libration exposes the western limb).

¢ Contributing Editor BOB KING has been an avid observer
since childhood. He's a long-time member of the American
Association of Variable Star Observers and author of several
observing guides, including Night Sky with the Naked Eye
and Wonders of the Night Sky. Visit his website at astrobob.
areavoices.com.

A Little Help
Here are a few books and tools to make it
easier to visit the Moon, our closest planetary
companion.
Charles Wood and Maurice
Collins, 21st Century Atlas
of the Moon (West Virginia
University Press, 2002). This
atlas features high-quality
photomaps and detailed
descriptions of features.
Antonin Rükl, Atlas of the
Moon (Sky Publishing, 2007).
Rükl's is the current "bible"
of lunar atlases, but it's only
available on the used market.
LROC Quickmap (quickmap.
lroc.asu.edu). This fantastic
online Moon browser is based
on images from NASA's Lunar
Reconnaissance Orbiter
Camera.

Virtual Moon Atlas (ap-i.net/
avl/fr/start). Use this handy,
free desktop atlas to plan your
next lunar observing session.
Moon Globe (https://is.gd/
MoonGlobeApp). This easyto-use, free Moon atlas works
on iPhones and iPads.
Moon Atlas 3D (https://is.gd/
MoonAtlasApp). Download
this lunar atlas app for your
Android phone.

http://astrobob.areavoices.com http://astrobob.areavoices.com http://www.ap-i.net/avl/fr/start http://www.ap-i.net/avl/fr/start https://www.is.gd/MoonGlobeApp https://www.is.gd/MoonGlobeApp https://www.is.gd/MoonAtlasApp https://www.is.gd/MoonAtlasApp http://quickmap.lroc.asu.edu http://quickmap.lroc.asu.edu

Sky & Telescope - July 2019

Table of Contents for the Digital Edition of Sky & Telescope - July 2019