Sky & Telescope - September 2019 - 6

FROM OUR READERS

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I just ﬁnished reading "JunoCam at Jupiter: Where Science Meets Art" (S&T: May
2019, p. 14), and I'm rather surprised no one mentioned the resemblance between
some of the images and Vincent van Gogh's painting "The Starry Night." The image
on the lower half of page 17 in particular looks like an interpretation of the painting.
Is this coincidence, or were some of the image processors trying to imitate the effect?
Michael Farmer * Athens, Ohio
p Some of the images of Jupiter taken with JunoCam look surprisingly familiar.

Way Up North

6

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Tony Flanders replies: I was

Circular Reasoning

I found your comments about observing Omega Centauri from northern
latitudes (S&T: Apr. 2019, p. 22) very
interesting, particularly observations
from Point Pelee National Park. Our
local astronomy club (RASC - Windsor Centre) has been attempting this
observation for many years, with local
member Dan Taylor credited with being
the ﬁrst to do so in 1988. We've had
many successful attempts and have
learned that the ideal conditions occur
in March, when the air temperature
and water temperature on Lake Erie are
about the same and there is still ice on
the lake. Of course, this means observing at 3:00 a.m. before and 2:00 a.m.
after the start of Daylight Saving Time.
From our typical observing location
on the West Beach of Point Pelee, the
latitude is 41.93°N, and using a declination for Omega Cen of -47.5° you can
see that it gets only about a half degree
above the horizon. Of course, refraction
gives us another half degree, so we clear
the horizon by a full degree; however,
atmospheric extinction causes about a
9-magnitude drop in brightness.

aware of the initial observation,
but I had no idea that attempting to reobserve it had become an annual event.
That is very cool.
The northernmost sighting that
I'm aware of, from Cape Ann in
Massachusetts, is a few tenths of a
degree north of Point Pelee. It's no doubt
signiﬁcant that Cape Ann has many high
bluffs overlooking the ocean. Even so, only
the top two-thirds of the cluster was seen
and photographed.
I wonder if this was, in fact, the
northernmost sighting of Omega Cen, or if
there are other contenders.

In your recent article about gravitational lensing (S&T: May 2019, p. 28),
the diagram on page 30 raises some very
interesting questions. Once light from
a distant star, galaxy, or quasar is bent,
what happens to the light? Does it continue in its new direction indeﬁnitely?
If the light beam has really been curved,
will it eventually end up in a circle?
Maybe that idea is not so far-fetched.
If I'm not mistaken, wasn't it Einstein
that said if you could be on a rocket
traveling close to the speed of light,
you'll eventually end up in the same
place you started?

Solar System Shortcut?

Ralph Fusco
Edison, New Jersey

Steve Mastellotto
Tecumseh, Ontario

Joel Marks
Milford, Connecticut

S E P TE M B E R 2 019 * SK Y & TELESCOPE

The illustration accompanying the
News Note about Voyager 2 entering
interstellar space (S&T: Apr. 2019, p. 9)
has me wondering: Wouldn't it have
taken much, much longer for the Voyagers to enter interstellar space if they had
been traveling in a different direction?
The illustration appears to show them
emerging from the solar system proper
at the front of a bow shock. Was this
just a lucky break?

"

Camille Carlisle replies: Once

deﬂected, light would continue
on its new path as long as it doesn't
encounter anything else to change its
trajectory. But light is only deﬂected a little
bit by a gravitational lens, nowhere near
what would be needed to make it travel in
a circle. The only place I know of where
light is bent into a complete circular path
is just outside the horizon of a black hole.
There, light can be temporarily trapped
in a circular orbit, but it can eventually

JUPITER: N ASA / MSSS / G ER A LD EICHSTÄ DT / SE Á N DOR A N,
THE STA RRY NIG H T: M USEU M OF M ODER N A RT / PUBLIC DO M AIN

Post-Impressions of Jupiter

Monica Young replies: You're
right that the shape of the
heliosphere is decidedly asymmetrical,
and so the path taken by an interstellarbound spacecraft matters. Pioneer 10,
for example, is heading out of the solar
system, but because it's heading into the
"tail" of the heliosphere, it's going to be
a lot longer before it reaches interstellar
space. Voyagers 1 and 2 (and Pioneer 11)
were on different trajectories, but all were
going more or less toward the "head" of
the heliosphere. Whether astronomers
planned to send three of the four on a
short course out of the solar system, I'm
not sure. They would have known the
rough shape of the solar system before
the spacecraft launched, but they also
had a lot of other factors to consider. For
example, Voyager 1 was optimized for a
Titan ﬂyby and Voyager 2 was intended
for a "grand tour" of the solar system, and
their trajectories were planned accordingly.
Sky & Telescope - September 2019

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