The Farthest Star
The author walks us through progressive steps outside of
our solar system in his quest for the farthest visible star.
H
ave you ever stood on a bit of land
where you could climb no higher,
or go no farther in the direction toward
a place you always dreamed of visit-
ing? During the week of the total solar
eclipse in 1991, my wife and I visited
Ka Lae, Hawai‘i, the southernmost
point of the island chain and also of the
United States. To linger there for a time
and wonder what lay beyond was like a
prescient moment. What I didn’t know
then was that two decades later I would
venture to Australia, the fi rst land a
Hawaiian sailor would fi nd if setting off
in the correct direction. Five thousand
miles away I would again watch the
Moon’s shadow block the Sun. Between
Ka Lae and Kona, where we saw totality,lies a small memorial to James Cook.
The British explorer mapped many of
the most distant points on Earth in the
18th century, was the fi rst European to
visit eastern Australia, and died on the
western shore of Hawai‘i.
In a cosmic correlation, I often won-
der when I view the sky how far I can
see in a given direction. Using only our
eyes, looking toward Sagittarius we run
into the dense gas and dust of our gal-
axy’s plane before we reach its center,
around 26,000 light-years away. Turn-
ing to Andromeda and its iconic galaxy,
we have 2.5 million light-years to M31,
and in Centaurus it’s about fi ve times
farther to the brightest radio galaxy,
ES Centaurus A (NGC 5128), possibly the
O
skyandtelescope.com • NOVEMBER 2019 57most distant object visible to the naked
eye. With binoculars or a telescope the
exercise becomes more complex.Choosing Our Targets
I recently wondered which is the far-
thest star that can be seen. It’s not a
trivial problem, as many factors, such as
experience, site conditions, and weather
affect the answer. Assuming a clear
view to the object, the two most impor-
tant factors are the limiting magnitude
of the instrument used and the charac-
teristics of the individual star. The latter
are easily looked up in standard star
charts and catalogs, and most observers
have a good feel for how faint a star will
be visible in their telescopes under good
conditions. The challenge is picking a
well-studied, intrinsically brilliant star
near that limit.Going Deep by Dave TostesonpPRIME HUNTING GROUNDS At a distance
of 6.3 million light-years in the constellation
Sculptor, NGC 300 is an ideal target in the
search for the farthest star visible from Earth.#56
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