49
An artist’s impression shows
material flowing from Mira A (right)
onto the hot disk around its companion
white dwarf Mira B (left). The hot gas
in the system emits X-rays.See also: The geocentric model 20 ■ The Tychonic model 44–47 ■ Elliptical orbits 50–55 ■
Variable stars 86 ■ Measuring the universe 130–37
THE TELESCOPE REVOLUTION
To Fabricius’s amazement, a few
days later, the brightness of this
star had increased by a factor of
about three. After a few weeks, it
disappeared from view altogether,
only to reappear some years later.
In 1609, Fabricius confirmed that
Mira Ceti was a periodic variable
star, showing that, contrary to the
prevailing Greek philosophy that
the cosmos was unchanging, stars
were not constant.
Working with his son Johannes,
Fabricius also used a camera
obscura to look at the sun. They
studied sunspots, observing that
the spots moved across the sun’s
disk from east to west at a constant
speed. They then disappeared,
only to reappear on the other side,
having been out of sight for the
same time that it had taken them
to move across the sun’s disk. This
was the first concrete evidence thatthe sun rotated, providing further
proof of the variable nature of
heavenly bodies. However, the book
they published on the subject in
1611 was mostly overlooked, and the
credit for describing the movement
of sunspots went to Galileo, who
published his results in 1613.Double-star system
It is now known that Mira Ceti is a
double-star system 420 light-years
away. Mira A is an unstable red
giant star, about 6 billion years old
and in a late phase of its evolution.
It pulses in and out, changing not
only its size but also its temperature.
During the cooler part of its cycle,
it emits much of its energy as
infrared radiation rather than
light, so its brightness diminishes
dramatically. Mira B is a white
dwarf star surrounded by a disk of
hot gas that is flowing from Mira A. ■David Fabricius
David Fabricius was born in
1564 in Esens, Germany, and
studied at the University of
Helmsted. He later became
a Lutheran pastor for a group
of churches in Frisia.
Together with his son
Johannes (1587–1615), he was
fascinated by astronomy and
an avid user of early telescopes,
which his son had brought
back with him from a trip to
the Netherlands. Fabricius
corresponded extensively
with Johannes Kepler, withwhom Fabricius pioneered
the use of a camera obscura
to observe the sun.
Little is known of Fabricius’s
life beyond his letters and
publications. He died in 1617
after he was struck on the
head with a shovel by a local
goose thief, whom he had
denounced from the pulpit.Key work1611 Narration on Spots
Observed on the Sun and their
Apparent Rotation with the Sun
(with his son Johannes)In short, this new star
signifies peace ... as well as
change in the [Holy Roman]
Empire for the better.
David Fabricius
in a letter to
Johannes Kepler