44 AUSTRALIAN SKY & TELESCOPE November | December 2017
UNDER THE STARS by Fred SchaafA trio of stellar prototypes
It’s no wonder that variable stars have
astronomers’ attention for years on eT
racking variable stars requires
meticulous observation habits,
with careful attention paid to
a single characteristic of a star — its
brightness. Many amateur astronomers
lean toward observing larger, richer,
more detailed or more colourful deep
sky objects, presuming that monitoring
variable stars requires more work or
more prolonged effort than they want
to put out.
So you may be surprised to learn
that three of the greatest amateur
astronomers of the 20th century, all
widely famed for their interest in more
visually rich classes of astronomical
objects, all widely treasured for their
skilled and beautiful astronomical
writing, were devoted, masterful and
passionate observers of variable stars.
These three great amateur astronomers
are, in chronological order: William
Tyler Olcott, Leslie Peltier and Walter
Scott Houston. It is interesting to
ponder the topic of variable stars
and what may have inspired the interest
of these men in them.
Three of the most important,
‘prototypical’ variable stars are: Delta
(b) Cephei, the prototype of the Cepheid
variable class; Omicron (k) Ceti (Mira),
the prototype of long-period or Mira
variables; and Beta (`) Persei (Algol), the
prototype of eclipsing binaries.
Delta Cephei is a pulsating star that
drops in brightness from magnitude
3.5 to 4.4 and back to maximum in
5 days, 8 hours and 48 minutes. It
forms a small triangle with excellent
comparison stars for its maximum and
minimum, and it’s also an easy orange
and blue double star.
Delta heads a class of variable star
known as the ‘Cepheids,’ which offered
us a key to establishing distances in
the universe. The variability of DeltaCephei was discovered in 1784 by
astronomer John Goodricke. Goodricke
lost his hearing after falling ill at age
5, but he received a solid education in
mathematics and natural philosopy
nonetheless. He died of pneumonia at
the age of 21, but not before proposing
the correct explanation for the
variability of Algol.
Mira is a long-period variable in the
neck of Cetus, the Whale, which goes
from one maximum to the next in about
332 days. Mira typically ranges from
about 9th or 10th magnitude to 4th or
3rd magnitude, but it occasionally peaks
at 2nd magnitude — and once even
rivaled 1st-magnitude Aldebaran.
Mira is approximately 500 times the
diameter of the Sun and so cool (for
a star) that it has water vapour in its
outer atmosphere. The star’s variability
was first noticed by German pastor
David Fabricius back on August 13,
1596, but he seems to have believed it
was a nova.
Algol marks the severed head of the
monster Medusa in the grasp of Perseus.Algol dims from magnitude 2.1 to 3.4
over a period of 2 days, 20 hours, 48
minutes and 56 seconds, with both the
dimming and brightening taking about
5 hours each. Though Goodricke was
the first to figure out Algol dims due to
eclipses by its cooler companion star, the
variability of Algol seems first to have
been recorded by Italian astronomer
Geminiano Montanari in 1667.
From the latitude of Sydney, Algol
rises to about 15 degrees above the
northern horizon after midnight in
mid-November; Mira is nice and high
in the northern sky; but Delta Cephei is
too far north for us to see.
I’ve only just gestured at the
accomplishments of Goodricke,
Fabricius, and Montanari this month,
but in a future column I’ll go into more
detail about Olcott, Peltier and Houston
mentioned above and their love of
variable stars.■ Contributing Editor FRED SCHAAF
was long ago struck by the wonder of
variable stars. ISTOCKPHOTOS.COM / ZU_09eheld
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