Sky & Telescope - January 2022 - 12

COSMIC RELIEF by David Grinspoon
Many Happy Returns
Venus's eight-year cycle has the author dreaming of 2029.
AS I WRITE THIS IN SEPTEMBER,
Venus is wrapping up another magnificent
appearance as the Evening Star. All
summer and fall it has beamed through
the dusk as the sky has darkened before
following the Sun to exit, stage West.
It's a stirring and comforting sight, and
I always look forward to another visit
from this stunning old friend.
Venus repeatedly passes us on an
inside lane, swinging between dawn
and dusk in its never-ending 19-month
cycle. It approaches Earth in the evening,
pulls out in front of us in the
morning, then races around to come up
behind us again.
Our sister planet laps us almost
exactly five times every eight years. (A
Venusian would say the passing repeats
every 13 Venus years.) This 8:13 meanmotion
resonance is not perfect - it
slips by two days every eight years - and
its origin is not understood. But for
millennia humans have observed and
recorded this repeating cycle.
In any given year, Venus slowly traces
out a peculiar shape against the sky.
The exact pattern will depend on your
latitude. Where I live at a mid-northern
latitude (see diagram), Venus in its
most recent apparition first appeared
Venus 2021 Evening Apparition
30 minutes after sunset
Latitude 35° North
10°
Greatest brightness (-4.7)
Dec 1
Sep 1
Oct 29
Greatest elongation
(47°E)
SW
Oct 1
Jan 1, 2022
Aug 1
July 1
in late April 2021 about 20° north of
due West. It rose higher each night
for a few weeks before turning south
in early June. In October it will reach
greatest elongation, lingering for awhile
into the darkness at the extremity of
its orbit as seen from Earth. December
will see it reverse course, heading north
and plunging downwards into the solar
glare, to finally disappear in January.
The whole thing makes a sort of lopsided,
tilted infinity sign, with the larger
lobe disappearing over the horizon.
This month, Venus again becomes
the Morning Star, and it will stay that
way until its next evening apparition
starting in November. But the pattern
then will be markedly different from
what you see below, as a result of the
ecliptic's north-south seasonal tilt. The
following three evening appearances
will also be distinct, tracing new shapes
over time.
Then something wonderful happens.
The sixth appearance, beginning exactly
eight years after the first, will repeat
the first. And each successive return
will imitate the one five cycles earlier.
Thus, Venus outlines five distinct shapes
in the sky, each of which repeats every
eight years.
The Maya and Aztecs had different
names and glyphs for each of the five
appearances, which figured prominently
in their origin stories and calendar
cycles. Today, with our libraries full of
planetary data and detailed imagery
from spacecraft missions, we're distracted
from these splendid patterns.
When I see my brilliant
companion, I know that, eight
years hence, it will be right
back in the same spot again.
But bright Venus, undiminished even in
light-polluted skies, remains there for
any of us to observe.
Having trained myself to be aware of
these patterns, I often use Venus cycles
to mark eight-year anniversaries. When
I see my brilliant companion, I know
that, eight years hence, it will be right
back in the same spot again.
This year I'm aware of something
new and to me tremendously exciting.
My colleagues and I have worked for
more than 3 Venus cycles (since the late
1990s) to send new missions to Venus.
And now I'm finally on a team selected
to do so. We'll build and fly a spacecraft
called DAVINCI, which will be the first
entry probe NASA has sent there since
1978 (S&T: Sept. 2021, p. 10).
The launch is tentatively planned for
June
2021
summer 2029 - one Venus cycle from
now. This evening I'll look at the planet
and know that, with luck and perseverance,
the next time I see it at this same
spot in the sky, our little machine will
be on its way there.
WSW
12 JANUARY 2022 * SKY & TELESCOPE
W
WNW
¢ DAVID GRINSPOON is author of Venus
Revealed: A New Look Below the Clouds
of Our Mysterious Twin Planet.

Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022

Contents
Sky & Telescope - January 2022 - Cover1
Sky & Telescope - January 2022 - Cover2
Sky & Telescope - January 2022 - 1
Sky & Telescope - January 2022 - Contents
Sky & Telescope - January 2022 - 3
Sky & Telescope - January 2022 - 4
Sky & Telescope - January 2022 - 5
Sky & Telescope - January 2022 - 6
Sky & Telescope - January 2022 - 7
Sky & Telescope - January 2022 - 8
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Sky & Telescope - January 2022 - 11
Sky & Telescope - January 2022 - 12
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Sky & Telescope - January 2022 - Cover3
Sky & Telescope - January 2022 - Cover4
Sky & Telescope - January 2022 - SA1
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