16 ASTRONOMY • MARCH 2020
SECRET SKY
I n v isu a l a st ronomy, it ’s e a s y to m is s t he fore st
for the trees. Sometimes, we become so
focused on what we want to see that we can
easily miss out on what else there is to see — even if it
isn’t real.
The thin lunar crescent is a perfect example. How
many times have I looked at the old Moon in the new
Moon’s arms and missed (or ignored) an amazing,
well-known phenomenon usually associated with
transits of Venus? How appropriate that the young
Moon wears a mischievous Cheshire-cat grin early in
each of its lunations.Saber’s beads
First, the lunar blackdrop is different from what’s
become informally known as Saber’s beads, a phenom-
enon occurring when the Moon is less than one day from
its New phase. Then, it shows staggered brightness peaks
along the crescent, reminiscent of mini-Bailey’s beads.
Since Illinois amateur astronomer Stephen Saber
first described “his” beads in 2006, others have linked
his description to all manner of phenomena. The oldest
are Galileo’s 1609 telescopic observations: The cele-
brated astronomer noted in The Sidereal Messenger that
at “the ends of the upper and lower cusps also certain
bright points, quite away from the rest of the bright part,
began to rise out of the shadow.” Modern telescopicTake a closer look at the thin crescent Moon.
The lunar
blackdrop effect
- A 21-hour-young
Moon (with Cheshire-
cat grin) and Venus
share the low western
sky as seen from
Maun, Botswana, on
September 29, 2019.
IMAGES BY STEPHEN JAMES
O’MEARA, UNLESS NOTED
BY STEPHEN
JAMES O’MEARA
Stephen is a globe-
trotting observer who
is always looking
for the next great
celestial event.1
2