Sky & Telescope - April 2024 - 13

Backyard
know the structure of other galaxies - tens of millions
of light-years away - much better than we know the
structure of what lies within a few thousand light-years
of the Sun.
As a galactic cartographer, I aim to change that. The
goal of my research is to build more accurate maps of
the Milky Way's structure. I care about the nitty-gritty
details in artists' impressions because to know our
galaxy's structure is to know its history, and in particular,
the history of its youngest stars. In this article, I'll
present work my collaborators and I have done to map
stellar nurseries in the solar neighborhood. Our research
reveals a hitherto-unseen, colossal gaseous structure;
forces a revision to the shape of the closest spiral arm in
maps of our galaxy; and sheds new light on how the baby
stars in our corner of the Milky Way may have formed.
I care about the nitty-gritty
details in artists' impressions,
because to know our galaxy's
structure is to know its history.
The Distance Dilemma
To turn 2D images of the night sky into a 3D model
of the Milky Way, we first need to know how far
away things are. Yet distances have been a challenge
in astronomy for as long as the field has existed. My
favorite example of the need for accurate distances is
the Great Debate, which took place in 1920 between the
astronomers Harlow Shapley and Heber Curtis. They
were debating whether celestial objects known as " spiral
nebulae " were small and nearby or big and far away -
because confusion about distance leads to confusion
about size.
Curtis argued that the Sun sat near the center of a
small Milky Way and that spiral nebulae were external
galaxies. In contrast, Shapley argued that spiral nebulae
were nearby gas clouds, and that the universe contained
only one very large galaxy, with the Sun situated far
from its center.
Over the next decade, new observations largely
resolved the debate - and proved the two astronomers
both right and wrong. In the mid-1920s, Edwin
Hubble observed and analyzed Cepheid variable stars
in Andromeda, the closest spiral nebula. He deduced
that the nebula was much farther than even Shapley's
proposed extent of the Milky Way. Andromeda had to
be an external galaxy separate from our own, as Curtis
had argued. But history ultimately proved Shapley the
winner regarding both the Milky Way's large size and the
location of our Sun closer to its outskirts.
THE RADCLIFFE WAVE A new technique is showing the Milky
Way in 3D, revealing previously unseen structures like the Radcliffe
Wave, a sinusoidal alignment of stellar nurseries.
sk yand tele scope .o r g * APRIL 2024 13

http://skyandtelescope.org

Sky & Telescope - April 2024

Table of Contents for the Digital Edition of Sky & Telescope - April 2024

Contents
Sky & Telescope - April 2024 - Cover1
Sky & Telescope - April 2024 - Cover2
Sky & Telescope - April 2024 - 1
Sky & Telescope - April 2024 - Contents
Sky & Telescope - April 2024 - 3
Sky & Telescope - April 2024 - 4
Sky & Telescope - April 2024 - 5
Sky & Telescope - April 2024 - 6
Sky & Telescope - April 2024 - 7
Sky & Telescope - April 2024 - 8
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Sky & Telescope - April 2024 - Cover3
Sky & Telescope - April 2024 - Cover4
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