Sky & Telescope - June 2021 - 6

FROM OUR READERS

Teaching Astronomy to the Visually Impaired

The Women Behind
RCB Stars
Greg Bryant's " The Ups and Downs
of RCB Stars " (S&T: Mar. 2021, p. 30)
missed out on an opportunity to tell a
multi-decade diversity story. The fact
that most stars have nearly the same
surface composition was the discovery
of Cecilia Helena Payne
(later Payne-Gaposchkin) in
1925. Valerie P. Myerscough
created the ﬁrst model
X Cecilia Helena Payne-Gaposchkin was a British-American astronomer who in 1925 discovered
that stars are composed primarily
of hydrogen and helium.

JUNE 2 021 * SK Y & TELESCOPE

Virginia Trimble
Irvine, California

Helium White Dwarfs
S NASA has released a series of digital models with files that enable 3D printers to create
models of the X-ray universe (see chandra.
harvard.edu/deadstar) like this one of the
remnant of Supernova 1006. They're excellent
tools for teaching tactile and visually impaired
learners about astronomy.

to create tactile representations of the
constellations using different sized
and shaped hardware nuts glued to the
inside of the tents to represent the different brightnesses of the stars and tape
for the constellation lines. Brilliant!
My mother would have been delighted
by this teacher's creativity and enthusiasm, to say nothing of how pleased she
would have been by Noreen Grice's book.
It's wonderful that there are resources
like this cleverly designed book.
John Craig * Orem, Utah

atmosphere of R Coronae Borealis and
demonstrated that helium and carbon
were the dominant elements [https://
is.gd/Myerscough1968]. Anne B.
Underhill violently opposed the model
and claimed (until her death) that the
star had a normal composition but
anomalous ionization and excitation.
A [1972] study of pulsating helium stars conﬁrmed that one could ﬁt the
period and amplitude of the
Cepheid-like pulsations of
RY Sagittarii with its effective temperature, around
6000K, a luminosity of
almost 20,000 times that of

I enjoyed reading " The Ups and Downs
of RCB Stars. " The author writes that the
progenitors of the helium white dwarfs
are very low-mass stars. I was wondering what the mass and expected lifetime
of helium white dwarf progenitor stars
are, and if the existence of a helium
white dwarf is compatible with the age
of the universe. I remember reading that
the lowest-mass stars burn their fuel
so slowly that they haven't had time to
reach the white dwarf state yet.
Paul Waddington
Rome, Italy

Greg Bryant replies: It's generally
believed that helium white dwarfs
don't form in a solitary environment. Rather,
they reach this evolutionary phase in a
binary system in which the companion star
strips the white dwarf of matter, bringing it
down to below around 0.5 solar masses, at
which point it can't fuse helium. The helium
white dwarfs that have been found thus far
are in the 0.2-0.5 solar-mass range. As with
other white dwarfs, helium white dwarfs are
thought to then slowly cool and fade until
they eventually become black dwarfs - the
timeframe for this is estimated to be longer
than the current age of the universe.

The Origin of Theia
Nola Taylor Redd's " How Did We Get the
Asteroid Belt? " was a joy to read (S&T:
Mar. 2021, p. 22). Yet I couldn't help but
think about the origin of the large planetoid that astronomers believe crashed
into Earth early in the solar system's
history, bounced off, and formed our
atypically large Moon. Could the lunar
progenitor have come from the early
planetoid chaos described in the article?

3D PRIN T: N ASA / CXC / SAO / K . A ND C. A RCA ND; PAY NE- G A POSCHK IN:
SMITHSONIA N INSTIT U TION A RCHIV ES / SCIENCE SERVICE RECORDS

Kate Crohan's review of Touch the Stars
(S&T: Feb. 2021, p. 68) reminded me
of my mother, Ruth Craig, who was
involved in teaching blind students
and training teachers of the blind.
She wrote the ﬁ rst tutorial textbook
for the Nemeth Code, which used to
represent mathematics in Braille. I
was also reminded of one of the most
engaging presentations on astronomy
I have ever seen. It was several years
ago at the Rocky Mountain Star Stare.
The presenter, Ben Wentworth, was a
former Air Force ofﬁcer who had taken
a job teaching the visually impaired.
He repeatedly said he wasn't a trained
teacher, but clearly he was a born one.
I will mention just a few of the
clever means he had used to present
astronomical concepts. One of the
best was standing a volunteer against
a Sun-warmed wall and having the
other kids squirt water at them. When
the volunteer stepped away, the dry,
warmer part of the wall behind them
became a " water shadow. " Shadows
are a tricky concept for blind students.
Combining that idea with a stake
driven into the ground and a buzzer
powered by a solar cell helped the students learn about the changing angle
of the Sun's rays. His pièces de résistance
were dome tents that his students used

the Sun, and a mass of about 2 Suns, if
and only if, the atmosphere contained
mostly helium plus some extra carbon.
The pulsation light curve was the work of
the late Michael Feast, but we have to let
the men have some of the fun. Oh, and
the 1972 author is also a woman, though
I'm a good deal older than I was then
[https://is.gd/Trimble_1972].

https://www.is.gd/Trimble_1972 http://www.chandra.harvard.edu/deadstar http://www.harvard.edu/deadstar https://www.is.gd/Myerscough1968 https://www.is.gd/Myerscough1968

Sky & Telescope - June 2021

Table of Contents for the Digital Edition of Sky & Telescope - June 2021