June 3, 2021
Guest Speaker: Catherine Zucker, PhD
Dr. Catherine Zucker was introduced to the members and guests by George Bokinsky. She is a
2015 graduate of the University of Virginia with B.A. in both Astronomy-Physics and History and
William Holding Echols scholar during her time at UVa. She received her PhD in Astronomy and
Physics from Harvard University in 2017 and, at the time of her presentation, was a
Postdoctoral Fellow at the Center for Astrophysics with plans to continue her research in the
Hubble Fellowship Program at the Space Telescope Science Institute in Baltimore, Md. She is
the author or co-author of 28 publications including the subject of the presentation.
She discussed the findings of her research published “A Galactic-scale gas wave in the solar
neighborhood” published in Nature online 7 January 2020 as being part of her interest in the
gas-molecular structure of the Milky Way as the site of star formation. Studies of the Milky Way
from Earth’s location within its boundaries prevents a distant perspective leading to the need to
sample nearby gas structures using various resources such as Gaia space telescope and
selective wavelengths of light.
The images of the Milky Way are largely artist’s conceptions with UGC 12158 serving as the
Milky Way analog. The Spitzer Infrared Nearby Galaxy Survey (SINGS) Hubble Tuning Fork
galaxy classification scheme was used to show various classes of galaxies.
Turning from the general to the particular, Dr. Zucker illustrated the location of Sun within the
spiral arm of the Milky Way from both a “bird’s eye” view from above and edge-on. The area of
interest narrowed leading to the specific area of interest in the Solar Neighborhood as being the
Orion Nebula as viewed from Earth followed by an analysis of the electromagnetic spectrum of
this nebula used in the analysis.
Reasons for interest in this nebula relay to the five-step star and planet formation process:
Star forming cloud -> 2. Star forming core -> 3. Protostar -> 4. Circumstellar disk -> 5. Solar
system. Each step in the process was illustrated.
The results of the research lead to a change in the view of our solar neighborhood from the
before 2020 concept known at Gould’s belt to a more accurate conception known as the
Radcliffe Wave, a structure 9000 ly long, 400 ly wide with crest and trough reaching 500 ly out
of the galactic plane with gas mass > 3,000,000 time the mass of Sun.
Determining the location of the clouds involved precision astrometry measurements of parallax
to selected stars and locating the distance to the clouds by the reddening of light from the stars
by the intervening clouds. Knowing the star distance constrains the distances to the clouds.
Examples of this method were describe along with images taken in South America as part of
Dr. Zucker described goals for the next 4 years in further advancing this research as well as
other available resources including the Worldwide Telescope and plans to link telescopes
electronically showing objects of interest from different telescopes in different wavelengths of
light. Extended discussion with Dr. Zucker followed.
The meeting also included a presentation by Dr. Russ Pinizzotto on two constellations – Ursa
Minor and Leo Minor.