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BirtNicolletArzachelArzachel52 ASTRONOMY • APRIL 2021
Here’s a strategy that will help you enjoy
our closest celestial neighbor. BY MICHAEL E. BAKICH
Easy Moon observing
IF YOU LIVE IN or near a large, well-
lit city, or own only a small telescope,
your observing choices are limited. One
object that won’t disappoint you, how-
ever, is the Moon. Following it telescopi-
cally through a lunar month can be fasci-
nating. But keep in mind that, as opposed
to every other celestial body, the brightest
Moon is the worst time to view it. That’s
because the Sun is shining on the Moon
from directly behind us, which shrinks
shadows and hides details.
Two intervals during the lunar
“month” (from one New Moon to the
next) are best for observers. The first
begins shortly after New Moon and con-
tinues until two days past First Quarter.
Amateur astronomers tend to favor this
span because the Moon lies in the eve-
ning sky. An equally good observing
period starts about two days before Last
Quarter and goes until the Moon lies soclose to the Sun that it’s lost in morning
twilight. During each of these spans,
shadows are longer and features stand
out in sharp relief. One benefit you’ll get
if you observe the Last Quarter Moon is
that the atmosphere before dawn is
steadier than after sunset, when a lot of
heat remains in the atmosphere.Strategy
The best places to point your
telescope lie along the termi-
nator, the line that divides the
Moon’s light and dark portions.
Here you can spot the tops of
mountains protruding just high enough
to catch sunlight, while the surround-
ing lower terrain remains in shadow. On
large crater f loors, you can follow “wall
shadows” cast by the towering sides of
those craters. Features along the termi-
nator change in real time and, during a
night’s observing, the differences you’ll
see through your telescope are striking.
Observing on successive nights makes iteasier to follow the terminator’s progress.
By far the greatest percentage of lunar
features are craters. Craters range in size,
so challenge yourself by finding the
smallest crater you can see. Or see how
many small craters (called craterlets) in a
given area you can observe. For example,
if you look at the f loor of Plato Crater,
a medium-size scope will reveal
four craterlets, each about
1¼ miles (2 kilometers) across.
By the way, any quality tele-
scope — of any type — will reveal
lots of lunar details. Whether you
own a 3-inch refractor, a 6-inch ref lec-
tor, or a 14-inch SCT, you’ll see a lot.
Observers without a permanent observa-
tory usually pick a scope they can set up
many nights in a row.
Because the Moon is so brilliant, espe-
cially through a telescope, observers
often use a neutral density filter to reduce
its light. Such an accessory is great
because it doesn’t change anything else
about the view.Michael E. Bakich is a contributing editor
of Astronomy.12
LEFT:^ NASA/GSFC/ASU