Skywatch - 2021 - 70

Beginner's Guide
The next total lunar eclipse happens
on May 26th and favors the Pacific,
Australia, and Antarctica. More exciting for North American skywatchers is
the partial eclipse of November 19th.
This event is very nearly total - only
a razor-thin sliver of the Moon will lie
outside the Earth's dark umbral shadow.
(Details can be found on page 50.)
While you can easily follow the progress of a lunar eclipse with your eyes
alone, as with so many sky sights, binoculars can really enhance the experience.

70 SK Y WATCH 2021

S Seven

sisters The Pleiades star cluster in the winter constellation Taurus is one of the binocular
sky's ﬁnest sights.

The Moon in Binoculars
Earth's companion dominates the night
sky for nearly half of every month.
Indeed, the very word "month" comes
from the Germanic and Old English
name for the interval between one full
Moon and the next, a period of around
29½ days. The surface of the Moon
is transformed in binoculars, but to
make the most of the view, it really pays
to steady your binoculars by leaning
against a low fence or wall, or better yet,
by mounting them on a camera tripod
via a specialized adapter.
The most obvious features of the
Moon are the large dark areas. Before
the invention of the telescope, astronomers believed the dark regions to be
seas, or maria in Latin (singular, mare). If
Earth has oceans, why not the Moon,
right? Sadly, the lunar surface is bonedry. But the maria were once vast pools
of molten lava that oozed to the surface
from the Moon's interior, flooding the
lunar lowlands 3 to 4 billion years ago.
Binoculars will also reveal innumerable overlapping saucer-shaped craters.
They vary in size from small pits at the
threshold of vision up to around 250 km
in diameter. Some feature distinct central mountain peaks. All the craters you
can see in your binoculars were formed
by powerful impacts - space rocks and
comets slamming into the lunar surface.
The Moon also has mountains, but
unlike those here on Earth, the lunar
mountain ranges are the remnants of
rims from the most powerful impacts
of all - those that formed giant lunar

basins. The Moon's peaks soar to
heights of several kilometers above the
surrounding plains.
While you might expect that full
Moon would be the ideal time to inspect
the lunar surface, that's not the case.
When the Moon is full, the Sun's rays
fall vertically on the lunar surface,
which means craters and mountains
lack shadows, making these features difficult to discern. Instead, at any other
time you'll see the greatest detail in a
zone near the terminator - the line that
divides night from day on the Moon.
There, craters and other features are
thrown into stark relief.
However, full Moon is a good time
to observe the dark maria and the long,
bright rays surrounding some larger
craters. Especially prominent are the
rays radiating from Tycho and Copernicus. Tycho's rays are so extensive that
they give the Moon the appearance of a
peeled orange.
Going Deeper
Binoculars are also excellent for viewing bright comets. Although truly bright
comets are quite rare, one comes along
every decade or so on average.
Comets are often described as "dirty
snowballs" that originate from the
cold, distant outer reaches of the solar
system. When they visit the inner solar
system, they can sprout impressively
long, beautiful tails. Although the most
spectacular comets, like 2020's Comet
NEOWISE, grab all the headlines, binoculars allow you to see the much more

GARY SERONIK

Binocular Observing
Sooner or later you'll be keen to augment your views of the night sky with
some sort of optical aid, and the best
and most cost-eﬀective way to do that is
with binoculars. They're portable, easy
to use, and ready at a moment's notice.
Plus, they can perform double duty for
daytime leisure activities, such as birding. Best of all, there's a good chance
you already have a pair.
Binoculars' objectives (their front
lenses) gather far more light than our
eyes do alone, permitting us to see
much fainter stars. Their magnification enables us to see objects in greater
detail. Binoculars labeled, say, 10×50,
means that the instrument has a magnification power of ten times (10×) and
objective lenses 50 mm (2 inches) in
diameter. Binoculars that magnify 10×
are about the maximum that can be
handheld without the image shaking too
much. Many observers favor 10×50s or
7×50s - I fi nd that 8×40s are a nice
compromise between weight, aperture,
and magnification.
Another important consideration is
a binocular's field of view - the size of
the circle of sky visible through it. For
typical 10× binos, this is about 5°. While
that's large enough to easily locate
the Moon or bright planets, it takes
a little practice to instinctively raise
your binoculars to the correct spot for
other objects. However, this skill soon
becomes second nature. Knowing your
binocular's field of view permits you to
star-hop to faint targets with the aid
of a star chart (as described in the box
on page 72).

Skywatch - 2021

Table of Contents for the Digital Edition of Skywatch - 2021